ABINIT, basic input variables:
List and description.
This document lists and provides the description
of the name (keywords) of the "basic" input
variables to be used in the main input file of the abinis code.
The new user is advised to read first the
new user's guide,
before reading the present file. It will be easier to discover the
present file with the help of the tutorial.
When the user is sufficiently familiarized with ABINIT, the reading of the
~ABINIT/Infos/tuning file might be useful. For responsefunction calculations using
abinis, the complementary file ~ABINIT/Infos/respfn_help is needed.
Copyright (C) 19982004 ABINIT group (DCA, XG, RC)
This file is distributed under the terms of the GNU General Public License, see
~ABINIT/Infos/copyright or
http://www.gnu.org/copyleft/gpl.txt .
For the initials of contributors, see ~ABINIT/Infos/contributors .
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List of input variables

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Help files :
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Abinis (main)

Abinis (respfn)

Mrgddb

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AIM (Bader)

Cut3D
Files that describe other input variables:
 Developper variables, VARDEV
 File handling variables, VARFIL
 Geometry builder + symmetry related variables, VARGEO
 Groundstate calculation variables, VARGS
 GW variables, VARGW
 Internal variables, VARINT
 Parallelisation variables, VARPAR
 ProjectorAugmented Wave variables, VARPAW
 Response Function variables, VARRF
 Structural optimization variables, VARRLX
Content of the file : alphabetical list of "basic" variables.
A.
acell
angdeg
B.
C.
D.
E.
ecut
F.
G.
H.
I.
iscf
ixc
J.
jdtset
K.
kpt
kptnrm
kptopt
L.
M.
N.
natom
nband
ndtset
ngkpt
nkpt
nshiftk
nsppol
nstep
nsym
ntypat
O.
occopt
P.
Q.
R.
rprim
S.
shiftk
symrel
T.
tnons
toldfe
toldff
tolvrs
tolwfr
typat
U.
udtset
V.
W.
wtk
X.
xangst
xcart
xred
Y.
Z.
znucl
acell
Mnemonics: scAle CELL
Characteristic: EVOLVING, LENGTH
Variable type: real array acell(3)
Gives the length scales by which
dimensionless primitive translations (in "rprim") are
to be multiplied. By default, given in bohr atomic units
(1 bohr=0.5291772083 Angstroms), although Angstrom can be specified,
if preferred, since acell has the
'LENGTH' characteristics.
See further description of acell related to the
rprim input variable.
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 Complete list of input variables
angdeg
Mnemonics: ANGles in DEGrees
Characteristic:
Variable type: real array angdeg(3)
No Default (use rprim as Default).
Gives the angles between directions of
primitive vectors of the unit cell (in degrees),
as an alternative to the input array rprim .
Will be used to set up rprim,
that, together with the array acell, will be used to define the
primitive vectors.
 angdeg(1) is the angle between the 2nd and 3rd vectors,
 angdeg(2) is the angle between the 1st and 3rd vectors,
 angdeg(3) is the angle between the 1st and 2nd vectors,
If the three angles are equal within 1.0d12 (except if they are exactly 90 degrees),
the three primitive
vectors are chosen so that the trigonal symmetry that exchange
them is along the z cartesian axis :
R1=( a , 0,c)
R2=(a/2, sqrt(3)/2*a,c)
R3=(a/2,sqrt(3)/2*a,c)
where a^{2}+c^{2}=1.0d0
If the angles are not all equal (or if they are all 90 degrees), one will have the following
generic form :
 R1=(1,0,0)
 R2=(a,b,0)
 R3=(c,d,e)
where each of the vectors is normalized,
and form the desired angles with the others.
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 Complete list of input variables
ecut
Mnemonics: Energy CUToff
Characteristic: ENERGY
Variable type: real parameter
Used for kinetic energy cutoff
which controls number
of planewaves at given k point by:
(1/2)[(2 Pi)*(k+Gmax)]^{2}=ecut for Gmax.
All planewaves inside this "basis sphere" centered
at k are included in the basis (except if dilatmx
is defined).
Can be specified in Ha (the default), Ry, eV or Kelvin, since
ecut has the
'ENERGY' characteristics.
(1 Ha=27.2113961 eV)
This is the single parameter which can have an enormous
effect on the quality of a calculation; basically the larger
ecut is, the better converged the calculation is. For fixed
geometry, the total energy MUST always decrease as ecut is
raised because of the variational nature of the problem.
Usually one runs at least several calculations at various ecut
to investigate the convergence needed for reliable results.
For kpoints whose coordinates are build from 0 or 1/2,
the implementation of timereversal symmetry that links
coefficients of the wavefunctions in reciprocal space
has been realized. See the input variable istwfk.
If activated (which corresponds to the Default mode),
this input variable istwfk will allow to
divide the number of plane wave (npw) treated explicitly
by a factor of two. Still, the final result should be identical with
the 'full' set of plane waves.
See the input variable ecutsm, for the
smoothing of the kinetic energy, needed to optimize unit cell parameters.
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 Complete list of input variables
iscf
Mnemonics: Integer for SelfConsistentField cycles
Characteristic:
Variable type: integer parameter
Default is 5.
Control the selfconsistency.
Positive, nonzero values =>
this is the usual choice for doing the usual ground state (GS)
calculations or for structural relaxation, where
the potential has to be determined selfconsistently.
The choice between different algorithms for SCF is possible :
 =1 => get the largest eigenvalue of the SCF cycle
(DEVELOP option, used with
irdwfk=1 or
irdwfq=1)
 =2 => SCF cycle, simple mixing
 =3 => SCF cycle, anderson mixing
 =5 => SCF cycle, CG based on the minim. of the energy
 Other positive, including zero values, are not allowed.
