# How does density-functional-theory scale with cell size, not with number of electrons

The discussion in How does density functional theory scale with system size? already tells, how DFT scales with the number of electrons. I want to simulate some clusters, so the simulation cell contains much vacuum and its size can be changed without affecting the number of electrons.

I know that with a larger cell less k-points are needed in my plane-wave-code, but I am wondering which further scaling effects there are.

With this in mind, you can use the link you posted to figure out the scaling. In the link, he has four parameters: $n_a$, $n_e$, $n_p$, and $n_v$. $n_v$ is the size of the basis, so when adding vacuum, only the value of $n_v$ will change.