Applications of semi-empirical quantum mechanical calculations to simple molecular systems.

Abstract

Quantum chemical calculations and molecular modeling have almost achieved the status of being regarded as an "experimental" tool. Selected properties of simple open-and closed-shell molecular systems containing nitrogen, sulfur, and oxygen have been studied using HyperChemTM. Structural and molecular properties are calculated in order to be able to evaluate the quality of results to be expected from this tool. Bond lengths, bond angles, dipole moments, the enthalpy of formation, and the first ionization potential have been calculated via semiempirical methods. Electron density, HOMO, and LUMO molecular orbital maps have been constructed. For the purpose of comparisons, calculations were carried out on a small sample of molecules using CNDO, INDO, MINDO/3, MNDO, and AM1 methods. All other calculations were carried out using the AM1 method.