OPTIMAL PARAMETRIZATION OF THE PARISER-PARR-POPLE MODEL FOR BENZENE AND BIPHENYL

We obtain a parametrisation of the Pariser-Parr-Pople model of the rr- conjugated systems which is optimal for benzene, biphenyl and poly( pa ra-phenylene). We first optimise agreement with experiment for a numbe r of low-lying excitations of benzene, leading to a phenyl transfer in tegral of 2.539 eV, an on-site Coulomb energy of 10.06 eV and a relati ve error of 2.8%, compared with 7.4% using the standard values. We nex t optimise agreement for the long axis polarised optical transitions o f biphenyl with absorption data, leading to a bridging bond transfer i ntegral of 2.22 eV. (C) 1998 Elsevier Science B.V. All rights reserved .