# ABINIT, electron-phonon calculation input variables:

## List and description.

This document lists and provides the description of the name (keywords) of the "electron-phonon calculation" input variables to be used in the main input file of the abinit code.

##### Copyright (C) 1998-2017 ABINIT group (DCA,XG,RC,YG,FJ)

### Content of the file : alphabetical list of "electron-phonon calculation" variables.

A. asr
B.
C. chneut
D. ddb_ngqpt ddb_shiftq dipdip
E. eph_extrael eph_fermie eph_fsewin eph_fsmear eph_intmeth eph_mustar eph_ngqpt_fine eph_transport
F.
G.
H.
I.
J.
K.
L.
M.
N.
O.
P. ph_intmeth ph_ndivsm ph_nqpath ph_nqshift ph_qshift ph_smear ph_wstep prtphbands prtphdos prtphsurf
Q.
R.
S. symdynmat

asr
Mnemonics: Acoustic Sum Rule
Executable: abinit
Mentioned in topic: DFPT.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88]}.
Variable type: integer
Default is 1

Govern the imposition of the Acoustic Sum Rule (ASR) in phonon calculations. Same meaning as the corresponding anaddb variable.

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chneut
Mnemonics: CHarge NEUTrality treatment
Executable: abinit
Mentioned in topic: Phonons.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88]}.
Variable type: integer
Default is 0

Set the treatment of the Charge Neutrality requirement for the effective charges. Same meaning as the corresponding anaddb variable.

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ddb_ngqpt
Mnemonics: Derivative DataBase: Number of Grid points for Q-PoinTs
Executable: abinit
Mentioned in topic: ElPhonInt.
Rarely used: [4/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88,89],v8:[44,65]}.
Variable type: integer(3)
Default is [0, 0, 0]

This variable is mandatory when optdriver==7. It defines the number of divisions in the (homogeneous) q-mesh used to generate the DDB file. See also the description of the getddb input variable.

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ddb_shiftq
Mnemonics: Derivative DataBase: SHIFT of the Q-points
Executable: abinit
Mentioned in topic: ElPhonInt.
Rarely used: [2/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[89],v8:[65]}.
Variable type: real(3)
Default is [0.0, 0.0, 0.0]

Only relevant when optdriver==7. It defines the shift in the q-mesh used to generate the DDB file, which is defined by the ddb_ngqpt input variable. See shiftk for more information on the definition.

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dipdip
Mnemonics: DIPole-DIPole interaction
Executable: abinit
Mentioned in topic: Phonons.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88]}.
Variable type: integer
Default is 1

This variable defines the treatment of the dipole-dipole interaction. Same meaning as the corresponding anaddb variable dipdip@anaddb

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eph_extrael
Mnemonics: Electron-PHonon: EXTRA ELectrons
Executable: abinit
Mentioned in topic: ElPhonInt.
Rarely used: [0/907] in abinit tests, [0/136] in tuto abinit tests.
Variable type: real
Default is 0.0

Number of electrons per unit cell to be added to the initial value computed from the pseudopotentials and unit cell.

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eph_fermie
Mnemonics: Electron-PHonon: FERMI Energy
Executable: abinit
Characteristic: ENERGY
Mentioned in topic: ElPhonInt.
Rarely used: [0/907] in abinit tests, [0/136] in tuto abinit tests.
Variable type: real
Default is 0.0

This variable can be used to change the value of the Fermi level when performing electron-phonon calculations with optdriver==7. This variable has effect only if set to a non-zero value. See also eph_extrael.

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eph_fsewin
Mnemonics: Electron-Phonon: Fermi Surface Energy WINdow
Executable: abinit
Characteristic: ENERGY
Mentioned in topic: ElPhonInt.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88]}.
Variable type: real
Default is 0.01 Hartree

This variable defines the energy window around the Fermi level used for e-ph calculations (optdriver = 7). Only the states located in the energy range [efermi - eph_fsewin, efermi + eph_fsewin] are included in the e-ph calculation.

Related input variables: eph_intmeth, eph_fsmear, eph_extrael and eph_fermie.

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eph_fsmear
Mnemonics: Electron-PHonon: Fermi surface SMEARing
Executable: abinit
Characteristic: ENERGY
Mentioned in topic: ElPhonInt.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88]}.
Variable type: real
Default is 0.01 Hartree
Only relevant if eph_intmeth == 1

This variable defines the gaussian broadening used for the integration over the Fermi surface when eph_intmeth == 1.

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eph_intmeth
Mnemonics: Electron-Phonon: INTegration METHod
Executable: abinit
Mentioned in topic: ElPhonInt.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88]}.
Variable type: integer
Default is 2

This variable defines the technique for the integration on the Fermi surface of electron-phonon quantities.

1 for Gaussian technique with broadening factor eph_fsmear. 2 for tetrahedron method.

See also eph_fsewin, eph_extrael and eph_fermie.
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eph_mustar
Mnemonics: Electron-PHonon : MU STAR (electron-electron interaction strength)
Executable: abinit
Mentioned in topic: ElPhonInt.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88]}.
Variable type: real
Default is 0.1

Average electron-electron interaction strength, for the computation of the superconducting Tc using Mc-Millan's formula.

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eph_ngqpt_fine
Mnemonics: Electron-PHonon : Number of Grid Q-PoinTs in FINE grid.
Executable: abinit
Mentioned in topic: ElPhonInt.
Rarely used: [2/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88],v8:[65]}.
Variable type: integer(3)
Default is [0, 0, 0]

This variable activates the interpolation of the first-order variation of the self-consistent potential in the electron-phonon code. If eph_nqgpt_fine differs from [0, 0, 0], the code will use the Fourier transform to interpolate the DFPT potentials on this fine q-mesh starting from the irreducible set of q-points read from the DDB file. This approach is similar to the one used to interpolate the interatomic force constants in q-space. If eph_ngqpt_fine is not given, the EPH code uses the list of irreducible q-points reported in the DDB file (default behavior).

