This document lists and provides the description of the name (keywords) of the response function 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 response-function calculations using abinis, the complementary file ~ABINIT/Infos/respfn_help is needed.

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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Help files :

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
- GW variables, VARGW
- Internal variables, VARINT
- Parallelisation variables, VARPAR
- Projector-Augmented Wave variables, VARPAW
- Structural optimization variables, VARRLX

A.

B.

C.

D. dsifkpt

E.

F.

G.

H.

I.

J.

K.

M. mkqmem mk1mem

N.

O.

P. prepanl prtbbb

Q.

R. rfasr rfatpol rfdir rfelfd rfphon rfstrs rfthrd rfuser rf1atpol rf1dir rf1elfd rf1phon rf2atpol rf2dir rf2elfd rf2phon rf3atpol rf3dir rf3elfd rf3phon

S. sciss

T. td_maxene td_mexcit

U.

V.

W.

X.

Y.

Z.

dsifkpt

Mnemonics: DenSiFy K-PoinTs

Characteristic:

Variable type: integer array dsifkpt(3)

Default is 1.

Can be used to density the k point grid along the lines that are parallel to the three primitive vectors, in reciprocal space. Should be useful for third-order derivatives that include some derivative with respect to k-points or electric field. This part is in development. For the time being, consult ~ABINIT/Infos/nonlinear.ps

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mkqmem

Mnemonics: Maximum number of K+Q - points in MEMory

mk1mem

Mnemonics: Maximum number of K - points for
1st order wavefunctions, kept in MEMory

Characteristic: RESPFN

Variable type: integer parameters

Default is nkpt, i.e. in-core solution.

Plays a role similar to mkmem
but for different sets of wavefunctions : the
ground state wavefunctions at k+q and the first-order
wavefunctions. Only needed for response calculations.

Internal representation as mkmems(2) and mkmems(3).

Note (991019) that although the effective number of k points
can be reduced thanks to symmetry for different
perturbations, **mkqmem** and **mk1mem** are presently
still compared with the input nkpt. This should be changed
later.

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** | **Complete list of input variables

prepanl

Mnemonics: PREPAre Non-Linear response calculation

Characteristic: RESPFN

Variable type: integer parameter

Default is 0.

The computation of third-order derivatives from the 2n+1 theorem requires the first-order wavefunctions and densities obtained from a linear response calculation. The standard approach in a linear response calculation is (i) to compute only the irreductible perturbations, and (ii) to use symmetries to reduce the number of k-points for the k-point integration.

This approach cannot be applied, presently (v4.1), if the first-order wavefunctions are to be used to compute third-order derivatives. First, for electric fields, the code needs the derivatives along the three directions. Still, in case of phonons, only the irreducible perturbations are required. Second, for both electric fields and phonons, the wavefunctions must be available in half the BZ (kptopt=2), or the full BZ (kptopt=3).

During the linear response calculation, in order to prepare a non-linear calculation, one should put

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prtbbb

Mnemonics: PRinT Band-By-Band decomposition

Characteristic: RESPFN

Variable type: integer parameter

Default is 0.

If

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rfasr

Mnemonics: Response Function : Acoustic Sum Rule

Characteristic: RESPFN

Variable type: integer parameter

Default is 0.

Control the evaluation of the acoustic sum rule in effective charge calculations within a response function calculation.

- 0 => no acoustic sum rule imposed
- 1 => acoustic sum rule imposed with extra charge evenly distributed among atoms
- 2 => acoustic sum rule imposed with extra charge given proportionally to those atoms with the largest effective charge.

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rfatpol

Mnemonics: Response Function : limits of ATomic POLarisations

Characteristic: RESPFN

rf1atpol

Mnemonics: non-linear Response Function, 1st mixed perturbation : limits of ATomic POLarisations

Characteristic: NON-LINEAR

rf2atpol

Mnemonics: non-linear Response Function, 2nd mixed perturbation : limits of ATomic POLarisations

Characteristic: NON-LINEAR

rf3atpol

Mnemonics: non-linear Response Function, 3rd mixed perturbation : limits of ATomic POLarisations

Characteristic: NON-LINEAR

Variable type: integer array of 2 elements

Default is 1 1

Control the range
of atoms for which displacements will be considered
in phonon calculations (atomic polarisations), or in non-linear
computations, using the 2n+1 theorem.

