USING A FITTED ELECTRONIC DENSITY TO IMPROVE THE EFFICIENCY OF A LINEAR COMBINATION OF GAUSSIAN-TYPE ORBITALS CALCULATION

A molecule's electronic density can be accurately fitted in a divide-a nd-conquer fashion. This fitting procedure scales linearly with system size and becomes more efficient than the conventional scheme for rela tively small systems (approximate to 40 atoms for one-dimensional syst ems) and is only marginally more expensive for the smallest systems. A system's electronic density is partitioned into a sum of subsystem co ntributions. This partitioning scheme is used to construct an approxim ate density that can ease the burden associated with various calculati ons. Contributions arising from faraway subsystems are calculated usin g their fitted subsystem densities, while contributions arising from n earby subsystems are more accurately calculated using their exact subs ystem densities. Its application to the calculation of the molecular e lectrostatic potential is shown. Though this scheme has been implement ed and tested within a density functional program, the ideas presented may be used in any quantum mechanical program.