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

Density functional theory is tested on a large ensemble of model compo unds containing a wide variety of functional groups to understand bett er its ability to reproduce experimental molecular geometries, relativ e conformational energies, and dipole moments. We find that gradient-c orrected density functional methods with triple-zeta plus polarization basis sets reproduce geometries well. Most bonds tend to be approxima tely 0.015 Angstrom longer than the experimental results. Bond angles are very well reproduced and most often fall within a degree of experi ment. Torsions are, on average, within 4 degrees of the experimental v alues. For relative conformational energies, comparisons with Hartree- Fock calculations and correlated conventional ab initio methods indica te that gradient-corrected density functionals easily surpass the Hart ree-Fock approximation and give results which are nearly as accurate a s MP2 calculations.