ABINIT, GW input variables:
List and description.
This document lists and provides the description
of the name (keywords) of the GW 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,
then the abinis help file,
before reading the present file. It will be easier to discover the
present file with the help of the lesson 6 of the tutorial
Other input variables directly related to the GW computation are :
getkss
getscr
optdriver.
Copyright (C) 2002-2004 ABINIT group (XG)
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 .
Goto :
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Help files :
New user's guide
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Mrgddb
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Anaddb
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Cut3D
Files that describe other input variables:
- Basic variables, VARBAS
- Developper variables, VARDEV
- File handling variables, VARFIL
- Geometry builder + symmetry related variables, VARGEO
- Ground-state calculation variables, VARGS
- Internal variables, VARINT
- Parallelisation variables, VARPAR
- Projector-Augmented Wave variables, VARPAW
- Response Function variables, VARRF
- Structural optimization variables, VARRLX
Content of the file : alphabetical list of variables.
A.
B.
bdgw
C.
D.
E.
ecuteps
ecutsigx
ecutwfn
F.
G.
gwcalctyp
H.
I.
J.
K.
kptgw
M.
N.
nbandkss
npwkss
nkptgw
nomegasrd
npweps
npwsigx
npwwfn
nsheps
nshsigx
nshwfn
O.
omegasrdmax
P.
ppmfrq
Q.
R.
S.
soenergy
T.
U.
V.
W.
X.
Y.
Z.
zcut
bdgw
Mnemonics: BanDs for GW calculation
Characteristic: GW
Variable type: integer bdgw(2,nkptgw)
Default is all 0's
For each k-point with number igwpt in the range (1:nkptgw),
bdgw(1,igwpt) is the
number of the lowest band for which the GW computation must be done,
and bdgw(2,igwpt) is the number of the highest band for
which the GW computation must be done.
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ecuteps
Mnemonics: Energy CUT-off for EPSilon (the dielectric matrix)
Characteristic: GW
Variable type: real
Default: 0.0
Only relevant if optdriver=3,
that is, GW calculations.
ecuteps determines the
cut-off energy of the planewave set used to represent
the independent-particle susceptibility $\chi^{(0)}_{KS}$,
the dielectric matrix $\epsilon$, and its inverse.
It is not worth to take ecuteps bigger
than four times ecutwfn,
this latter limit corresponding to the highest Fourier
components of a wavefunction convoluted with itself.
Usually, even twice the value of ecutwfn
might overkill. In any case, a convergence study is worth.
This set of planewaves can also be determined by the other input variables
npweps and nsheps,
but these are much less convenient to use for general systems, than the
selection criterion based on a cut-off energy.
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ecutsigx
Mnemonics: Energy CUT-off for MAT ??
Characteristic: GW
Variable type: real
Default: 0.0
Only relevant if optdriver=4,
that is, GW calculations. This input variable was named "ecutmat"
prior to v4.3 .
ecutsigx determines the
cut-off energy of the planewave set used to generate the
exchange part of the self-energy operator.
This set of planewaves can also be determined by the other input variables
npwsigx and nshsigx,
but these are much less convenient to use for general systems, than the
selection criterion based on the cut-off energy.
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ecutwfn
Mnemonics: Energy CUT-off for WaveFunctions
Characteristic: GW
Variable type: real
Default: 0.0
Only relevant if optdriver=3 or 4,
that is, GW calculations.
ecutwfn determines the
cut-off energy of the planewave set used to represent the wavefunctions
in the formula that generates the independent-particle susceptibility $\chi^{(0)}_{KS}$
(for optdriver=3), or the
self-energy (for optdriver=4).
Usually, ecutwfn is smaller than ecut,
so that the wavefunctions are filtered, and some components are ignored.
As a side effect, the wavefunctions are no more normalized, and also,
no more orthogonal.
Also, the set of plane waves can be much smaller for
optdriver=3,
than for
optdriver=4, although a convergence
study is needed to choose correctly both values.
This set of planewaves can also be determined by the other input variables
npwwfn and nshwfn,
but these are much less convenient to use for general systems, than the
selection criterion based on the cut-off energy.
