Example calculation in a polar material with long-range e-ph interactions.

Run the calculations in the directory “pw-ph-wann” 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 (“example02-silicon-perturbo”, 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 non-polar part), or just the polar or nonpolar part.

  • For the long-range (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 short-range (nonpolar) part, we use rmpolar for the variable polar_split and 'uniform' for sampling.

Remember to converge both the long- and short-range parts of the e-ph matrix elements with respect to the number of \(\mathbf{q}\) points (the variable nsamples). If polar_split is not specified, perturbo.x will compute e-ph matrix elements including both the short- and long-range interactions, which typically has a slow convergence with respect to number of \(\mathbf{q}\) points.