INTRAMOLECULAR ELECTROSTATIC INTERACTIONS STUDIED BY CUMULATIVE ATOMIC MULTIPOLE MOMENT EXPANSION WITH IMPROVED CONVERGENCE

A novel approach allowing the estimation of intramolecular electrostat ic interactions has been applied to evaluate torsional barriers for mo del HO-OH, CH3-CH, and H2FSi-SiFH2 systems. Interactions between rotat ed fragments have been estimated from cumulative atomic multipole mome nts (CAMM) calculated for frozen molecular fragments and compared with corresponding ab initio results. The exclusion of all intersegment co mponents of the global density matrix resulted in considerably improve d convergence of the moment-truncated expansion. CAMM generated for di fferent conformers yield similar results, indicating reasonable transf erability of frozen fragment CAMM. The close qualitative and quantitat ive correspondence between atomic multipole and non-empirical ab initi o results indicates the dominant electrostatic nature of the intramole cular torsional barriers.