These values are only relevant to phonon response function
calculations, or non-linear computations.

May take values from 1 to natom, with **rfatpol**(1)<=**rfatpol**(2).

The atoms to be moved will be defined by the

do-loop variable iatpol :

do iatpol=**rfatpol**(1),**rfatpol**(2)

For the calculation of a full dynamical matrix, use
**rfatpol**(1)=1 and **rfatpol**(2)=natom, together with
rfdir 1 1 1 . For selected elements of the
dynamical matrix, use different values of **rfatpol** and/or
rfdir. The name 'iatpol' is used for the part of the
internal variable ipert when it runs from 1 to natom. The
internal variable ipert can also assume values larger
than natom, of electric field or stress type (see respfn.help).

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** | **Complete list of input variables

rfdir

Mnemonics: Response Function : DIRections

Characteristic: RESPFN

rf1dir

Mnemonics: non-linear Response Function, 1st mixed perturbation : DIRections

Characteristic: NON-LINEAR

rf2dir

Mnemonics: non-linear Response Function, 2nd mixed perturbation : DIRections

Characteristic: NON-LINEAR

rf3dir

Mnemonics: non-linear Response Function, 3rd mixed perturbation : DIRections

Characteristic: NON-LINEAR

Variable type: integer array of 3 elements

Default is 0 0 0.

Gives the directions
to be considered for response function calculations, or non-linear computations.

The three elements corresponds to the three primitive
vectors, either in real space (phonon calculations),
or in reciprocal space (d/dk and homogeneous electric field
calculations). So, they generate a basis
for the generation of the dynamical matrix or
to macroscopic didlectric tensor, of the effective
charge tensors.

If equal to 1, response functions, as defined
by rfelfd, rfphon, **rfdir**
and rfatpol, are to be computed
for the corresponding direction. If 0, this direction
should not be considered (for non-linear computations, the corresponding input
variables should be used).

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** | **Complete list of input variables

rfelfd

Mnemonics: Response Function with respect to the ELectric FielD

Characteristic: RESPFN

rf1elfd

Mnemonics: non-linear Response Function, 1st mixed perturbation : ELectric FielD

Characteristic: NON-LINEAR

rf2elfd

Mnemonics: non-linear Response Function, 2nd mixed perturbation : ELectric FielD

Characteristic: NON-LINEAR

rf3elfd

Mnemonics: non-linear Response Function, 3rd mixed perturbation : ELectric FielD

Characteristic: NON-LINEAR

Variable type: integer parameter

Default is 0.

Turns on electric field response
function calculations (or non-linear computation, including the electric field
perturbation). Actually, such calculations
requires first the non-self-consistent calculation
of derivatives with respect to k, independently of the
electric field perturbation itself.

- 0=>no electric field perturbation
- 1=>full calculation, with first the derivative of ground-state wavefunction with respect to k (d/dk calculation), by a non-self-consistent calculation, then the generation of the first-order response to an homogeneous electric field
- 2=>only the derivative of ground-state wavefunctions with respect to k
- 3=>only the generation of the first-order response to the electric field, assuming that the data on derivative of ground-state wavefunction with respect to k is available on disk.

The options 2 and 3 proves useful in that context ; also, in case a scissor shift is to be used, it is usually not applied for the d/dk response).

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rfmeth

Mnemonics: Response Function METHod

Characteristic: RESPFN

Variable type: integer parameter

Default is 1.

Selects method used in response function calculations. Presently, only 1 is allowed.

