elastic constants using vaspkit

[mohamed_daoud]

Hi,

I am using vaspkit to genrate INCAR for elastic constants calculation using strain-energy method. I keep getting wrong values for the elastic constants for some structure, despite the fact that I keep ISIF=2, IBRION =-1 and resonable KPINTS mesh. Is there some tags I should consider or change, maybe the ionic relaxation I did was wrong?. Your response and help will be much appreciated

[fabien_tran1]

Hi,

This is difficult to provide help without more information. For instance, you should provide details about the procedure that you followed; does it correspond to what is described at https://vaspkit.com/tutorials.html#dete ... ain-method?

Actually, note that at the IBRION and Phonons_from_finite_differences pages, it is mentioned that the elastic and internal strain tensors are calculated if ISIF \(\ge 3\).

The results may also depend significantly on various parameters like for instance the size of the basis set (ENCUT) or the convergence criterion (EDIFF). Did you check the convergence of the results with respect to such parameters?

[mohamed_daoud]

Hi,

Thank you for your response. I followed exactly the procedure in vaspkit tutorials for simple Al unit cell but I got Close values for elastic constant to literature( ISIF=2, IBRON=-1, ENCUT =520 eV, and KPOINTS= 21×21×21, EDIFF= -1.6E-6). I tried the same procedure with same paramter for different unit cell structures like Al3Sc and Al3Sm and I got wrong values for th elastic constants. I checked the convergence for these calculations and it was OK. Your help will be greatly appreciated it