Representation of the molecular electrostatic potential by a net atomic charge model

Abstract

Electrostatic potentials and Mulliken net atomic charges were calculated from STO-3G, 6-31G, and 6-31G* * SCF-MO wavefunctions for hydrogen fluoride, water, ammonia, methane, acetylene, ethylene, carbon dioxide, formaldehyde, methanol, formamide, formic acid, acetonitrile, diborane, and carbonate ion. In each case optimized net atomic charges (potential-derived charges) were also obtained by fitting the electrostatic potentials calculated directly from the wavefunctions in a shell enveloping the molecules outside of their van der Waals surfaces. The electrostatic potentials calculated from the potential-derived charge distributions were then compared with the defined quantum mechanical electrostatic potentials and with the electrostatic potentials of the Mulliken charge distributions.

A Transferable Intermolecular Potential for Nitramine Crystals

“…It has been shown previously [25,26] that the neglect of electron correlation in self-consistent wave functions overestimates the electrostatic interactions; however, this is mainly a scaling effect. Cox and Williams [25] have suggested that a scaling factor of 0.9 can be used to improve agreement between the calculated and experimental values of the dipole moments for a set of eight small molecules.…”

“…Cox and Williams [25] have suggested that a scaling factor of 0.9 can be used to improve agreement between the calculated and experimental values of the dipole moments for a set of eight small molecules. The same factor has been justified in a study of the electrostatic interactions of a dipeptide [26], as well as in a more recent work related to the role of electrostatic interactions in determining the crystal structures of polar organic molecules [10].…”

“…The procedure of uniformly scaling the HF charges, [10,25] decreases the differences to about 4.1%. It was also shown that this intermolecular potential correctly describes the order of stability of different phases.…”

Solvation effects on reactive intermediates: The benzyl radical and its clusters with Ar, N2, CH4, C2H6, and C3H8

“…The particular method we use is similar to that of Williams et al 36 First, the electrostatic potential is evaluated at specific grid points. The grid chosen is a simple 3-dimensional cubic grid with a spacing of 2.0 bohr between points.…”

“…A shell thickness of 4.0 bohr is employed for these calculations. 36 This value is chosen to maximize the number of points for the determination of charges, while simultaneously minimizing the errors introduced by assuming each point has equal weight. Third, a standard non-linear fitting routine is employed to obtain the final values of the charges 4 1 by setting the magnitude of the error in each point equal to its value.…”