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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 k-point grid (or a scf calculation
followed by a non-scf one on the dense k-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 k and k+q grid points used in the subsequent electron-phonon
calculation. All grids MUST be unshifted, i.e. include k = 0.
- a normal scf + phonon dispersion calculation on the coarse k-point
grid, specifying option elph=.true.. 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 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 PH/lambda.f90)
to get the
F(
) function, the electron-phonon coefficient
, and an estimate of the critical temperature Tc.
For more details, see Example 07.
Next: 7.4 Distributed Phonon calculations
Up: 7 Phonon calculations
Previous: 7.2 Calculation of interatomic
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Build Daemon user
2012-05-24