ABINIT, response function input variables:

List and description.

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 abinit 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/doc/users/tuning file might be useful. For response-function calculations using abinit, please read the response function help file

Copyright (C) 1998-2010 ABINIT group (DCA, XG, RC)
This file is distributed under the terms of the GNU General Public License, see ~abinit/COPYING or http://www.gnu.org/copyleft/gpl.txt .
For the initials of contributors, see ~abinit/doc/developers/contributors.txt .

Goto : ABINIT home Page | Suggested acknowledgments | List of input variables | Tutorial home page | Bibliography

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
Wannier90 interface variables, VARW90

Content of the file : alphabetical list of variables.

A.
B. bdeigrf
C.
D.
E. esmear
F. frzfermi
G.
H.
I. ieig2rf
J.
K.
M. mkqmem   mk1mem
N.
O.
P. prepanl   prepgkk   prtbbb
Q.
R. rfasr   rfatpol   rfddk   rfdir   rfelfd   rfmeth   rfmgfd   rfphon   rfstrs   rfuser   rf1atpol   rf1dir   rf1elfd   rf1phon   rf2atpol   rf2dir   rf2elfd   rf2phon   rf3atpol   rf3dir   rf3elfd   rf3phon
S. sciss   smdelta
T. td_maxene   td_mexcit
U.
V.
W.
X.
Y.
Z.

frzfermi
Mnemonics: FReeZe FERMI energy
Characteristic:
Variable type: integer parameter
Default is 0.

Can be used to suppress artificially the first-order change of Fermi energy, in case of Response Function calculation for metals at Q=0. This change is needed, but was not computed prior to v4.4 . Its calculation has been implemented by DHamann. The input variable frzfermi, if set to 1, allows to recover the previous, incorrect behaviour.

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bdeigrf
Mnemonics: BanD for second-order EIGenvalues from Response-Function
Characteristic: RESPFN
Variable type: integer parameters
Default is -1.

Only relevant if ieig2rf = 1 or 2, that is, if the user is performing second-order eigenvalue calculations using response-functions.

The variable bdeigrf is the maximum number of bands for which the second-order eigenvalues must be calculated: the full number of bands is still used during the computation of these corrections.

If bdeigrf is set to -1, the code will automatically set bdeigrf equal to nband.

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esmear
Mnemonics: Eigenvalue SMEARing
Characteristic: RESPFN,'ENERGY'
Variable type: real parameter
Default is 0.04 Ha.

Only relevant if smdelta = 1-5, that is, if the user is performing simulations of the electronic lifetimes induced by the electron-phonon coupling.

The variable esmear determines the width of the functions approximating the delta function, \delta(e_{nk}-e_{n'k'}), present in the expression of the lifetimes. One should use a width comparable with the Debye frequency or the maximum phonon frequency.
Can be specified in Ha (the default), Ry, eV or Kelvin, since ecut has the 'ENERGY' characteristics. (1 Ha=27.2113845 eV)

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ieig2rf
Mnemonics: Integer for second-order EIGenvalues from Response-Function
Characteristic: RESPFN
Variable type: integer parameters
Default is 0.

If ieig2rf is greater then 0, the code will produce a file, named with the trailing suffix _EIGR2D, containing the second-order electronic eigenvalues for the perturbation. These files are used in the calculation of the thermal correction to the electronic eigenvalues.

If ieig2rf is set to 1, the second-order electronic eigenvalues will be calculated from the DFPT method.
If ieig2rf is set to 2, the second-order electronic eigenvalues will be calculated from the Allen-Cardona method.

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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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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 irreducible 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 prepanl to 1 in order to force ABINIT (i) to compute the electric field perturbation along the three directions explicitly, and (ii) to keep the full number of k-points.

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prepgkk
Mnemonics: PREPAre GKK calculation
Characteristic: RESPFN
Variable type: integer parameter
Default is 0.

The calculation of electron-phonon coupling quantities requires the presence of all the perturbations (all atoms in all directions) for the chosen set of (irreducible) q-points. To impose this and prevent ABINIT from using symmetry to reduce the number of perturbations, set prepgkk to 1. Use in conjunction with prtgkk.

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prtbbb
Mnemonics: PRinT Band-By-Band decomposition
Characteristic: RESPFN
Variable type: integer parameter
Default is 0.

If prtbbb is 1, print the band-by-band decomposition of Born effective charges and localization tensor, in case they are computed. See Ph. Ghosez and X. Gonze, J. Phys.: Condens. Matter 12, 9179 (2000).

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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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rfddk
Mnemonics: Response Function with respect to Derivative with respect to K
Characteristic: RESPFN

Variable type: integer parameter
Default is 0.

Activates computation of derivatives of ground state wavefunctions with respect to wavevectors. This is not strictly a response function but is a needed auxiliary quantity for example in the electric field and magnetic field calculations (see rfelfd and rfmgfd). The directions for the derivatives are determined by rfdir.