The default option is iscf=5, which is a compromise between speed and reliability.
The value iscf=3 is safer but sometimes slower.
Other (negative) options:
 = 2 =>
a nonselfconsistent calculation is to be done;
in this case an electron density rho(r) on a real space grid
(produced in a previous calculation) will be read from a
disk file (automatically if ndtset=0, or
according to the value of getden
if ndtset/=0).
The name of the density file must be given as indicated
in the section 4 of abinis_help.
iscf=2 would be used for
band structure calculations, to permit computation of
the eigenvalues of occupied and unoccupied states at
arbitrary k points in the fixed self consistent potential
produced by some integration grid of k points.
To compute the eigenvalues
(and wavefunctions) of unoccupied states in a separate
(nonselfconsistent) run, the user should
save the selfconsistent rho(r)
and then run iscf=2 for the intended set of kpoints and bands.
To prepare a run with iscf=2, a density file
can be produced using the
parameter prtden (see its description).
When a selfconsistent set of wavefunctions is already available,
abinit can be used with
nstep=0 (see Test_v2/t47.in),
and the adequate value of prtden.
 = 3 =>
like 2, but initialize occ and wtk,
directly or indirectly (using ngkpt or
kptrlatt)
depending on the value of occopt.
For GS, this option
might be used to generate Densityofstates
(thanks to prtdos),
or to produce STM charge density map (thanks to prtstm).
For RF, this option is needed to compute the response to ddk perturbation.
 = 1 => like 2, but the nonselfconsistent calculation
is followed by the determination of excited states
within TDDFT. This is only possible for nkpt=1,
kpt=0 0 0,
nsppol=1. Note that the
oscillator strength needs to be defined with respect to
an origin of coordinate, thanks to the input variable
boxcenter. The maximal
number of KohnSham excitations to be used to build the
excited state TDDFT matrix can be defined by td_mexcit,
or indirectly by the maximum KohnSham excitation energy
td_maxene.
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 Complete list of input variables
ixc
Mnemonics: Integer for eXchangeCorrelation choice
Characteristic:
Variable type: integer parameter
Default is ixc=1 (Teter parameterization). However, if all the
pseudopotentials have the same value of pspxc, the initial value of ixc will be
that common value.
Control the choice of exchange and correlation (xc).
 1=> LDA or LSD, Teter Pade parametrization (4/93, published in S. Goedecker, M. Teter, J. Huetter, Phys.Rev.B54, 1703 (1996)), which
reproduces PerdewWang (which reproduces CeperleyAlder!).
 2=> LDA, PerdewZungerCeperleyAlder (no spinpolarization)
 3=> LDA, old Teter rational polynomial parametrization (4/91)
fit to CeperleyAlder data (no spinpolarization)
 4=> LDA, Wigner functional (no spinpolarization)
 5=> LDA, HedinLundqvist functional (no spinpolarization)
 6=> LDA, "Xalpha" functional (no spinpolarization)
 7=> LDA or LSD, PerdewWang 92 functional
 8=> LDA or LSD, xonly part of the PerdewWang 92 functional
 9=> LDA or LSD, x and RPA correlation part of the PerdewWang 92 functional
 11=> GGA, PerdewBurkeErnzerhof GGA functional
 12=> GGA, xonly part of PerdewBurkeErnzerhof GGA functional
 13=> GGA potential of van LeeuwenBaerends, while for energy, PerdewWang 92 functional
 14=> GGA, revPBE of Y. Zhang and W. Yang, Phys. Rev. Lett. 80, 890 (1998)
 15=> GGA, RPBE of B. Hammer, L.B. Hansen and J.K. Norskov, Phys. Rev. B 59, 7413 (1999)
 16=> GGA, HTCH of F.A. Hamprecht, A.J. Cohen, D.J. Tozer, N.C. Handy, J. Chem. Phys. 109, 6264 (1998)
 20=> FermiAmaldi xc ( 1/N Hartree energy, where N is the
number of electrons per cell ; G=0 is not taken
into account however), for TDDFT tests.
No spinpol. Does not work for RF.
 21=> same as 20, except that the xckernel is the LDA (ixc=1) one,
for TDDFT tests.
 22=> same as 20, except that the xckernel is the BurkePetersilkaGross
hybrid, for TDDFT tests.
Note that the choice made here should agree with the choice
made in generating the original pseudopotential, except
for ixc=0 (usually only used for debugging).
A warning is issued if this is not the case.
However, the choices ixc=1, 2, 3 and 7 are fits to the same data, from
CeperleyAlder, and are rather similar, at least for spinunpolarized systems.
The choice between the LDA or the LSD is governed
by the value of nsppol (see below).
NOTE : in the implementation of the spindependence of these
functionals, and in order to avoid divergences in their
derivatives, the interpolating function between spinunpolarized
and fullyspinpolarized function has been slightly modified,
by including a zeta rescaled by 1.d01.d6. This should affect
total energy at the level of 1.d6Ha, and should
have an even smaller effect on differences of energies, or derivatives.
The value ixc=10 is used internally : gives the difference between ixc=7 and
ixc=9, for use with an accurate RPA correlation energy.
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 Complete list of input variables
jdtset
Mnemonics: index J for DaTaSETs
Characteristic: NO MULTI
Variable type: integer array jdtset(ndtset)
Default : the series 1, 2, 3 ... ndtset .
