Application of Xα multiple-scattering theory to planar organic molecules: One-electron properties and ionization potentials of benzene, pyridine, pyrazine, pyrrole, and imidazole

Abstract

Xα multiple scattering wave functions and molecular properties are reported for benzene, pyridine, pyrazine, pyrrole, and imidazole. The calculations demonstrate that useful results can be obtained for planar conjugated organic molecules with the Xα method. Values are obtained for ionization potentials and one electron properties, including dipole and quadrupole moments, diamagnetic susceptibilities and nuclear quadrupole coupling constants. In general the results are in better agreement with experiment than minimum basis set Hartree–Fock calculations; this generalization is not true for molecular properties that are dominated by hydrogen atoms, such as deuteron quadrupole coupling constants. The sensitivity of the results to changes in sphere overlap is studied in detail for pyridine and it is found that useful accuracy can be achieved over a fairly broad range of overlap parameters. Calculated ionization potentials agree well with recent assignments of the photoelectron spectra, except for the relative ordering of π and nitrogen lone-pair orbitals. This difference is analysed in terms of correlation effects in lone-pair ionizations. As part of the comparisons, detailed tabulations of one-electron properties and ionization potentials obtained from experiments and other calculations are provided.