0=>no derivative calculation

1=>calculation of first derivatives of wavefunctions with respect to k points (d/dk calculation). The exact same functionality is provided by rfelfd = 2 and rfmgfd = 2

2=>will activate second derivative calculation but this is NOT YET implemented.

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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 (also for the Berry phase computation of the polarization, see the berryopt input variable).
The three elements corresponds to the three primitive vectors, either in real space (phonon calculations), or in reciprocal space (d/dk, homogeneous electric field, homogeneous magnetic field calculations). So, they generate a basis for the generation of the dynamical matrix or the macroscopic dielectric tensor or magnetic susceptibility and magnetic shielding, or the effective charge tensors.
If equal to 1, response functions, as defined by rfddk, 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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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.
Only rfelfd is compatible with both norm-conserving pseudopotentials as well as PAW. Higher mixed perturbations can be used only with norm-conserving pseudopotentials.

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.

(Note : because the tolerances to be used for derivatives or homogeneous electric field are different, one often does the calculation of derivatives in a separate dataset, followed by calculation of electric field response as well as phonon.
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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rfmgfd
Mnemonics: Response Function with respect to the MaGnetic FielD
Characteristic: RESPFN

Variable type: integer parameter
Default is 0.

Turns on magnetic field response function calculations. Actually, such calculations requires first the non-self-consistent calculation of derivatives with respect to k, independently of the magnetic field perturbation itself. This response function is compatible with PAW only, not with norm-conserving pseudopotentials.

0 : no magnetic field perturbation

1 : compute both derivatives with respect to wavevectors and magnetic response. Not yet implemented.

2 : compute the derivative of ground-state wavefunctions with respect to k

3 : compute response to magnetic field, given availability of both ground state and derivative wavefunctions. Not yet implemented.

(Note : because the tolerances to be used for derivatives and homogeneous magnetic fields are different, one often does the calculation of derivatives in a separate dataset, followed by calculation of magnetic field response.
The options 2 and 3 proves useful in that context.

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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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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)

See the possible restrictions on the use of strain perturbations, in the respfn_help file.

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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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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 ecut has the 'ENERGY' characteristics. (1 Ha=27.2113845 eV)
Typical use is for response to electric field (rfelfd=3), but NOT for d/dk (rfelfd=2) and phonon responses.

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smdelta
Mnemonics: SMeared DELTA function
Characteristic: RESPFN
Variable type: integer parameter
Default is 0

When smdelta in non-zero, it will trigger the calculation of the imaginary part of the second-order electronic eigenvalues, which can be related to the electronic lifetimes. The delta function is evaluated using:

when smdelta == 1, Fermi-Dirac smearing : 0.25_dp/(cosh(xx/2.0_dp)**2
when smdelta == 2, Cold smearing by Marzari using the parameter a=-.5634 (minimization of the bump): exp(-xx2)/sqrt(pi) * (1.5d0+xx*(-a*1.5d0+xx*(-1.0d0+a*xx)))
when smdelta == 3, Cold smearing by Marzari using the parameter a=-.8165 (monotonic function in the tail): as 2 but different a
when smdelta == 4, 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 smdelta=2, with different a).
when smdelta == 5, Gaussian smearing : 1.0d0*exp(-xx**2)/sqrt(pi)

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td_maxene
Mnemonics: Time-Dependent dft : MAXimal kohn-sham ENErgy difference
Characteristic: TDDFT
Variable type: real parameter
Default is 0.0

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 td_maxene allows to diminish N : it selects only the pairs of occupied and unoccupied states for which the Kohn-Sham energy difference is less than td_maxene. The default value 0.0 means that all pairs are taken into account.
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 td_mexcit allows to diminish N : it selects the first td_mexcit pairs of occupied and unoccupied states, ordered with respect to increasing Kohn-Sham energy difference. However, when td_mexcit is zero, all pairs are allowed.
See td_maxene for an alternative way to decrease N.

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Goto : ABINIT home Page | Suggested acknowledgments | List of input variables | Tutorial home page | Bibliography

ABINIT, response function input variables:

List and description.

Copyright (C) 1998-2010 ABINIT group (DCA, XG, RC) This file is distributed under the terms of the GNU General Public License, see ~abinit/COPYING or http://www.gnu.org/copyleft/gpl.txt . For the initials of contributors, see ~abinit/doc/developers/contributors.txt .

Content of the file : alphabetical list of variables.

Copyright (C) 1998-2010 ABINIT group (DCA, XG, RC)
This file is distributed under the terms of the GNU General Public License, see ~abinit/COPYING or http://www.gnu.org/copyleft/gpl.txt .
For the initials of contributors, see ~abinit/doc/developers/contributors.txt .