# Divergence behaviour of surface energy

By definition, the surface energy of a thin film or a slab model is defined as

$$\sigma = \frac{1}{2A}(E_{slab} - N\cdot E_{bulk})$$

where $$N$$ is the number of atoms in the thin film and $$E_{bulk}$$ corresponds to the average energy of the atom in its bulk phase. I should expect that the surface energy of the slab converge to certain value when I keep increasing the number of layers but what I found is the surface energy of my system increases linearly. I think this is unreasonable. Is there anyone who met this problem before?

• Kindly share more data like POSCAR, INCAR, KPOINT. Mar 26 at 16:57
• What are $E_{slab}$ and $\sigma$ ? Mar 29 at 10:53