![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
Abstract
Pariser-Parr-Pople, Hubbard, and Heisenberg models for systems with one electron per site, such as the π-networks of neutral conjugated hydrocarbons, are considered. It is argued that for usual systems the Hubbard model describes reasonably only those states that are also capable of being so described by a Heisenberg model. Such Heisenberg models are given by a cluster expansion, surpassing in accuracy the results of correspondingly low-order degenerate perturbation expansions.
Research supported by the Robert A. Welch Foundation of Houston, Texas, U.S.A.
Research supported by the Robert A. Welch Foundation of Houston, Texas, U.S.A.
Notes
Research supported by the Robert A. Welch Foundation of Houston, Texas, U.S.A.