Hi,
I was wondering how does vasp handle wave function derivative calculations (to generate WAVEDER file) for gamma-only case while using PEAD method? From the wikihttps://www.vasp.at/wiki/index.php/LPEAD, it is based on finite difference between k_j, k_{j+1}, and k_{j-1}. If there is only one k point, how to do the finite difference calculations?
Best,
Xiaoming
Dear Xiaoming Wang,
You can use the LPEAD routines also with the VASP gamma version. For computing the derivatives by the finite difference approach VASP uses the GAMMA point and reciprocal lattice vectors G. This roughly means in the vasp wiki on the LPEAD-site the quantities evaluated at j+1 or j-1 will be evaluated at Gamma+G or Gamma-G. For further information I would recommend you to read the papers by Gonze
https://journals.aps.org/prb/abstract/1 ... .63.155107
and Vanderbilt
https://journals.aps.org/prl/abstract/1 ... .89.117602
All the best Jonathan