Degenerate bands in EPW calculations

[hanghuichen]

Dear EPW developers,
The reference PRB 87, 024505 (2013) says that in the implementation of EPW, the el-ph self-energy is assumed to be diagonal in band indices. Does this approximation break down for systems with multiple-degenerate bands at the Fermi level?
For example, a simple cubic perovskite oxide ABO3, upon electron doping, the Fermi level crosses three degenerate t2g bands of the B ion. In that case, can we still assume that the el-ph self-energy is diagonal in band indices and off-diagonal terms are neglected?
Thank you very much.

Dr. Hanghui Chen
Department of Physics
NYU Shanghai and New York University