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.
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.
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)
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)
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
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.
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.
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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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.
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.
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).
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).
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
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.
Variable type: integer array of 2 elements
Default is 1 1
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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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.
Variable type: integer parameter
Default is 0.
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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
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).
Variable type: integer array of 3 elements
Default is 0 0 0.
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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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
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.
Variable type: integer parameter
Default is 0.
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).
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Selects method used in response function calculations. Presently, only 1 is allowed.
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
It must be equal to 1
to run phonon response function calculations, or to include some phonon perturbation
in non-linear computations.
Variable type: integer parameter
Default is 0.
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Used to run strain response-function calculations (e.g. needed to get elastic constants). Define, with rfdir, the set of perturbations.
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.
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.
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:
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.
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.