Hello expert,
I noticed that in the Optic section, there are calculations related to frequency-dependent nonlinear optical dielectric functions and second-order nonlinear optical polarizability. In the Static Nonlinear Properties section of the DFPT module, there are also calculations for dielectric constants, SHG, and electro-optic coefficients. The former can use scissors correction for the band structure, but why is there no scissors correction in the latter?
Hello,
The formalism used is quite different. In the optic case it’s a sum over states where you can correct the band gap before the sum (making sure you also renormalize the momentum matrix elements.).
In the dfpt case, you solve the sternheimer equation, which relies on relations between the psi0 and psi1, including the eigenvalues. If you were to change it during the scf cycle I’m not sure what would happen. Once you have all of the dfpt quantities, you might renormalize or combine them with a band gap scissor correction. You might check the literature to see if this has been used successfully.
Best
Matthieu