Dear researchers
I want to know what type of Pseudopotential is appropriate for calculating atomic force constants for fcc structures by quantum espresso?
Thanks
Giang Nguyen Recently I opted PAW pseudopotential for the first time for my material. Till then, I was doing the same with ultrasoft pseudopotential. I observed that time taken for computation of energy by scf calculation and phonon calculation was more when I used PAW. Almost double. Also the number of iterations for energy convergence in scf calculation were more compared to ultrasoft. May I know why is it so?
Giang Nguyen I'm working on CaO. Any specific reason for PAW taking more time?
Giang Nguyen that isn't actually correct, ultrasoft pseudopotentials are not norm-conserving. In fact the ultrasoft and PAW methods are formally almost identical, it is largely a matter of whether the projectors are considered part of the wavefunction, or part of the pseudopotential. There are some differences (ultrasofts also pseudise the augmentation charge, for example) but they have never been shown to make any meaningful difference in simulations.
The computational cost of a method also depends on the number of projectors in the pseudopotential, as well as the cut-off energy for the wavefunctions (and density cut-off). If the PAW potential has more projectors, that would make it slower.
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