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Since v.5.0, there are two ways of calculating electron-phonon
coefficients, distinguished according to the value of variable 
electron_phonon. The following holds for the case 
electron_phonon= 'interpolated' (see also Example 03).
The calculation of electron-phonon coefficients in metals is made difficult 
by the slow convergence of the sum at the Fermi energy. It is convenient to 
use a coarse k-point grid to calculate phonons on a suitable 
wavevector grid;
a dense k-point grid to calculate the sum at the Fermi energy. 
The calculation
proceeds in this way:
- a scf calculation for the dense  -point grid (or a scf calculation 
followed by a non-scf one on the dense -point grid (or a scf calculation 
followed by a non-scf one on the dense -point grid); specify 
option la2f=.true. to pw.x in order to save a file with 
the eigenvalues on the dense k-point grid. The latter MUST contain 
all -point grid); specify 
option la2f=.true. to pw.x in order to save a file with 
the eigenvalues on the dense k-point grid. The latter MUST contain 
all and and + + grid points used in the subsequent 
electron-phonon 
calculation. All grids MUST be unshifted, i.e. include grid points used in the subsequent 
electron-phonon 
calculation. All grids MUST be unshifted, i.e. include = 0
. = 0
.
- a normal scf + phonon dispersion calculation on the coarse k-point
grid, specifying option electron_phonon='interpolated', and 
the file name where
the self-consistent first-order variation of the potential is to be 
stored: variable fildvscf).
The electron-phonon coefficients are calculated using several
values of Gaussian broadening (see PHonon/PH/elphon.f90) 
because this quickly
shows whether results are converged or not with respect to the 
k-point grid and Gaussian broadening.
- Finally, you can use matdyn.x and lambda.x 
(input documentation in the header of PHonon/PH/lambda.f90)
to get the 
 F( F( )
 function, the electron-phonon coefficient )
 function, the electron-phonon coefficient , and an estimate of the critical temperature Tc
. , and an estimate of the critical temperature Tc
.
See the appendix for the relevant formulae.
Important notice: the 
q  0
 limit of the contribution 
to the electron-phonon coefficient diverges for optical modes! please 
be very careful, consult the relevant literature. .
 0
 limit of the contribution 
to the electron-phonon coefficient diverges for optical modes! please 
be very careful, consult the relevant literature. . 
 
 
 
 
 
 
 
  
 Next: 5 Parallelism
 Up: 4 Using PHonon
 Previous: 4.2 Calculation of interatomic
     Contents 
Layla Martin-Samos Colomer
2012-11-21