# How to estimate adsorption energy of Li atom on graphene?

I would like to reproduce the data of adsorption energies published in paper.

For example, they say the adsorption energy for Li atom on graphene is -1.19 eV (estimated by GGA-PBE). I used vasp (5.4) code using parameters indicated in the paper and estimated total energy for

Supercell 4x4x1 of graphene: -0.29529545E+03 eV;
Graphene with one Li atom on its surface: -0.29635605E+03 eV;
One Li atom (estimated from bcc structures): -1.909 eV.

Therefore, the adsorption energy should be -296.35605 eV -[(-295.29545 eV) + (-1.909 eV)] = +0.848 eV. It is inconsistent with the previous calculation.

If I use total energy for the isolated Li atom of -0.29471258 eV, the obtained adsorption energy is -0.767 eV. Both have a big gap with the published data. I wonder if there is a trick to accurately estimate the adsorption energy?

• Hi, I edited your title to make it more clear. Feel free to roll back or re-edit if it doesn't fit what you are asking. Jun 20, 2021 at 12:34
• Does your optimized geometry match the literature one? Jun 20, 2021 at 12:58
• @wzkchem5, I am sorry it is not matched. The result above is on top of C. At the hollow site, it should be -1.104 eV using the total energy of the isolated Li atom. But I don't know when I should use the total energy of one Li atom estimated from bcc structures? And when I should use the total energy of an isolated Li atom? Jun 21, 2021 at 1:40
• Adsorption energies of atoms are defined with respect to isolated atoms, unless otherwise specified. I think you should first try to reproduce the literature geometry. If the geometry is wrong, you can never get the energy right. Jun 21, 2021 at 9:38
• @NikeDattani OK, I'll do that Jun 29, 2021 at 12:55