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Why would you want to generate a pseudopotential for a cation/anion? The pseudopotential is only for the inner core electrons. The only case where you'd want to do this is when the charge state of the …

You are making an approximation by including the semicore states in the pseudopotential. Like the name suggests, semicore states aren't really core states; they lie higher up in energy so they may not …

You should not be thinking about a specific perturbation operator. The key thing here is that the orbitals are Kohn-Sham eigenfunctions, and that already reveals everything that is needed. Still, it t …

To add to Nike's list, one should also differentiate between the energy consistent pseudopotentials used in quantum chemistry and the shape consistent pseudopotentials that dominate in the solid state … Energy consistent pseudopotentials are also shape consistent, while shape consistent pseudopotentials result in much larger errors in the energy than with the energy consistent potentials. …

Velocity is not really used in quantum mechanics, since it is the momentum that is the canonical variable. Leave velocity to classical physics. The momentum operator ${\bf p}$ makes sense for whateve …

This is the hybrid Gaussian and plane wave method described in Mol. Phys. 92, 477 (1997), in which you expand the orbitals $\psi_{i\sigma}$ in a Gaussian basis set, but compute the Coulomb interaction …

Shape consistent pseudopotentials are just commonly used for some reason, even though energy consistent pseudopotentials are "the right way to do it". … The reason why shape consistent pseudopotentials keep on being used is that the errors in the density functional approximations themselves are so large that the extra error from the pseudopotentials can …