[Pw_forum] Documentation for fd_ef.x

Andrew Supka supka1ar at cmich.edu
Mon Feb 26 00:32:05 CET 2018

Lorenzo is correct in that it's reasonably expensive to do it with fd_ef.x.

I'm attaching two files:

1.) fd_ef.x input
2.) An scf file for one of the polarization directions needed.

The seven directions and their order are mentioned in the fd_ef.x input

Depending on the symmetry of your system you can reduce the number of
polarization directions you need to actually calculate.

You will have to run the scf calculations for each polarization direction
and copy from each output the converged values (the last one) for the
electronic dipole:

Electronic Dipole on Cartesian axes
           1 -3.224342350515147E-003
           2 3.224063842650654E-003
           3 0.889627066087568

Into the fd_ef.x input.

Keep in mind that the example scf input is just an example and you should
test the scf input parameters (particularly the kp grid) to verify they're
adequate for your system.

Good luck!

Andrew Supka
PhD Student
Central Michigan University

On Feb 25, 2018 5:33 PM, "Lorenzo Paulatto" <paulatz at gmail.com> wrote:

On 02/25/2018 07:58 PM, Robert Wexler wrote:
> force constants. Since ph.x, to the best of my knowledge, cannot handle
> vdW corrections,
 > ... QE version 5.1.

The current version ph.x can handle vdW corrections with no problems,
but you'll have to upgrade, because v5.1 is very old.

To get epsilon doing finite derivatives from modern theory of
polarization, via fd_ef, or not by hand, the only difficulty are the
units of measure, is not very efficient it would probably take a billion
k-points. If you insist, and manage to do it, please send us a working


Lorenzo Paulatto - Paris
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Pw_forum at pwscf.org
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