[QE-users] Regarding choice of functional for van der Waal corrections

[Sumantra Das]

Dear Quantum Espresso Community,

I am seeking advice on selecting appropriate van der Waals (vdW)
functionals for calculating elastic properties of solids containing F, Cl,
and Br. I'm particularly interested in the accuracy of PBEsol, PBEsol+D2,
and PBEsol+D3.
Concern: PBEsol+D2 and PBEsol+D3 sometimes yield significantly higher
elastic constants (Cijkl) compared to PBEsol alone. In some cases,
PBEsol+D2 values can be four to five times higher, raising concerns about
vdW correction accuracy.

Question: Without experimental elastic constants & lattice parameters, how
can I effectively choose the appropriate vdW correction (D2 or D3) for my
calculations? Is there a recommended approach to identify the most suitable
correction level for a specific system?

Thank you for your time and assistance.

Sincerely
Sumantra Das,
Graduate student
Department of Metallurgical and Materials Engineering,
Indian Institute of Technology Kharagpur
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