Gives the dataset index
of each of the datasets. This index will be used :
 to determine which input variables are specific to each
dataset, since the variable names for this
dataset will be made from the bare variable
name concatenated with this index, and only if
such a composite variable name does not exist,
the code will consider the bare variable name,
or even, the Default;
 to characterize output variable names, if their
content differs from dataset to dataset;
 to characterize output files ( root names appended with _DSx
where 'x' is the dataset index ).
The allowed index values are between 1 and 99.
An input variable name appended with 0 is not allowed.
When ndtset==0, this array is not used, and moreover,
no input variable name appended with a digit is allowed.
This array might be initialized thanks to the use of
the input variable udtset. In this case, jdtset cannot
be used.
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 Complete list of input variables
kpt
Mnemonics: K  PoinTs
Characteristic:
Variable type: real array kpt(3,nkpt)
Default is 0. 0. 0. (for just one kpoint)
Contains the k points in terms
of reciprocal space primitive translations (NOT in
cartesian coordinates!).
Needed ONLY
if kptopt=0, otherwise
deduced from other input variables.
It contains dimensionless numbers in terms of which
the cartesian coordinates would be:
k_cartesian = k1*G1+k2*G2+k3*G3
where (k1,k2,k3) represent the dimensionless "reduced
coordinates" and G1, G2, G3 are the cartesian coordinates
of the primitive translation vectors. G1,G2,G3 are related
to the choice of direct space primitive translation vectors
made in rprim.
Note that an overall norm for the k
points is supplied by kptnrm. This allows
one to avoid supplying many digits for the k points to
represent such points as (1,1,1)/3.
Note: one of the algorithms used to set up the sphere
of G vectors for the basis needs components of kpoints
in the range [1,1], so the
remapping is easily done by adding or subtracting 1 from
each component until it is in the range [1,1]. That is,
given the k point normalization kptnrm described below,
each component must lie in [kptnrm,kptnrm].
Not read if kptopt/=0 .
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 Complete list of input variables
kptnrm
Mnemonics: K  PoinTs NoRMalization
Characteristic:
Variable type: real parameter
Default is 1.
Establishes a normalizing denominator
for each k point.
Needed only
if kptopt<=0, otherwise
deduced from other input variables.
The k point coordinates as fractions
of reciprocal lattice translations are therefore
kpt(mu,ikpt)/kptnrm. kptnrm defaults to 1 and can
be ignored by the user. It is introduced to avoid
the need for many digits in representing numbers such as 1/3.
It cannot be smaller than 1.0d0
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 Complete list of input variables
kptopt
Mnemonics: KPoinTs OPTion
Characteristic:
Variable type: integer parameter
Default is 0 .
Control the set up of the kpoints list.
The aim will be to initialize, by straight reading
or by a preprocessing approach based on other input variables,
the following input variables, giving the k points, their number,
and their weight:
kpt,
kptnrm,
nkpt,
and, for iscf/=2,
wtk.
Often, the k points will form a lattice in reciprocal space. In this case,
one will also aim at initializing input variables that give
the reciprocal of this kpoint lattice, as well as its shift with respect
to the origin:
ngkpt or
kptrlatt,
as well as on nshiftk and
shiftk.
 0=> read directly nkpt, kpt,
kptnrm and wtk
(corresponds to the usage before version 2.1)
One can use the kptgen utility to produce these input data.
 1=> rely on ngkpt or
kptrlatt, as well as on
nshiftk and
shiftk to set up the k points.
Take fully into account the symmetry to generate the
k points in the Irreducible Brillouin Zone only.
(This is the usual mode for GS calculations)
 2=> rely on
ngkpt or
kptrlatt, as well as on
nshiftk and
shiftk to set up the k points.
Take into account only the timereversal symmetry :
k points will be generated in half the Brillouin zone.
(This is to be used when preparing or executing a
RF calculation at q=(0 0 0) )
 3=> rely on ngkpt or
kptrlatt, as well as on
nshiftk and
shiftk to set up the k points.
Do not take into account any symmetry :
k points will be generated in the full Brillouin zone.
(This is to be used when preparing or executing a
RF calculation at nonzero q )
 (4=> has been replaced by negative values in version 2.3 )
 A negative value =>
rely on kptbounds,
and ndivk
to set up a band structure calculation along different lines
(allowed only for iscf==2).
The absolute value of kptopt gives the number of segments
of the band structure.
In the case of a grid of k points, the auxiliary variables
kptrlen,
ngkpt and
prtkpt might help
you to select the optimal grid.
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 Complete list of input variables
natom
Mnemonics: Number of ATOMs
Characteristic:
Variable type: integer parameter
Default is 1
Gives the total number of atoms in the unit cell.
Default is 1 but you will obviously want to input this
value explicitly.
Note that natom refers to all atoms in the unit cell, not
only to the irreducible set of atoms in the unit cell (using symmetry operations,
this set allows to recover all atoms). If you want
to specify only the irreducible set of atoms, use the
symmetriser, see the input variable natrd.
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 Complete list of input variables
nband
Mnemonics: Number of BANDs
Characteristic:
Variable type: integer parameter
Default is 1.
Gives number of bands, occupied plus
possibly unoccupied, for which wavefunctions are being computed
along with eigenvalues.
Note : if the parameter
occopt (see below) is not set to 2,
nband is a scalar integer, but
if the parameter occopt is set to 2,
then nband must be an array nband(nkpt*
nsppol) giving the
number of bands explicitly for each k point. This
option is provided in order to allow the number of
bands treated to vary from k point to k point.
For the values of occopt not equal to 0 or 2, nband
can be omitted. The number of bands will be set up
thanks to the use of the variable fband. The present Default
will not be used.
