Example calculation in a polar material with longrange eph interactions.
Run the calculations in the directory “pwphwann” to obtain the data needed to run qe2pert.x
. Run qe2pert.x
to get ‘prefix’_epwan.h5, which is required for all calculations using perturbo.x
.
The input file for each calculation using perturbo.x
is similiar to the silicon case (“example02siliconperturbo”, link). The main difference is the 'imsigma'
calculation, where users can use a variable called polar_split to specify whether they want to compute the full matrix element (polar plus nonpolar part), or just the polar or nonpolar part.

For the longrange (polar) part, we set
polar_split='polar'
in the input file. In this example, we use'cauchy'
for \(\mathbf{q}\) point importance sampling and set the variable cauchy_scale for the Cauchy distribution. 
For the shortrange (nonpolar) part, we use
rmpolar
for the variable polar_split and'uniform'
for sampling.
Remember to converge both the long and shortrange parts of the eph matrix elements with respect to the number of \(\mathbf{q}\) points (the variable nsamples). If polar_split is not specified, perturbo.x
will compute eph matrix elements including both the short and longrange interactions, which typically has a slow convergence with respect to number of \(\mathbf{q}\) points.