Understanding the impact of correlation on bond length alternation in polyenes

This article analyzes the electronic factors governing bond length alternation (BLA) in linear polyenes. The impact of various effects is illustrated on small all-trans polyenes, namely butadiene, hexatriene and octatetraene prototype molecules. It well known that self-consistent-field single determinant treatments overestimate paper aims to identify physical correlation which correct this defect. question addressed using an orthogonal valence bond-type formalism wave function expressed terms strongly localized bonding antibonding molecular orbitals. shows dynamic polarization π orbitals accounted for full-π complete active space significantly reduce alternation. These are brought by excitations applied inter-bond charge transfer determinants. σ bonds, either CC or CH character, analyzed afterward enlarging adding 1hole-1particle excitations. shown these also decrease BLA increase coefficients Moreover, relation with ligand-to-metal metal-to-ligand (LMCT MLCT, respectively) components magnetic transition-metal compounds discussed.