Molecular orbital-configuration interaction

As with benzene we study only the tt system using the SEP to account for the presence of the a orbitals. It is not the purpose of this book to compare MCVB with molecular orbital configuration interaction (MOCI) results, but we do it in this case. 

Improvement of the MO method involves better orbitals, better account of interelectronic repulsion, and introduction of mixing of different electron configurations in the molecular orbitals ( configuration interaction ). Improved MO calculations give much more accurate energies at the minimum of a plot such as Figure 21-11, but the bonds still do not dissociate properly, for the same reason as with the simple MO method. 

Mapping Molecular Orbital—Configuration Interaction to Valence Bond Wave Functions... 

MAPPING A MOLECULAR ORBITAL CONFIGURATION INTERACTION WAVE FUNCTION INTO A VALENCE BOND WAVE FUNCTION... 

Projecting the Molecular Orbital Configuration Interaction Wave Function Onto the Rumer Basis of Valence Bond Structures... 

Spin Polarization of Molecular Orbitals [Configuration Interaction)... 

Hence the approximation (1), which is a prototype of multistructure valence bond theory, is equivalent to approximation (4), a prototype of molecular orbital configuration interaction theory, and both (1) and (4) are equivalent to (13), the Coulson-Fischer wave function. 

TABLE 7.4 MOLECULAR ORBITAL CONFIGURATIONS AND OTHER DATA ABOUT PERIOD 2 ELEMENTS. IT IS UNDERSTOOD THAT EACH MOLECULE HAS A COMPLETE S1s AND s is ORBITAL. NOTE THAT OXYGEN, FLUORINE, AND NEON HAVE A SLIGHTLY DIFFERENT ORDER DUE TO INTERACTIONS BETWEEN 2s AND 2p ORBITALS. 

PNO-CI (Pair Natural Orbital Configuration Interaction) and CEPA-PNO (Coupled Electron Pair Approximation with Pair Natural Orbitals) Calculations of Molecular Systems. I. Outline of the Method for Closed-Shell States. 

Mulliken and Coulson hoth agreed that configuration interaction may become very important in the more comphcated molecules when one starts with molecular orbital configurations. "Of course, this is all very famihar, but I think it is interesting to see how configuration interaction becomes important in different places in the AO and the MO methods." (CP, Ms. Coulson 154, Box G.15, G.15.5. Letter Mulltken to Coulson, January 24, 1949.)... 

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