Application of many‐body perturbation theory in the localized representation for the all‐trans conjugated polyenes

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Abstract
Ab initio self‐consistent field (SCF) calculations are performed with the standard 6‐31G* basis set for all‐trans conjugated oligomers C2n+2H2n+4. The canonical occupied and virtual molecular orbitals (MOs) are separately localized by unitary transformations. Due to the localization, the perturbation operator is partitioned into two‐particle and into single‐particle terms; the MBPT is, therefore, a double‐perturbation expansion in this case. By using the localized representation of the MBPT, the correlation energy contributions can be partitioned into local and nonlocal effects. It can be shown that the local effects are very important and well transferable, which makes possible the calculation of the correlation energy of larger molecules if the localized molecular orbitals (occupied and virtual) of smaller related molecules are known. © 1994 John Wiley & Sons, Inc.