Atomic Multipole Expansions of Molecular Charge Densities. Electrostatic Potentials
The molecular electrostatic potential has been shown to be a very useful tool for understanding the reactivities of molecules with ions or polar molecules1 and the structure and energetics of intermolecular complexes, including hydrogen bonded complexes.2 The electrostatic potential can be obtained as the by-product of a molecular orbital calculation in the form of a large table of numbers.3 A considerable computational advantage would be obtained if this information could be compressed into analytical form, and a large amount of effort has gone into the search for appropriate representations. For instance, Bonaccorsi, Scrocco and Tomasi4 have shown how one can resolve molecular electrostatic potentials into sums of contributions from fragments within the molecule; the fragment contributions are approximately transferable, allowing one to construct the potential for a large molecule without first performing a molecular orbital calculation on that molecule. Kollman5 has also addressed the problem of obtaining the potential without a wave function and has produced a family of point-charge models for which the necessary inputs are experimental bond lengths, bond angles, and dipole moments, atomic electronegativities, and van der Waals radii. These point-charge distributions produce electrostatic potentials at suitable reference points which are in reasonable accord with the potentials obtained from wave functions.
KeywordsWave Function Electrostatic Potential Quadrupole Moment Molecular Electrostatic Potential Multipole Moment
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