Accuracy Diag in metals

Ex. 1 5 atoms 50 electrons: 5 layers of Ni 5 vacuum in (100)

On the Y-axis, we plot the difference between the energy at each SCF cycle and the final energy ofr accuracy_diag of 1e-12. The same final energy is achieved for 1e-10 as for 1-12, and 1e-10 is a little bit faster. For decreasing settings we do see a speedup, but at a cost of accuracy. 1e-8 is probably still accurate enough, but to be sure one would have to look at the forces.