Preoptimised VB: a fast method for the ground and excited states of ionic clusters II. Delocalised preoptimisation for He2+, Ar2+, He3+ and Ar3+ Original Research Article

We generalise the preoptimisation of orbitals within VB (Part I of this series) through letting the orbitals delocalise on the neighbouring fragments. The method is more accurate than the local preoptimisation. The method is tested on the rare gas clusters He2+, Ar2+, He3+ and Ar3+. The results are in good agreement with previously published data on these systems. We complete these data with higher excited states. The binding energies of (ArCO)+, (ArN2)+ and N4+ are revisited. The simulation of the SCF method is extended to Cu+H2O.