In the phonopy processing, we obtain force constants by running phonopy
If someone ask:
What was the q-grid used to compute the force constants?
My reply is:
In the VASP-DFPT lattice dynamics calculation of a crystal made of *l*x*m*x
*n* periodic cells, the q-point grid to compute the interatomic force
constants is also *l*x*m*x*n*. This means, if I had done the lattice
dynamics calculation with the 1x1x1 primitive unit cell, the q-points grid
for force constants is also 1x1x1. If the calculations were done with
2x2x2 supercell, the q-points grid for IFCs is also 2x2x2.
(This further means that VASP-DFPT requires supercell for accurate IFCs).
Please verify these.
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