CENTRAL OR DISTRIBUTED MULTIPOLE MOMENTS - ELECTROSTATIC MODELS OF AROMATIC DIMERS

Multipole moments up to rank six are calculated at the SCF level for sym-triazine and 1,3,5-trifluorobenzene. Staggered face-to-face configurations of the homodimers are stabilised by both electrostatic and dispersion interactions. Low-order central multipole models fail to show the electrostatic attraction; high-order central multipole expansions are strongly divergent. Distributed multipoles derived either by fitting to ab initio central multipoles, or by analysis of the electron density, predict the correct orientational minimum and give reasonable estimates of electrostatic interaction energies.