Molecular orbital models of benzene, biphenyl and the oligophenylenes

被引:6
作者
Bursill, RJ [1 ]
Barford, W
Daly, H
机构
[1] Univ New S Wales, Sch Phys, Sydney, NSW 2052, Australia
[2] Univ Sheffield, Dept Phys, Sheffield S3 7RH, S Yorkshire, England
基金
澳大利亚研究理事会; 英国工程与自然科学研究理事会;
关键词
D O I
10.1016/S0301-0104(99)00017-8
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
A two-state (2-MO) model for the low-lying long axis-polarised excitations of poly(p-phenylene) oligomers and polymers is developed. First we derive such a model from the underlying Pariser-Parr-Pople (P-P-P) model of pi-conjugated systems. The two states retained per unit cell are the Wannier functions associated with the valence and conduction bands. By a comparison of the predictions of this model to a four-state model (which includes the non-bonding states) and a full P-P-P model calculation on benzene and biphenyl, it is shown quantitatively how the 2-MO model fails to predict the correct excitation energies. The 2-MO model is then solved for oligophenylenes of up to 15 repeat units using the density matrix renormalisation group (DMRG) method. It is shown that the predicted lowest-lying dipole-allowed excitation is ca. 1 eV higher than the experimental result. The failure of the 2-MO model is a consequence of the fact that the original HOMO and LUMO single particle basis does not provide an adequate representation for the many-body processes of the electronic system. (C) 1999 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:35 / 44
页数:10
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