EVALUATION OF DENSITY-FUNCTIONAL THEORY IN THE BOND RUPTURE OF OCTANE

Density functional methods at the 6-31G() level are applied to the ru pture of n-octane into methyl-heptyl, ethyl-hexyl, propyl-pentyl, and butyl-butyl radical fragments. The energetics of the radicals at UMP3, UMP2/6-31G()//UHF/6-31G(*) (hereafter referred to as UMP), are compa red to UB3LYP/6-31G() results (referred to as UB). Although the UMP a pproach matches additivity energies to within 5 kcal/mol, it fails to mimic the overall energetic trend. The UB energies agree with additivi ty estimates and trends to within 1-2 kcal/mol and radical entropies d eviate by only 2 e.u. from available experimental data. (C) 1998 John Wiley & Sons, Inc.