If nspinor is 2, nband must be even for
each k point.
In the case of a GW calculation (optdriver=3 or 4),
nband gives the number of bands to be treated to generate the screening (susceptibility
and dielectric matrix), as well as the selfenergy. However, to generate the _KSS
file (see kssform)
the relevant number of bands is given by nbandkss.
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 Complete list of input variables
ndtset
Mnemonics: Number of DaTaSETs
Characteristic: NO MULTI
Variable type: integer parameter
Default is 0 (no multidata set).
Gives the number of data sets to be
treated.
If 0, means that the multidata set treatment is not used,
so that the root filenames will not be appended with _DSx,
where 'x' is the dataset index defined
by the input variable jdtset,
and also that input names with a dataset index are not allowed.
Otherwise, ndtset=0 is equivalent to ndtset=1.
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 Complete list of input variables
ngkpt
Mnemonics: Number of Grid points
for K PoinTs generation
Characteristic: NOT INTERNAL
Variable type: integer array ngkpt(3)
No Default
Used when kptopt>=0,
if kptrlatt
has not been defined (kptrlatt
and ngkpt are exclusive of each other).
Its three positive components
give the number of k points of MonkhorstPack grids
(defined with respect to primitive axis in reciprocal space)
in each of the three dimensions.
ngkpt will be used to generate the
corresponding kptrlatt
input variable.
The use of nshiftk
and shiftk, allows to generate
shifted grids, or MonkhorstPack grids defined
with respect to conventional unit cells.
When nshiftk=1,
kptrlatt is initialized
as a diagonal (3x3) matrix, whose diagonal elements
are the three values ngkpt(1:3). When
nshiftk is greater than 1,
ABINIT will try to generate kptrlatt
on the basis of the primitive vectors of the klattice:
the number of shifts might be reduced, in which case
kptrlatt will not be diagonal
anymore.
MonkhorstPack grids are usually the most efficient when
their defining integer numbers are even.
For a measure of the efficiency, see the input variable
kptrlen.
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 Complete list of input variables
nkpt
Mnemonics: Number of K  Points
Characteristic:
Variable type: integer parameter
Default is 0 if
kptopt/=0, and 1 if
kptopt==0.
If nonzero,
nkpt
gives the number of k points in the k point array
kpt. These points
are used either to sample the Brillouin zone, or to
build a band structure along specified lines.
If nkpt is zero, the code deduces from other input variables
(see the list in the description of kptopt)
the number of k points, which is possible only
when kptopt/=0.
If kptopt/=0 and
the input value of nkpt/=0,
then ABINIT will check that the number of k points
generated from the other input variables
is exactly the same than nkpt.
If kptopt is positive,
nkpt must be coherent with the values
of kptrlatt,
nshiftk
and shiftk.
For ground state calculations, one should select the
k point in the irreducible Brillouin Zone (obtained
by taking into account point symmetries and the timereversal
symmetry).
For response function calculations, one should
select k points in the full Brillouin zone, if the wavevector
of the perturbation does not vanish, or in a half of
the Brillouin Zone if q=0. The code will automatically decrease
the number of k points to the minimal set needed for
each particular perturbation.
If kptopt is negative,
nkpt will be the sum of the number of points on
the different lines of the band structure.
For example,
if kptopt=3, one
will have three segments; supposing
ndivk is 10 12 17,
the total number of k points of the circuit will be
10+12+17+1(for the final point)=40.
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 Complete list of input variables
nshiftk
Mnemonics: Number of SHIFTs for K point grids
Characteristic:
Variable type: integer parameter
The Default is 1.
This parameter
gives the number of shifted grids
to be used concurrently to generate the full grid of k points.
It can be used with primitive grids defined either from
ngkpt
or
kptrlatt.
The maximum allowed value of nshiftk is 8.
The values of the shifts are given by shiftk.
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 Complete list of input variables
nsppol
Mnemonics: Number of SPin POLarization
Characteristic:
Variable type: integer parameter
The Default is 1.
Give the number of independent
spin polarisations. Can take the values
1 or 2.
If nsppol=1, one has an unpolarized calculation
(nspinor=1,
nspden=1) or
an antiferromagnetic system
(nspinor=1,
nspden=2), or
a calculation in which spin up and spin down cannot be disantengled
(nspinor=2),
noncollinear magnetism or presence of spinorbit coupling,
for which one needs spinor wavefunctions.
If nsppol=2, one has a spinpolarized calculation
with separate and different wavefunctions for up and
down spin electrons for each band and k point.
Compatible only with nspinor=1,
nspden=2.
In the present status of development,
with nsppol=1,
all values of ixc are allowed, while
with nsppol=2,
only ixc=0, 1, 7 and 11 are allowed.
See also the input variable nspden
for the components of the density matrix with respect to
the spinpolarization.
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 Complete list of input variables
nstep
Mnemonics: Number of selfconsistent field STEPS
Characteristic:
Variable type: integer parameter
Default is 1.
Gives the maximum number of SCF cycles (or "iterations").
Full convergence from random numbers if usually achieved in
1220 SCF iterations. Each can take from minutes to hours.
In certain difficult cases, usually related to a small or
zero bandgap, convergence performance may be much worse.
When the convergence tolerance tolwfr on the wavefunctions
is satisfied, iterations will stop, so for well converged
calculations you should set nstep to a value larger than
you think will be needed for full convergence, e.g.
if 20 steps usually converges the system, set nstep to 30.
NOTE that a choice of nstep=0 is permitted; this will
either read wavefunctions from disk (with irdwfk=1
or irdwfq=1,
or nonzero getwfk
or getwfq in the case
of multidataset) and
compute the density, the total energy and stop, or else
(with all of the above vanishing) will initialize
randomly the wavefunctions and
compute the resulting density and total energy.
