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Charge and spin correlation structures of conjugated π systems: Analysis of full CI wave functions of the PPP hamiltonian
Author(s) -
Hashimoto Katsufumi
Publication year - 1982
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560210512
Subject(s) - ground state , excited state , wave function , hamiltonian (control theory) , spins , chemistry , singlet state , atomic physics , electronic correlation , antiferromagnetism , physics , condensed matter physics , molecular physics , electron , quantum mechanics , mathematical optimization , mathematics
An analysis of the electronic correlation structures by means of the charge and spin correlation functions is carried out for full CI wave functions of four, five, and six membered conjugated π systems described by the Pariser–Parr–Pople Hamiltonian. The low‐lying states of these systems are classified as covalent ( CV ) and ionic ( IN ) states depending on whether the probability of finding two electrons simultaneously at the same position is small or large. It is found that many of excited CV states, the typical ones of which are the 2 1 A g state of linear π systems, have stronger CV character than the ground CV state, and their spin coupling structures are different from each other as well as from that of the ground CV state. The spin coupling structure in the ground CV state has an “antiferromagnetic” spin arrangement in favor of antiparallel coupling between nearest neighbor spins while in excited CV states the extent of the antiparallel spin coupling between nearest neighbor sites is decreased. IN states, which are less common for low‐lying states than CV ones, are also found to have characteristic modulations in the charge correlation. In particular, the charge correlations in the lowest singlet IN states, 1 1 B u of linear π systems, 1 1 B 2g of cyclobutadiene and 1 1 B 1U of benzene, are alternating.