My Community

Dear VASPers,

I have a question about the reference energy in VASP (I know that this issue has been discussed in this board, but I am not completely clear about how the reference energy is defined).

I need to compare the energies of VBM between two similar systems. One has a geometrical distortion with an additional atomic species. For example, one has C only and the other has C and H. I want to see how the distortion shifts VBM.

Since the Kohn-Sham eigenvalues are calculated with respect to a certain reference energy, I believe that I can't make direct comparison between the two VBM energies because the reference energies are different.

I would greatly appreciate if anyone lets me know how to make a right comparison between Kohn-Sham eigenvalues in two different systems. In other words, how can I align the reference energies in the two systems so that I have the same energy zero line?

Thank you all.

You would have to take the vacuum energy as zero. Search for vtotav in that forum. It works for slabs only.

Hth, alex

Thanks, Alex.

The problem is: my system is bulk.