I tried to add vacuum to the bulk with two ways but for some reason I’m getting different energies in each case (for the same geometry) :
Case 0. took bulk, 0 4 0 4 0 4 and the same size of simulation box.
Case 1. created simulation box, 0 4 0 4 -1 5. And created atoms on the smaller region, so that the vacuum was left in +z and -z directions, i.e. create_atoms 0 4 0 4 0 4.
In this case more atoms were created than in bulk case in the same region, and energy also differed from that of bulk. I don’t understand why number of atoms increased. It’s not even the same if I filled the entire box.
Case 2. created bulk 0 4 0 4 0 4 and the simulation box of the same size, then tried to change box using change_box command without remapping atoms:
change_box all z final -1 5
Here again, I got different value for energy than that from bulk, but the number of atoms remained the same.
In summary, I get:
#bulk(pbc, no vacuum): N=256, E=-74.554717/atom
#case 1: N=288, E=-73.342496/atom
#case 2: N=256, E=-73.190968/atom
I would explain energy differences from bulk value with surface effect but I haven’t relaxed the system, just set up geometries. And why the two per atom energies in Case1 and Case2 differ?
Third option could be filling the box and deleting atoms so that the vacuum is left. I have bulk and just want to add vacuum without disturbance. I’m confused which way is the correct one since I get different energies for any option.
Thanks for any suggestion. Files attached.
ffield.reax.Al (21.7 KB)
in.vactest (739 Bytes)
al_control (511 Bytes)