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eph_transport
Mnemonics: Electron-PHonon: TRANSPORT flag
Executable: abinit
Mentioned in topic: ElPhonInt.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88]}.
Variable type: integer
Default is 0

NB - this does not work yet. This variable can be used to turn on the calculation of transport quantities in the eph module of abinit. Value of 1 corresponds to elastic LOVA as in the PRB by Savrasov and Savrasov

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ph_intmeth
Mnemonics: PHonons: INTegration METHod
Executable: abinit
Mentioned in topic: q-points.
Rarely used: [2/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88],v8:[44]}.
Variable type: integer
Default is 2

Select the integration technique for computing the phonon DOS and the Eliashberg function a2fF(w).

1 for Gaussian scheme (see also ph_smear).
2 for tetrahedron method (no other input is needed but requires at least 4 q-points in the BZ)

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ph_ndivsm
Mnemonics: PHonons: Number of DIVisions for sampling the SMallest segment
Executable: abinit
Mentioned in topic: q-points.
Rarely used: [2/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88],v8:[44]}.
Variable type: integer
Default is 20

This variable is used in conjunction with ph_nqpath and ph_qpath to define the q-path used for phonon band structures and phonon linewidths. It gives the number of points used to sample the smallest segment in the q-path specified by ph_qpath.

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ph_nqpath
Mnemonics: PHonons: Number of Q-points defining the PATH
Executable: abinit
Mentioned in topic: q-points.
Rarely used: [2/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88],v8:[44]}.
Variable type: integer
Default is 0

This integer defines the number of points in the ph_qpath array.

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ph_nqshift
Mnemonics: PHonons: Number of Q-SHIFTs
Executable: abinit
Mentioned in topic: q-points.
Rarely used: [2/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88],v8:[44]}.
Variable type: integer
Default is 1

This variable defines the number of shifts in the q-mesh used for the phonon DOS and for the Eliashberg functions (see ph_ngqpt). If not given, the code assumes a Gamma-centered mesh. The shifts are specified by ph_qshift.

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ph_qshift
Mnemonics: PHonons: Q-SHIFTs for mesh.
Executable: abinit
Mentioned in topic: q-points.
Rarely used: [2/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88],v8:[44]}.
Variable type: real(3,ph_nqshift)
Default is [0, 0, 0]
Only relevant if ph_nqshift

This array gives the shifts to be used to construct the q-mesh for computing the phonon DOS and the Eliashberg functions (see also ph_nqshift. If not given, a Gamma-centered mesh is used.

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ph_smear
Mnemonics: PHonons: SMEARing factor
Executable: abinit
Characteristic: ENERGY
Mentioned in topic: q-points.
Rarely used: [2/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88],v8:[44]}.
Variable type: real
Default is 0.00002 Hartree
Only relevant if ph_intmeth==1

The gaussian broadening used for the integration of the phonon DOS and the Eliashberg function. See also ph_intmeth and ph_ngqpt.

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ph_wstep
Mnemonics: PHonons: frequency(W) STEP.
Executable: abinit
Characteristic: ENERGY
Mentioned in topic: q-points.
Rarely used: [2/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88],v8:[44]}.
Variable type: real
Default is 0.1 meV

The step used to generate the (linear) frequency mesh for the phonon DOS and the Eliashberg function. The extrema of the mesh are automatically computed by the code.

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prtphbands
Mnemonics: PRinT PHonon BANDS
Executable: abinit
Mentioned in topic: printing.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88]}.
Variable type: integer
Default is 1

This option activates the output of the phonon frequencies in the EPH code. Possible values:

- 0 Disable the output of the phonon frequencies.
- 1 Write frequencies in xmgrace format. A file with extension `PHBANDS.agr` is produced. Use `xmgrace file_PHBANDS.agr` to visualize the data
- 2 Write frequencies in gnuplot format. The code produces a `PHBANDS.dat` file with the eigenvalues and a `PHBANDS.gnuplot` script. Use `gnuplot file_PHBANDS.gnuplot` to visualize the phonon band structure.

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prtphdos
Mnemonics: PRinT the PHonon Density Of States
Executable: abinit
Characteristic: DEVELOP
Mentioned in topics: printing, ElPhonInt.
Rarely used: [2/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[89],v8:[65]}.
Variable type: integer
Default is 1

Print the phonon density of states. It is activated by default when optdriver==7.

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prtphsurf
Mnemonics: PRinT PHonon iso-SURFace
Executable: abinit
Mentioned in topics: printing, ElPhonInt.
Rarely used: [1/907] in abinit tests, [0/136] in tuto abinit tests. Test list: {v7:[88]}.
Variable type: integer
Default is 0

Print a bxsf file (Xcrysden format) with the (interpolated) phonon frequencies computed of the q-mesh determined by ph_ngqpt. The file can be use to visualize isosurfaces with Xcrysden or other similar tools supporting the bxsf format. Note that the (dense) q-mesh must be Gamma-centered, shifted meshs are not supported by Xcrysden. This variable requires optdriver==7.

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symdynmat
Mnemonics: SYMmetrize the DYNamical MATrix
Executable: abinit
Mentioned in topic: Phonons.
Rarely used: [0/907] in abinit tests, [0/136] in tuto abinit tests.
Variable type: integer
Default is 1

If symdynmat is equal to 1, the dynamical matrix is symmetrized before the diagonalization (same meaning as the corresponding anaddb variable). Note that symdynmat==1 will automatically enable the symmetrization of the electron-phonon linewidths.

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