This is provided for testing purposes.
One can output the density by using prtden.
Unlike the forces, the stress tensor also gets
computed with nstep=0.
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 Complete list of input variables
nsym
Mnemonics: Number of SYMmetry operations
Characteristic: SYMMETRY FINDER
Variable type: integer parameter
Default is 0.
Gives number of space group symmetries
to be applied in this problem. Symmetries will be input in
array "symrel" and (nonsymmorphic) translations vectors
will be input
in array "tnons". If there is no symmetry in the problem
then set nsym to 1, because the identity is still a symmetry.
In case of a RF calculation, the code is able to use
the symmetries of the system to decrease the number of
perturbations to be calculated, and to decrease of the
number of special k points to be used for the sampling of
the Brillouin zone.
After the response to the perturbations have been calculated,
the symmetries are used to generate as many as
possible elements of the 2DTE from those already
computed.
SYMMETRY FINDER mode (Default mode).
If nsym is 0, all the atomic coordinates must be
explicitely given (one cannot use the geometry builder
and the symmetrizer): the code will then find automatically
the symmetry operations that leave the lattice and each
atomic sublattice invariant. It also checks whether the
cell is primitive (see chkprim).
Note that the tolerance on symmetric atomic positions and
lattice is rather stringent :
for a symmetry operation to be admitted,
the lattice and atomic positions must map on themselves
within 1.0e8 .
The user is allowed to set up systems with nonprimitive unit cells (i.e.
conventional FCC or BCC cells, or supercells without any distortion).
In this case, pure translations will be identified as symmetries
of the system by the symmetry finder.
Then, the combined "pure translation + usual rotation and inversion" symmetry
operations can be very numerous. For example, a conventional FCC cell
has 192 symmetry operations, instead of the 48 ones of the primitive cell.
A maximum limit of 384 symmetry operations is hardcoded. This
corresponds to the maximum number of symmetry operations of a 2x2x2
undistorted supercell. Going beyond
that number will make the code stop very rapidly. If you want
nevertheless, for testing purposes, to treat a larger number of symmetries,
change the initialization of "msym" in the abinit.f main routine,
then recompile the code.
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 Complete list of input variables
ntypat
Mnemonics: Number of TYPEs of atoms
Characteristic: NO MULTI
Variable type: integer parameter
Default is 1.
Gives the number of types of atoms. E.g. for
a homopolar system (e.g. pure Si) ntypat is 1, while for BaTiO3,
ntypat is 3.
Except when alchemical mixing of pseudopotentials is used, the number
of types of atoms will be equal to the number of pseudopotentials
npsp to be provided by the user.
Thus, The code will try to read the same number of pseudopotential files,
whose names should have been given in the "files" file.
The first pseudopotential will be assigned the type number 1, and so
on ...
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 Complete list of input variables
occopt
Mnemonics: OCCupation OPTion
Characteristic:
Variable type: integer option parameter
The Default is occopt=1.
Control how input
parameters nband, occ,
and wtk are handled.
 occopt=0:
All k points have the same number of bands
and the same occupancies of bands. nband is given as a
single number, and occ(nband)
is an array of nband
elements, read in by the code.
The k point weights in array wtk(nkpt) are
automatically normalized by the code to add to 1.
 occopt=1:
Same as occopt=0, except that the array occ is
automatically generated by the code, to give a semiconductor.
An error occurs when filling cannot be done with
occupation numbers equal to 2 or 0 in each kpoint (nonspinpolarized case),
or with occupation numbers equal to 1 or 0 in each kpoint (spinpolarized case).
 occopt=2:
k points may optionally have different numbers of
bands and different occupancies. nband(
nkpt*nsppol) is given
explicitly as an array of nkpt*nsppol elements.
occ() is given explicitly for all bands at each k point,
and eventually for each spin 
the total number of elements is the sum of nband(ikpt)
over all k points and spins. The k point weights wtk
(nkpt) are
NOT automatically normalized under this option.
 occopt=3, 4, 5, 6 and 7
Metallic occupation of levels, using different occupation
schemes (see below). The corresponding thermal
broadening, or cold smearing, is defined by
the input variable tsmear (see below : the variable
xx is the energy in Ha, divided by tsmear)
Like for occopt=1, the variable occ is not read
All k points have the same number of bands,
nband is given as a single number, read by the code.
The k point weights in array wtk(nkpt) are
automatically normalized by the code to add to 1.
 occopt=3:
FermiDirac smearing (finitetemperature metal)
Smeared delta function : 0.25d0/(cosh(xx/2.0d0)**2)
 occopt=4:
"Cold smearing" of N. Marzari (see his thesis work),
with a=.5634 (minimization of the bump)
Smeared delta function :
exp(xx^{2})/sqrt(pi) * (1.5d0+xx*(a*1.5d0+xx*(1.0d0+a*xx)))
 occopt=5:
"Cold smearing" of N. Marzari (see his thesis work),
with a=.8165 (monotonic function in the tail)
Same smeared delta function as occopt=4, with different a.
 occopt=6:
Smearing of Methfessel and Paxton (PRB40,3616(1989))
with Hermite polynomial of degree 2, corresponding
to "Cold smearing" of N. Marzari with a=0
(so, same smeared delta function as occopt=4, with different a).
 occopt=7:
Gaussian smearing, corresponding to the 0 order
Hermite polynomial of Methfessel and Paxton.
