Changing Rules of Bonding Electron Pair Correlation Energies of CH3X （X = F, OH, NH2） Systems

1 INTRODUCTION It has been known that the electron correlation energy of molecular systems was, and still is, one of the most serious bottleneck problems to the chemis- try accuracy of computational quantum chemistry. Since L鰓din1] gave the definition …

Changing Rules of Bonding Electron Pair Correlation Energies of CH3X (X = F,OH,NH2) Systems

The pair correlation energy of bonding electrons is used and analyzed in the cal-culation of C-H and C-Y (Y = F, O, N) bonding electron pairs in CH3X (X = F, OH, NH2) isoelec-tronic systems based on intra- and interpair correlation energy results at both MP2-OPT2/6-31 l G(d) and MP2-OPT2/cc-pVtz levels with MELD program. Comparison of two set resultsshows that cc-pVtz and 6-311 G(d) give more correlation energy of valence electrons andinnermost core electron pairs, respectively in these systems, resulting that the total correlationenergy with cc-pVtz basis of each system is larger than that with 6-311 G(d). Investigations ofpair correlation energy show that with the decrease of electronegativity of X atom and the increaseof H atoms in these CH3X (X = F, OH, NH2) systems, the pair correlation energy of lsc^2 of the Catoms is transferable, and the correlation energy of C-H bonding electron pair with little changes isof approximate transferability, while those of C-Y (C-F, C-O, C-N) bonding electron pair decreasein a large extent from CH3F through CH3OH to CH3NH2 molecules. It is suggested that the study ofpair correlation energy of bonding electrons will further deepen the understanding of electron corre-lation effect from traditional chemical bonding concept.