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gwcalctyp
Mnemonics: GW CALCulation TYPe
Characteristic: GW
Variable type: integer
Default: 0
Only relevant if optdriver=3 or 4,
that is, GW calculations.
gwcalctyp governs the choice between plasmon-pole
approximation or full integration, or ... (to be described),
for development purposes.
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kptgw
Mnemonics: K-PoinTs for GW calculations
Characteristic: GW
Variable type: real kptgw(3,nkptgw)
Default: all 0.0's
For each k-point with number igwpt in the range (1:nkptgw),
kptgw(1,igwpt) is the reduced coordinate of the k-point.
At present, not all k-points are possible. Only those corresponding to the k-point
grid defined
with the same repetition parameters
(kptrlatt,
or ngkpt)
than the GS one, but WITHOUT any shift, are allowed.
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nbandkss
Mnemonics:
Number of BaNDs STOred
Characteristic:
Variable type: integer parameter
Default is 0
This input variable (also called "nbndsto" prior to v4.3) is used for the preparation of a GW calculation :
it will be used in a GS run (where optdriver=0)
to generate a _KSS file. In this run, nbandkss should be non-zero.
Then, this GS run
should be followed with a run where
optdriver=3.
- If nbandkss=0, no _KSS file is created
- If nbandkss=-1, all the available eigenstates (energies
and eigenfunctions) are stored in a abo_KSS file at the end of the
ground state calculation. The number of states is forced to be
the same for all k-points : it will be the minimum of the number
of plane waves over all k-points.
- If nbandkss is greater than 0, abinit stores (about)
nbandkss eigenstates in a abo_KSS file. This number of states
is forced to be the same for all k-points.
See npwkss for the selection
of the number of the planewave components of the eigenstates
to be stored.
Very important : for the time being, istwfk
must be 1 for all the k-points.
For more details about the format of the abo_KSS file, see
the routine outkss.f .
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npwkss
Mnemonics:
Number of planewave COMponents STOred
Characteristic:
Variable type: integer parameter
Default is 0
This input variable (was called "ncomsto" prior to v4.3)
is used for the preparation of a GW calculation :
the GS run (where optdriver=1
and nbandkss/=0) should be followed with a run where
optdriver=3.
Also, if nbandkss=0,
no use of npwkss.
npwkss
defines the number of planewave components of the Kohn-Sham states
to build the Hamiltonian, in the routine outkss.f,
and so, the size of the matrix, the size of eigenvectors,
and the number of available states,
to be stored in the abo_KSS file.
If it is set to 0, then, the planewave basis set defined by
the usual Ground State input variable ecut
is used to generate the superset of all planewaves used for all k-points.
Note that this (large) planewave basis is the
same for all k-points.
Very important : for the time being, istwfk
must be 1 for all the k-points.
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nkptgw
Mnemonics: Number of GW PoinTs
Characteristic: GW
Variable type: integer
Default: 0
Only relevant if optdriver=4,
that is, GW calculations. This input variable was called "ngwpt"
in versions before v4.3 .
nkptgw gives the number of k-points for which the GW calculation must be done.
It is used to dimension kptgw
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nomegasrd
Mnemonics: Number of OMEGA to evaluate the Sigma Real axis Derivative
Characteristic: GW
Variable type: integer
Default: 9
Only relevant if optdriver=4,
that is, GW calculations.
The number of frequencies omega where sigma is calculation
around the KS energy on the real axis. From these values, the
derivative of Sigma with respect to omega and calculated
at the KS energy is evaluated.
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npweps
Mnemonics: Number of PlaneWaves for EPSilon (the dielectric matrix)
Characteristic: GW
Variable type: integer
Default: 0
Only relevant if optdriver=3,
that is, GW calculations.
npweps determines the
size of the planewave set used to represent
the independent-particle susceptibility $\chi^{(0)}_{KS}$,
the dielectric matrix $\epsilon$ and its inverse.
See ecuteps
(preferred over npweps) for more information.
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npwsigx
Mnemonics: Number of PlaneWaves for SIGma eXchange
Characteristic: GW
Variable type: integer
Default: 0
Only relevant if optdriver=4,
that is, GW calculations. This input variable wxas previously
called "npwmat".
npwsigx determines the
cut-off energy of the planewave set used to generate the
exchange part of the self-energy operator.
See ecutsigx
(preferred over npwsigx) for more information.