Smeared delta function : 1.0d0*exp(xx**2)/sqrt(pi)
WARNING : one can use metallic occupation of levels in the
case of a molecule, in order to avoid any problem with
degenerate levels. However, it is adviced NOT to use
occopt=6 (and to a lesser extent occopt=4 and 5),
since the associated number of electron
versus the Fermi energy is NOT garanteed to be
a monotonic function. For true metals, AND a sufficiently
dense sampling of the Brillouin zone, this should not happen,
but be cautious ! As an indication of this problem,
a small variation of input parameters might lead to
a jump of total energy, because there might be two or even
three possible values of the Fermi energy, and the
bissection algorithm find one or the other.
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 Complete list of input variables
rprim
Mnemonics: Real space PRIMitive translations
Characteristic: EVOLVING (if ionmov==2 and
optcell/=0)
Variable type: real array rprim(3,3)
Default : 3x3 unity matrix.
Give, in columnwise entry,
the three dimensionless primitive translations in real space.
If the Default is used, that is, rprim is the the unity matrix,
the three dimensionless primitive vectors are three
unit vectors in cartesian coordinates. Each will be multiplied
by the corresponding acell value to give the dimensional
primitive vectors, called rprimd.
In the general case, the dimensional cartesian
coordinates of the crystal primitive translations R1p, R2p and R3p, see
rprimd, are
 R1p(i)=rprim(i,1)*acell(1) for i=1,2,3 (x,y,and z)
 R2p(i)=rprim(i,2)*acell(2) for i=1,2,3
 R3p(i)=rprim(i,3)*acell(3) for i=1,2,3.
The rprim variable is thus used to define directions
of the primitive vectors, that will be multiplied by
the appropriate length scale acell(1), acell(2),
or acell(3)
respectively to give the dimensional primitive translations
in real space in cartesian coordinates.
Presently, it is requested that the mixed product
(R1xR2).R3 is positive. If this is not the case,
simply exchange a pair of vectors.
To be more specific, rprim 1 2 3 4 5 6 7 8 9 corresponds to input
of the three primitive translations R1=(1,2,3),
R2=(4,5,6), and R3=(7,8,9).
Note carefully that the first
three numbers input are the first column of rprim, the next
three are the second, and the final three are the third.
This corresponds with the usual Fortran order for arrays.
The matrix whose columns are the reciprocal space primitive
translations is the inverse transpose of the matrix whose
columns are the direct space primitive translations.
Alternatively to rprim, directions of dimensionless primitive
vectors can be specified by using the input variable angdeg.
This is especially useful for hexagonal lattices (with 120 or 60 degrees angles).
Indeed, in order for symmetries to be recognized, rprim must be symmetric up to 10 digits,
inducing a specification such as
rprim 0.86602540378 0.5 0.0
0.86602540378 0.5 0.0
0.0 0.0 1.0
that can be avoided thanks to angdeg:
angdeg 90 90 120
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 Complete list of input variables
rprimd
Mnemonics: Real space PRIMitive translations, Dimensional
Characteristic: INTERNAL, EVOLVING
(if ionmov==2 and
optcell/=0)
Variable type: real array rprimd(3,3)
This internal variable gives the dimensional real space primitive
vectors, computed from acell
and rprim.
 R1p(i)=rprimd(i,1)=rprim(i,1)*acell(1) for i=1,2,3 (x,y,and z)
 R2p(i)=rprimd(i,2)=rprim(i,2)*acell(2) for i=1,2,3
 R3p(i)=rprimd(i,3)=rprim(i,3)*acell(3) for i=1,2,3
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 Complete list of input variables
shiftk
Mnemonics: SHIFT for K points
Characteristic:
Variable type:
real array shift(3,nshiftk)
Default 0.5 0.5 0.5 ... 0.5
It is used only when kptopt>=0,
and must be defined if nshiftk is larger than 1.
shiftk(1:3,1:nshiftk) defines
nshiftk shifts
of the homogeneous grid of k points
based on ngkpt or
kptrlatt.
The shifts induced by shiftk corresponds
to the reduced coordinates in the coordinate system
defining the kpoint lattice. For example,
if the k point lattice is defined using ngkpt,
the point whose reciprocal space reduced coordinates are
( shiftk(1,ii)/ngkpt(1)
shiftk(2,ii)/ngkpt(2)
shiftk(3,ii)/ngkpt(3) )
belongs to the shifted grid number ii.
The user might rely on ABINIT to suggest suitable and
efficients combinations of kptrlatt
and shiftk.
The procedure to be followed is described with the
input variables kptrlen.
In what follows, we suggest some interesting values of the shifts,
to be used with even values of ngkpt.
This list is much less exhaustive than the abovementioned automatic
procedure.
1) When the primitive vectors of the lattice do NOT form
a FCC or a BCC lattice, the usual (shifted) MonkhorstPack
grids are formed by using
nshiftk=1 and shiftk 0.5 0.5 0.5 .
This is often the preferred k point sampling.
For a nonshifted MonkhorstPack grid, use
nshiftk=1 and shiftk 0.0 0.0 0.0 ,
but there is little reason to do that.
The FCC k point sampling defined with
nshiftk=4 and shiftk
0.5 0.5 0.5
0.5 0.0 0.0
0.0 0.5 0.0
0.0 0.0 0.5
is particularly efficient.
