USE OF ABINITIO QUANTUM-MECHANICS CALCULATIONS IN GROUP CONTRIBUTION METHODS .1. THEORY AND THE BASIS FOR GROUP IDENTIFICATIONS

Group contribution methods are powerful tools for estimating the thermophysical and thermodynamic properties of pure components and mixtures from experimental data on related substances. Among the problems with current group contribution methods is that there is no theoretical basis for defining functional groups and no a priori way of determining when a group contribution prediction may be in error. Here we show that, on the basis of quantum mechanical ab initio molecular orbital calculations on single molecules, we can develop a simple theoretical basis for defining functional groups. Further, by "supermolecule" calculations involving two or more molecules, we can identify situations in which group contribution methods may fail.