Increasing the supercell size gives atoms more freedom to relax. I think one needs to consider different supercells to see how the elastic constant converges against the system size.

Thank you Manh-Thuong Nguyen for your valuable reply.

One thing I want to ask here is that after the calculations, I might get higher values. Then to obtain the correct values of elastic constants I need to reduce them? and how can I do that?

Manh-Thuong Nguyen

sorry if i mind you. I got a VASP work for calculation of change in energy of Bi2O3 with nitrogen ( nitrogen reduction reaction). I do not know when my geometric slab is optimization. i mean i set a EDIFFG = -0.01 for my INCAR and it works ! Does that means my structure is optimized. i attached some my result

Your log file ends with an error, so I suspect that the adjustment of the ionic positions after the first step lead to a configuration where some ions are too close or something similar happened. Check the contcar after the first calculation and compare to the initial poscar.

If you do a spin-polarized calculation, it may also be better to initialize with magnetic moments (MAGMOM parameter)

Payal - I think one way is that you systematically increase the size of the supercell and calculate the elastic constant. At some point, the elastic constant doesn't really change against the supercell size, you can use that value.

Nhut Nguyen - I don't use VASP. In general, one can check if a structure is optimized (to a local minimum) by considering the forces (if small enough) and the vibrational frequencies (if no imaginary vibrational modes). And also, as Martin pointed out, for magnetic systems, proper initial magnetic moments are also important as it helps obtain ground states.

Nhut Nguyen

If you want to know if your GO worked, check for the following phrase at the end of your OUTCAR file:

reached required accuracy - stopping structural energy minimisation

Also to know the number of iterations done for you calculation to converge, run the command:

grep entropy= OUTCAR | wc -l

Dear all,

I am here to know that how to calculate Elastic constant using VASP ? I did calculation using BRION=6 and ISIF>=3 and what will be the next step ?