Hello!
I am studying the adsorption energy of an organic semiconductor molecule (pentacene) on a metal (copper) surface and I have a few questions about ENCUT and k-point convergence.
I had previously done these convergences just for the unit Cu cell and was converging based on the E0 value. After reading further, I have learned that it is beneficial to converge based on the adsorption energy, because that is my property of interest. This means that I will need to collect the value of (E0 - KE correction term) for the surface on its own, then for the molecule on its own, then for the combined system.
1) I have read that when modelling a single molecule, you should always use just the Gamma point for your k-point mesh. I would assume, however, that you should use the same k-point mesh for all three sets of runs (surface, molecule, combined) of the process. Is this true? If that's the case, will you end up using a non-gamma point mesh for the molecule?
2) When I previously did k-point convergence for just the Cu unit cell, the intended process was: 1) Converge k-points for single unit cell 2) Do Cu layer convergence. Every time the size of the Cu cell doubles in the z direction, halve the number of k-points in the z direction. 4) Do vacuum convergence on the pentacene molecule to determine how far apart the molecules would need to be to avoid interaction. Make the Cu cell this size in the x and y directions, similarly decreasing the number of k-points as the cell increases in size. Should I instead not do any of this halving and just converge the k-points for my adsorbed system and use that value?
If it is easier for you to just explain the process of ENCUT and k-point convergence for an adsorbed system step by step instead of directly answering my questions, that is fine!
Thanks!
Emily