Ab initio calculations on large molecules using molecular fragments: Comparison of charge distribution and molecular electrostatic potential for ethyl chlorophyllide a and related molecules

Abstract

An analysis of the electronic charge distributions of porphine and chlorin, their magnesium-substituted analogs, and ethyl chlorophyllide a has been carried out, using point-charge and symmetrically orthogonalized representations of ab initio molecular fragment SCF-MO wave functions. The results indicate that both representations provide essentially identical descriptions.Molecular electrostatic potential calculations have also k n carried out using the point-charge representation and from the wave function directly. Both approaches are in good agreement in regions beyond the van der Waals radius of the various atoms in the molecule.

Fragmentation Methods: A Route to Accurate Calculations on Large Systems

“…Klessinger and McWeeny in 1965 in their Group SCF (self-consistent field) method suggested defining molecular orbital groups to reduce the scaling of SCF. Christoffersen and co-workers − employed localized molecular orbitals (LMOs) and floating spherical Gaussian orbitals (FSGO) to separate the subdensity matrices of fragments that are then summed to obtain the total density and (thereby) desired properties. The method has been applied with success to many species, including molecules of biological importance.…”