Localization of a combinatorial procedure for singly occupied fragment FMOs

In order to ensure that each of all opened shell-fragment MOs (FMO Phi (i)) , obtained from the UHF computation for a molecular fragment, has a correct electronic occupancy, the FMOs Pi have to be localized. However, the speci fied symmetrization of the singly occupied FMOs (Phi (s)) is destroyed whil e Phi (s) becomes singly occupied after the Kost localization. The Perkin l ocalization, a computational procedure after the Kost localization, transfo rms Phi (s) into phi (s) which possesses now the symmetrization which they should have. The way of the Kost localization and setting of the length of the bond C-HR between the carbon atom and its referential hydrogen atom H-R have great effects on the symmetric characters of the localized FMOs obtai ned from the Perkin localzation. In the case of the Gaussian basis sets suc h as STO-3G, 3-21G and 4-31G, the bond length r should be set to 0.1 nm, an d when 6-31G is used, it should be 0.09 nm.