CI method for the study of general molecular potentials

Abstract

A method of configuration interaction designed for general molecular potentials is outlined. The technique employed to arrive at a symmetrized multideterminantal basis for such calculations relies heavily on certain properties of Abelian groups; in particular the ML quantum number commonly employed in atomic structure calculations is replaced in the general molecular case by the index p which labels irreducible representations of some appropriate Abelian group. Formation of the desired symmetrized linear combinations of determinants is thereupon accomplished solely by means of a series of simple diagonalizations, a procedure which insures both the linear independence and the orthonormality of the resultant basis set. CI treatments involving the C4H4 isomer tetrahedrane (Td point group) and the linear nitrous oxide NNO molecule are considered in some detail with a view toward illustrating the use of the techniques described herein. Finally, a survey of a series of recent calculations utilizing the CI method is made and it is concluded from these results that the effects of such treatment vary strongly from one system to another, depending in a very specific manner upon the individual characteristics of a given molecule.