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npwwfn
Mnemonics: Number of PlaneWaves for WaveFunctioNs
Characteristic: GW
Variable type: integer
Default: 0
Only relevant if optdriver=3 or 4,
that is, GW calculations.
npwwfn determines the
size of the planewave set used to represent the wavefunctions
in the formula that generates the independent-particle susceptibility $\chi^{(0)}_{KS}$.
See ecutwfn
(preferred over nshwfn) for more information.
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nsheps
Mnemonics: Number of SHells for EPSilon (the dielectric matrix)
Characteristic: GW
Variable type: integer
Default: 0
Only relevant if optdriver=3,
that is, GW calculations.
nsheps determines the
size of the planewave set used to represent
the independent-particle susceptibility $\chi^{(0)}_{KS}$,
the dielectric matrix $\epsilon$ and its inverse.
See ecuteps
(preferred over nsheps) for more information.
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nshsigx
Mnemonics: Number of SHells for MAT ??
Characteristic: GW
Variable type: integer
Default: 0
Only relevant if optdriver=4,
that is, GW calculations.This input variable was named "nshma" prior to v4.3 .
nshsigx determines the
cut-off energy of the planewave set used to generate the
exchange part of the self-energy operator.
See ecutsigx
(preferred over nshsigx) for more information.
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nshwfn
Mnemonics: Number of SHells for WaveFunctioNs
Characteristic: GW
Variable type: integer
Default: 0
Only relevant if optdriver=3 or 4,
that is, GW calculations.
nshwfn determines the
number of shells of the planewave set used to represent the wavefunctions
in the formula that generates the independent-particle susceptibility $\chi^{(0)}_{KS}$.
See ecutwfn (preferred over nshwfn)
for more information.
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omegasrdmax
Mnemonics: OMEGA to evaluate the Sigma Real axis Derivative : MAXimal value
Characteristic: GW
Variable type: real
Default: 1.0 eV
Only relevant if GW calculations.
The maximum distance from the KS energy where to evaluate Sigma.
Sigma is evaluated at [KS_energy - maxomegasrd, KS_energy + maxomegasrd]
sampled nomegasrd times.
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ppmfrq
Mnemonics: Plasmon Pole Model FReQuency
Characteristic: ENERGY, GW
Variable type: real
Default: 0.0 Ha
(This input variable was named plasfrq prior to v4.3).
Only relevant if optdriver=3,
that is, GW calculations.
The present GW implementation is based on a plasmon-pole model.
In this plasmon-pole model, the screening must be available
at zero frequency, as well as at another frequency, imaginary,
on the order of the plasmon frequency (the peak in the EELS
spectrum). This information is used to derive the
behaviour of the dielectric matrix for all the frequencies (complex).
ppmfrq defines the imaginary frequency at which
the dielectric matrix is evaluated, in addition to the zero
frequency. If the plasmon-pole approximation is good, then, the
choice of ppmfrq should have no influence on the
final result. One should check whether this is the case.
In general, the plasmon frequencies of bulk solids are on the
order of 0.5 Hartree.
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soenergy
Mnemonics: Scissor Operator ENERGY
Characteristic: GW, ENERGY
Variable type: real
Default: 0.0
Only relevant if optdriver=3,
that is, GW calculations of screening.
The Scissor operator energy to be added to unoccupied levels for the
screening calculation. In some cases, it mimics a second iteration
self-consistent GW calculation.
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zcut
Mnemonics: Z-CUT
Characteristic: GW , ENERGY
Variable type: real
Default: 0.1 eV =3.67493260d-03Ha
Only relevant if optdriver=4,
that is, GW calculations.
It is meant to avoid some divergencies that might
occur due to the numerical treatment of integrable poles along the integration path.
If the denominator becomes smaller than zcut, a small imaginary part
(depending on zcut) is added, in order to avoid the divergence.
Ideally, one should make a convergence study of zcut decreasing for
increasing number of k-points.
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| Complete list of input variables
Goto :
ABINIT home Page
|
Welcome
|
Suggested acknowledgments
|
List of input variables
|
Tutorial home page
|
Bibliography
Help files :
New user's guide
|
Abinis (main)
|
Abinis (respfn)
|
Mrgddb
|
Anaddb
|
AIM (Bader)
|
Cut3D