How to handle the long-range interaction in electron-phonon coupling (EPC) within the EPW code
Posted: Mon Sep 01, 2025 2:42 am
Dear developer,
I would like to understand how to handle the long-range interaction in electron-phonon coupling (EPC) within the EPW code. From the EPW website and the paper titled "Electron–phonon physics from first principles using the EPW code", I understand that EPW first subtracts the long-range interaction and then reintroduces it by setting appropriate input tags. However, I am unsure how to configure these tags correctly.
1. If I only set lpolar = .true., which interactions are included in the EPC? I assume that the EPC would match the DFPT result (including all interactions) when only lpolar = .true. is set, with all other tags kept at their default values.
2. The vme and system_2d tags seem to control the type of long-range interaction considered. If I set system_2d = 'dipole_sp', does that include both dipole-dipole and short-range interactions? Similarly, if I set system_2d = 'quadrupole', are dipole, quadrupole, and short-range interactions all taken into account?
3. For a bulk system, if I set system_2d = 'no', does that account for the long-range interaction (dipole plus quadrupole) in 3D? If the quadrupole.fmt file is not provided, is only the dipole interaction considered for the bulk system?
4. If longrange = .true. is set, only the long-range interaction is included while the short-range part is subtracted. What happens if shortrange = .true. and longrange = .false.? Does that include both short-range and long-range contributions?
Thank you.
I would like to understand how to handle the long-range interaction in electron-phonon coupling (EPC) within the EPW code. From the EPW website and the paper titled "Electron–phonon physics from first principles using the EPW code", I understand that EPW first subtracts the long-range interaction and then reintroduces it by setting appropriate input tags. However, I am unsure how to configure these tags correctly.
1. If I only set lpolar = .true., which interactions are included in the EPC? I assume that the EPC would match the DFPT result (including all interactions) when only lpolar = .true. is set, with all other tags kept at their default values.
2. The vme and system_2d tags seem to control the type of long-range interaction considered. If I set system_2d = 'dipole_sp', does that include both dipole-dipole and short-range interactions? Similarly, if I set system_2d = 'quadrupole', are dipole, quadrupole, and short-range interactions all taken into account?
3. For a bulk system, if I set system_2d = 'no', does that account for the long-range interaction (dipole plus quadrupole) in 3D? If the quadrupole.fmt file is not provided, is only the dipole interaction considered for the bulk system?
4. If longrange = .true. is set, only the long-range interaction is included while the short-range part is subtracted. What happens if shortrange = .true. and longrange = .false.? Does that include both short-range and long-range contributions?
Thank you.