2) When the primitive vectors of the lattice form a FCC lattice,
with rprim
0.0 0.5 0.5
0.5 0.0 0.5
0.5 0.5 0.0
the usual MonkhorstPack sampling will be generated by using
nshiftk= 4 and shiftk
0.5 0.5 0.5
0.5 0.0 0.0
0.0 0.5 0.0
0.0 0.0 0.5
3) When the primitive vectors of the lattice form a BCC lattice,
with rprim
0.5 0.5 0.5
0.5 0.5 0.5
0.5 0.5 0.5
the usual MonkhorstPack sampling will be generated by using
nshiftk= 2 and shiftk
0.25 0.25 0.25
0.25 0.25 0.25
However, the simple sampling
nshiftk=1 and shiftk 0.5 0.5 0.5
is excellent.
4) For hexagonal lattices, one can use
nshiftk= 1 and shiftk 0.0 0.0 0.5
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 Complete list of input variables
symrel
Mnemonics:SYMmetry in REaL space
Characteristic:
Variable type: integer array symrel(3,3,nsym)
Default is the identity matrix for one symmetry.
Gives "nsym" 3x3 matrices
expressing space group symmetries in terms of their action
on the direct (or real) space primitive translations.
It turns out that these can always be expressed as integers.
Always give the identity matrix even if no other symmetries
hold, e.g.
symrel 1 0 0 0 1 0 0 0 1
Also note that for this array as for all others the array
elements are filled in a columnwise order as is usual for
Fortran.
The relation between the above symmetry matrices symrel,
expressed in the basis of primitive translations, and
the same symmetry matrices expressed in cartesian coordinates,
is as follows. Denote the matrix whose columns are the
primitive translations as R, and denote the cartesian
symmetry matrix as S. Then
symrel = R(inverse) * S * R
where matrix multiplication is implied.
When the symmetry finder is used (see nsym), symrel
will be computed automatically.
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 Complete list of input variables
tnons
Mnemonics: Translation NONSymmorphic vectors
Characteristic:
Variable type:
real array tnons(3,nsym)
Gives the (nonsymmorphic) translation
vectors associated with the symmetries expressed
in "symrel".
These may all be 0, or may be fractional (nonprimitive)
translations expressed relative to the real space
primitive translations (so, using the "reduced" system
of coordinates, see "xred").
If all elements of the space
group leave 0 0 0 invariant, then these are all 0.
When the symmetry finder is used (see nsym), tnons
is computed automatically.
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 Complete list of input variables
toldfe
Mnemonics: TOLerance on the DiFference of total Energy
Characteristic:
Variable type: real parameter
Default is 0.0 (stopping condition ignored)
Sets a tolerance for absolute differences
of total energy that, reached TWICE successively,
will cause one SCF cycle to stop (and ions to be moved).
Can be specified in Ha (the default), Ry, eV or Kelvin, since
ecut has the
'ENERGY' characteristics.
(1 Ha=27.2113961 eV)
If set to zero, this stopping condition is ignored.
Effective only when SCF cycles are done (iscf>0).
In this case, since toldfe, toldff,
tolvrs and tolwfr
are aimed at the same goal (causing the SCF cycle to stop),
one and only one of these must be specified.
Because of machine precision, it is not worth to try
to obtain differences in energy that are smaller
than about 1.0d12 of the total energy.
To get accurate stresses may be quite demanding.
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 Complete list of input variables
toldff
Mnemonics: TOLerance on the DiFference of Forces
Characteristic:
Variable type: real parameter
Default is 0.0 (stopping condition ignored)
Sets a tolerance for differences of forces
(in hartree/bohr) that, reached TWICE successively,
will cause one SCF cycle to stop (and ions to be moved).
If set to zero, this stopping condition is ignored.
Effective only when SCF cycles are done (iscf>0).
In this case, since toldfe, toldff,
tolvrs and tolwfr
are aimed at the same goal (causing the SCF cycle to stop),
one and only one of these must be specified.
This tolerance applies to any particular cartesian
component of any atom, INCLUDING fixed ones.
This is to be used when trying to equilibrate a
structure to its lowest energy configuration (ionmov=2),
or in case of molecular dynamics (ionmov=1)
A value ten times smaller
than tolmxf is suggested (for example 5.0d6 hartree/bohr).
This stopping criterion is not allowed for RF calculations.
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 Complete list of input variables
tolvrs
Mnemonics: TOLerance on the potential V(r) ReSidual
Characteristic:
Variable type: real parameter
Default is 0.0 (stopping condition ignored)
Sets a tolerance for potential
residual that, when reached, will cause one SCF cycle
to stop (and ions to be moved).
If set to zero, this stopping condition is ignored.
Effective only when SCF cycles are done (iscf>0).
In this case, since toldfe, toldff,
tolvrs and tolwfr
are aimed at the same goal (causing the SCF cycle to stop),
one and only one of these must be specified.
To get accurate stresses may be quite demanding.
Go to the top
 Complete list of input variables
tolwfr
Mnemonics: TOLerance on WaveFunction squared Residual
Characteristic:
Variable type: real parameter
Default is 0.0d0 (stopping criterion ignored)
Gives a convergence tolerance for the
largest squared "residual" (defined below) for any
given band. The squared residual is:
< nk(HE)^{2}nk >, E = < nkHnk >,
which clearly is nonnegative and goes to 0 as
the iterations converge to an eigenstate.
With the squared residual expressed in
Hartrees^{2} (Hartrees squared), the largest squared
residual (called residm) encountered over all bands
and k points must be less than tolwfr for iterations
to halt due to successful convergence.
Note that if iscf>0, this criterion should be replaced
by those based on toldfe (preferred for ionmov==0),
toldff (preferred for ionmov/=0) or
tolvrs (preferred for theoretical reasons!).
When tolwfr is 0.0, this criterion is ignored,
and a finite value of toldfe, toldff
or tolvrs must be specified.
