Title of article :
Molecular orbital models of benzene, biphenyl and the oligophenylenes Original Research Article
Author/Authors :
Robert J. Bursill، نويسنده , , William Barford، نويسنده , , Helen Daly، نويسنده ,
Issue Information :
هفته نامه با شماره پیاپی سال 1999
Abstract :
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 π-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.
Journal title :
Chemical Physics
Journal title :
Chemical Physics