Dielectric function beyond IPA

[atul_pandey]

Dear Sir,

Which tag should be used instead of LOPTICS = .TRUE. for the calculation of frequency-dependent dielectric function for semiconductor and metallic materials using GW or hybrid functional? There is mention to use this tag for insulator only. I have attached the screenshot below.

[martin.schlipf]

For GW, you do not need to set the LOPTICS tag to get the dielectric function. I would recommend against using hybrid functionals for metals because their Hartree-Fock contribution tends to open a gap.

If you find that LOPTICS does not work, we have a couple of other methods that you can use to compute dielectric properties.