This also imposes a restriction
on taking an ion step; ion steps are not permitted
unless the largest squared residual is less than
tolwfr, ensuring accurate forces.
To get accurate stresses may be quite demanding.
Note that the preparatory GS calculations
before a RF calculations must be highly converged.
Typical values for these preparatory runs are tolwfr
between 1.0d16 and 1.0d22.
Note that tolwfr is often used in the test cases, but this is
tolwfr purely for historical reasons :
except when iscf<0, other critera should be used.
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 Complete list of input variables
typat
Mnemonics: TYPE of atoms
Characteristic:
Variable type: integer array typat(natom)
(or : typat(natrd) ,
if the geometry builder is used)
Default is 1 (for natom=1)
Array giving an integer label to every atom in the unit
cell to denote its type.
The different types of atoms
are constructed from the pseudopotential files.
There are at most ntypat types of atoms.
As an example, for BaTiO3, where the pseudopotential for Ba is number 1,
the one of Ti is number 2, and the one of O is number 3, the actual
value of the typat array might be :
typat 1 2 3 3 3
The array typat has to agree with the actual locations
of atoms given in xred , xcart or
xangst, and the input
of pseudopotentials has to be ordered to agree with the
atoms identified in typat.
The nuclear charge of the
elements, given by the array znucl, also must agree with
the type of atoms designated in "typat".
The array typat is
not constrained to be increasing. An
internal representation of the list of atoms,
deep in the code (array atindx), groups the atoms of same type
together. This should be transparent to the
user, while keeping efficiency.
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 Complete list of input variables
udtset
Mnemonics: Upper limit on DaTa SETs
Characteristic:
Variable type: integer array udtset(2)
No Default (since it is not used when it is not defined).
Used to define the set of indices in the multidata set
mode, when a double loop is needed (see later).
The values of udtset must be between 1 and 9, and their
product must be equal to ndtset.
If udtset is used, the input variable jdtset cannot be used.
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 Complete list of input variables
wtk
Mnemonics: WeighTs for K points
Characteristic:
Variable type: real array wtk(nkpt)
Default value is nkpt*1.0d0 .
Gives the k point weights.
The
k point weights will have their sum normalized to 1
(unless occopt=2; see description of occopt)
within the program and therefore may be input with any
arbitrary normalization. This feature helps avoid the
need for many digits in representing fractional weights
such as 1/3.
wtk is ignored if iscf is not positive,
except if iscf=3.
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 Complete list of input variables
xangst
Mnemonics: vectors (X) of atom positions
in cartesian coordinates length in ANGSTrom
Characteristic: NOT INTERNAL
Variable type: real array xangst(3,natom)
(or xangst(3,natrd) if the geometry builder is used)
Gives the cartesian coordinates
of atoms within unit cell, in angstrom. This information is
redundant with that supplied by array xred or xcart.
If xred and xangst are ABSENT from the input file and
xcart is
provided, then the values of xred will be computed from
the provided xcart (i.e. the user may use xangst instead
of xred or xcart to provide starting coordinates).
One and only one of xred, xcart
and xangst must be provided.
The conversion factor between Bohr and Angstrom
is 1 Bohr=0.5291772083 Angstrom (See Physics Today August 1989 p.8).
Atomic positions evolve if ionmov/=0 .
In constrast with xred and
xcart, xangst is not internal.
Go to the top
 Complete list of input variables
xcart
Mnemonics: vectors (X) of atom positions in CARTesian coordinates
Characteristic: EVOLVING, LENGTH
Variable type: real array xcart(3,natom)
(or xcart(3,natrd) if the geometry builder is used)
Gives the cartesian coordinates
of atoms within unit cell. This information is
redundant with that supplied by array xred or xangst.
By default, xcart is given in bohr atomic units
(1 bohr=0.5291772083 Angstroms), although Angstrom can be specified,
if preferred, since xcart has the
'LENGTH' characteristics.
If xred and xangst are
ABSENT from the input file and xcart is
provided, then the values of xred will be computed from
the provided xcart (i.e. the user may use xcart instead
of xred or xangst to provide starting coordinates).
Atomic positions evolve if ionmov/=0 .
Go to the top
 Complete list of input variables
xred
Mnemonics: vectors (X) of atom positions in REDuced coordinates
Characteristic: EVOLVING
Variable type: real array xred(3,natom)
(or xred(3,natrd) if the geometry builder is used)
Default to all 0.0d0
Gives the atomic locations within
unit cell in coordinates relative to real space primitive
translations (NOT in cartesian coordinates). Thus these
are fractional numbers typically between 0 and 1 and
are dimensionless. The cartesian coordinates of atoms
are given by:
t_cartesian = t1*r1*a1+t2*r2*a2+t3*r3*a3
where (t1,t2,t3) are the "reduced coordinates" given in
columns of "xred", (r1,r2,r3) are the columns of
dimensionless array "rprim", and (a1,a2,a3) are the
elements of the array "acell" giving length scales in bohr.
If you prefer to work only with cartesian coordinates, you
may work entirely with "xcart" or "xangst" and ignore xred, in
which case xred must be absent from the input file.
One and only one of xred, xcart and
and xangst must be provided.
Atomic positions evolve if ionmov/=0 .
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 Complete list of input variables
znucl
Mnemonics: charge Z of the NUCLeus
Characteristic: NO MULTI
Variable type: real array znucl(npsp)
Gives nuclear charge for each
type of pseudopotential, in order.
If znucl does not agree with nuclear charge,
as given in pseudopotential files, the program writes
an error message and stops.
N.B. : In the pseudopotential files, znucl is called "zatom".
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 Complete list of input variables
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