Rules of pair electron correlation in MF(M=H, Li, Na)

In this paper, the transferable property of pair correlation energies of F centered orbitals is discussed for a series F containing compounds MF(M=H, Li, Na). Comparing our two calculated results using 6-311++G(d) and cc-PV5Z* basis sets, it is found that the absolute values of the correlation energy of these systems increase with the increase of the size of the basis set, but the following relative changing regularities remain the same. In F containing compounds, from F neutral atom through HF, LiF, NaF to F-, both the intra-, interpair correlation energies and intra-, intershell correlation energies of the inner orbital electrons differ little. The correlation effects of 1s(F)(2) are very much alike in all the above F containing systems and such pair correlation is transferable. However, the valence intrapair correlation and intrashell correlation energies are large and differ a lot in all systems. In MF molecules, the F correlation energy contribution increases with the increase of the ionic bond strength of the compound and this contribution is always between the correlation energy values of F atom and F- anion. For strong ionic compounds, we present a very simple method to estimate the correlation energy of the compound by adding the correlation energies of its component ions and this simple method can reach the chemical accuracy (2 kcal/mol) but require much less computing power. (C) 2001 American Institute of Physics.