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rfphon

Mnemonics: Response Function with respect to PHONons

Characteristic: RESPFN

rf1phon

Mnemonics: non-linear Response Function, 1st mixed perturbation : PHONons

Characteristic: NON-LINEAR

rf2phon

Mnemonics: non-linear Response Function, 2nd mixed perturbation : PHONons

Characteristic: NON-LINEAR

rf3phon

Mnemonics: non-linear Response Function, 3rd mixed perturbation : PHONons

Characteristic: NON-LINEAR

Variable type: integer parameter

Default is 0.

It must be equal to 1
to run phonon response function calculations, or to include some phonon perturbation
in non-linear computations.

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** | **Complete list of input variables

rfstrs

Mnemonics: Response Function with respect to STRainS

Characteristic: RESPFN

Variable type: integer parameter

Default is 0.

Used to run strain response-function calculations (e.g. needed to get elastic constants). Define, with rfdir, the set of perturbations.

- 0=>no strain perturbation
- 1=>only uniaxial strain(s) (ipert=natom+3 is activated)
- 2=>only shear strain(s) (ipert=natom+4 is activated)
- 3=>both uniaxial and shear strain(s) (both ipert=natom+3 and ipert=natom+4 are activated)

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rfthrd

Mnemonics: Response Function of THiRD order

Characteristic: RESPFN

Variable type: integer parameter

Default is 0.

Used to control response function calculation of third order response.

Not implemented.

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rfuser

Mnemonics: Response Function, USER-defined

Characteristic: RESPFN

Variable type: integer parameter

Default is 0.

Available to the developpers, to activate the use of ipert=natom+5 and ipert=natom+6, two sets of perturbations that the developpers can define.

- 0=>no computations for ipert=natom+5 or ipert=natom+6
- 1=>response with respect to perturbation natom+5 will be computed
- 2=>response with respect to perturbation natom+6 will be computed
- 3=>responses with respect to perturbations natom+5 and natom+6 will be computed

In order to define and use correctly the new perturbations,
the developper might have to include code lines or additional routines
at the level of the following routines :
cgwf3.f, chkph3.f, dyout3.f, d2sym3.f, eneou3.f, eneres3.f, gath3.f, insy3.f,
loper3.f, mkcor3.f, nstdy3.f, nstwf3.f, respfn.f,
scfcv3.f, syper3.f, vloca3.f, vtorho3.f, vtowfk3.f, wings3.f, .
In these routines, the developper should pay a particular
attention to the rfpert array, defined in the routine respfn.f ,
as well as to the ipert local variable.

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** | **Complete list of input variables

sciss

Mnemonics: SCISSor operator

Characteristic: RESPFN, ENERGY

Variable type: real parameter

Default is 0.

It is the value of the "scissors operator", the shift of conduction band eigenvalues, used in response function calculations.

Can be specified in Ha (the default), Ry, eV or Kelvin, since

Typical use is for response to electric field (rfelfd=3), but NOT for d/dk (rfelfd=2) and phonon responses.

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td_maxene

Mnemonics: Time-Dependent dft : MAXimal kohn-sham ENErgy difference

Characteristic: TDDFT

Variable type: real parameter

Default is huge.

The Matrix to be diagonalized in the Casida framework (see "Time-Dependent Density Functional Response Theory of Molecular systems: Theory, Computational Methods, and Functionals", by M.E. Casida, in Recent Developments and Applications of Modern Density Functional Theory, edited by J.M. Seminario (Elsevier, Amsterdam, 1996).) is a NxN matrix, where, by default, N is the product of the number of occupied states by the number of unoccupied states.

The input variable

See td_mexcit for an alternative way to decrease N.

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td_mexcit

Mnemonics: Time-Dependent dft : Maximal number of EXCITations

Characteristic: TDDFT

Variable type: real parameter

Default is 0.

The Matrix to be diagonalized in the Casida framework (see "Time-Dependent Density Functional Response Theory of Molecular systems: Theory, Computational Methods, and Functionals", by M.E. Casida, in Recent Developments and Applications of Modern Density Functional Theory, edited by J.M. Seminario (Elsevier, Amsterdam, 1996).) is a NxN matrix, where, by default, N is the product of the number of occupied states by the number of unoccupied states.

The input variable

See td_maxene for an alternative way to decrease N.

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