Hello all,
I’m trying to perform structure optimization calculations for vacancy defects in a batch of iron-based alloys and would like to test my workflow on pure BCC-Fe first. I used a 4x4x4 BCC supercell with 128 Fe atoms and removed the middle-most atom to create the vacancy. Only the atom coordinates were allowed to relax. The input file and the pseudopotential (acquired from Pseudo Dojo) are below:
Fe-bulk-v.abi (6.9 KB)
Fe.psp8.txt (273.5 KB)
The problem I am having is that after trying to perform more than twenty steps of relaxation, the maximum atomic force is still the same as it was at the beginning, hovering around 1e-2 Ha/bohr, two orders of magnitude above the convergence criterion I was hoping for, with no signs of decreasing. The results file is below (the job has been manually killed):
Fe-bulk-v.abo (1.3 MB)
I have very little experience with structural optimization of such large supercells and am not sure if this is normal. Also, a single SCF step (not an iteration, just one SCF step) on this supercell takes roughly 6 to 7 CPU hours (more than 2 minutes at ~200 CPU parallelism). Is such a computation time normal?