ipot ionization

The ION card ionizes all atoms with unique potential index ipot. Negative values and non-integers are permitted, however ionicities larger than 2 and less than $-1$ often yield unphysical results. Our experience with charge transfers using the SCF card suggests values for ionization about 5-10 times smaller than the formal oxidation state. The ION card is probably not needed if the potential is self-consistent. However, it can be used to put some total charge on a cluster. In this case we suggest using the same ionicity for all atoms in the cluster (i.e. total ionization divided by number of atoms). For example, for diatomics like Br2, the fully relaxed configuration has a formal ionization of 1 on the scattering atom. Because of charge transfer, the actual degree of ionization is much smaller. In non-self-consistent calculations the default (non-ionized) scattering potentials are often superior to those empirically ionized, and the results should be checked both ways. If ION is omitted, the atoms are not ionized by default.
  * Simulates effective ionization for formal valence state +1
  * ipot, ionization
  ION  1  0.2