henniggroup / VASPsol

Solvation model for the plane wave DFT code VASP.
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FERMI_SHIFT calculation in VASPSol #58

Closed MSJavaScript closed 3 years ago

MSJavaScript commented 3 years ago

In solvation.F, fermi_shift is calculated by VACPOT_POIS - VACPOT_PSP. Both VACPOT_POIS and VACPOT_PSP are some electrostatic potential where the electron density reaches a minimum. VACPOT_PSP is calculated from Hartree potential and ionic potential (with the local part of ionic pseudopotential) from POTLOK subroutine in pot.F, while VACPOT_POIS is calculated from the Hatree potential generated by total charge density (electron density plus ionic gaussian density, without local pseudo potential).
So it seems that VACPOT_POIS is a potential reference. Can anyone tell me why ? Thanks.

ericfonseca95 commented 3 years ago

Hello, This potential shift is needed to align VASP's internal potential reference of 0 to the Poisson equation's reference potential. The Poisson equations natural reference is the bulk electrostatic potential in the electrolyte.

See the paper for more details: Mathew, K., Kolluru, V. S. C., Mula, S., Steinmann, S. N., & Hennig, R. G. (2019). Implicit self-consistent electrolyte model in plane-wave density-functional theory. Journal of Chemical Physics, 151(23), 1–8. https://doi.org/10.1063/1.5132354

Eric Fonseca