I am having problems converging an ionic, extended system. What can I do?
This problem usually shows up when a minimum basis set is used and where a lot of charge has to be moved a long way but the minimal basis does not provide a lot of coupling between the orbitals. The initial guess may be modified by • putting the charge on the atoms where it is believed to be, • look at the orbitals and swap the orbitals to obtain the correct occupation, or • use the fragment guess. Better yet, use a better basis set which will allow for better coupling of the orbitals!
