Electron self-energy in polar material

[tswang]

Dear EPW users,

I have a question about computing electron self-energy in polar materials.

As described in the code, computing the long-range and short-range terms separately may improve convergence. To get the self-energy for each k-point, can I simply sum that from long-range and short-range terms, using the shortrange or longrange tag? Can you talk about how the self-energy from each term is computed in EPW? Thank you!

Best regards.
Tianshi Wang
Graduate student, University of Delaware

[sponce]

Hello Tianshi,

This is something I have coded to test. It should work but there is no test/example available.

In turns out, at least for the case I tested, that it did not really speed up much the convergence with respect to Cauchy Gamma centred random points.

If I remember correctly, you can just sum them.
However, I would advise you to make a small test
1) compute shortrange
2) compute longrange
3) compute all

Verify that long+short gives the same results as all.

Best,

Samuel

[tswang]

Hi Dr. Ponce,

Thank you for your prompt reply. I appreciate it.

You remark in the code that the short-range term still contains a linear long-range part. Does it mean that the short-range term in polar materials has the form as |gS^2+2gLgS| where gS is the matrix elements in non-polar material? Thank you!

Tianshi

[sponce]

Hello,

Yes the short-range part is defined as
g_s = sqrt(g*g - g_l*g_l)

I would need go back to the code to be sure but I think the idea is that you do (g_s+g_l)^2 because you interpolate
the matrix element and not the matrix element square.

[tswang]

Dear Dr. Ponce,

Got you. Thanks a lot!

Tianshi