Rules on pair electron correlation in MOH (M = H, Li, Na)

In this article, the transferable property of pair correlation energies of OH components is discussed for a series of OH containing compounds MOH (M = H, Li, Na). In this series of compounds, from OH free radicals through HOH , LiOH, NaOH to OH-, both the intra- and interpair correlation energies and intra- and intershell correlation energies of the inner orbital electrons change little. The 1s(O)(2) is very much alike in all the above OH containi ng systems and such a pair correlation is transferable. But the interpair c orrelation and intrashell correlation energies of the valence electrons are large and change a lot in all systems. In MOH molecules, the OH correlatio n energy contribution increases with the increase of the ionic bond strengt h of the compound and this contribution is always between the correlation e nergy values of OH free radicals and OH- atomic groups. For strong ionic co mpounds, we present a very simple method to estimate the correlation energy by adding the correlation energies of its component ions within the chemic al accuracy (2 kcal/mol). (C) 2001 John Wiley & Sons, Inc.