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) 1998-2014 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.


A.
B. bdeigrf  
C.
D.
E. elph2_imagden   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   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.



Go to the top | Complete list of input variables



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

Only relevant if ieig2rf = 1, 2, 3 or 4 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.




Go to the top | Complete list of input variables



elph2_imagden

Mnemonics: ELectron-PHonon interaction at 2nd order : IMAGina y shoft of the DENominator
Characteristic: RESPFN,'ENERGY'
Variable type: real parameter
Default is 0.0 Ha.

Only relevant if ieig2rf is non-zero, that is, if the user is performing performing second-order eigenvalue calculations using response-functions.

The variable elph2_imagden determines the imaginary shift of the denominator of the sum-over-states in the perturbation denominator, (e_{nk}-e_{n'k'}+i elph2_imagden). 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)




Go to the top | Complete list of input variables



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)




Go to the top | Complete list of input variables



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 (Sternheimer).
If ieig2rf is set to 2, the second-order electronic eigenvalues will be calculated from the Allen-Cardona method. (sum over states)
If ieig2rf is set to 3, the second-order electronic eigenvalues will be calculated from the DFPT method (sum over states) but using a different part of the code. This is equivalent to ieig2rf = 1 [debuging]
If ieig2rf is set to 4, the second-order electronic eigenvalues will be calculated from the dynamical DFPT method (Sternheimer).
Related variables : bdeigrf,elph2_imagden,getgam_eig2nkq,smdelta




Go to the top | Complete list of input variables



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.




Go to the top | 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 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.




Go to the top | Complete list of input variables



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.



Go to the top | Complete list of input variables



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).



Go to the top | Complete list of input variables



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 charges and dynamical matrix at Gamma within a response function calculation (not active at the level of producing the DDB, but at the level of the phonon eigenfrequencies output).

The treatment of the acoustic sum rule and charge neutrality sum rule is finer at the level of the ANADDB utility, with the two independent input variables asr and chneut.




Go to the top | Complete list of input variables

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, denoting perturbations of electric field or stress type (see the response function help file).




Go to the top | Complete list of input variables



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 in the electric field calculations (see rfelfd) The directions for the derivatives are determined by rfdir.





Go to the top | 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 (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).




Go to the top | 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.
Only rfelfd is compatible with both norm-conserving pseudopotentials as well as PAW. Higher mixed perturbations can be used only with norm-conserving pseudopotentials.

(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).




Go to the top | Complete list of input variables

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.



Go to the top | Complete list of input variables



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.



Go to the top | 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.

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




Go to the top | Complete list of input variables

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.

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.



Go to the top | 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 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.




Go to the top | Complete list of input variables



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:




Go to the top | Complete list of input variables

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.




Go to the top | Complete list of input variables



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.




Go to the top | Complete list of input variables