CALCULATION OF MOLECULAR GEOMETRIES, RELATIVE CONFORMATIONAL ENERGIES, DIPOLE-MOMENTS, AND MOLECULAR ELECTROSTATIC POTENTIAL FITTED CHARGES OF SMALL ORGANIC-MOLECULES OF BIOCHEMICAL INTEREST BY DENSITY-FUNCTIONAL THEORY

Density functional theory is tested on a large ensemble of model compounds containing a wide variety of functional groups to understand better its ability to reproduce experimental molecular geometries, relative conformational energies, and dipole moments. We find that gradient-corrected density functional methods with triple-zeta plus polarization basis sets reproduce geometries well. Most bonds tend to be approximately 0.015 Angstrom longer than the experimental results. Bond angles are very well reproduced and most often fall within a degree of experiment. Torsions are, on average, within 4 degrees of the experimental values. For relative conformational energies, comparisons with Hartree-Fock calculations and correlated conventional ab initio methods indicate that gradient-corrected density functionals easily surpass the Hartree-Fock approximation and give results which are nearly as accurate as MP2 calculations.