Scaled effective one-electron method based on G2 theory: Results for aliphatic alkane molecules

An effective one-electron model was constructed and parameterized using G2 molecular total energies. For aliphatic alkane molecules, the calculated gas-phase standard heats of formation closely matched the experimental values. For 63 molecules, the average absolute deviation and maximum absolute deviation were 0.83 and 3.70 kcal/mol, respectively. The results show that it is important to perform full conformational analysis and to treat the torsional vibrations as free internal rotations at higher temperatures. The calculated standard heats of formation were also compared with those obtained from revised group additivity values and via the AM1 method. The optimized equilibrium molecular geometries were even better than the RHF/6-31G* ones.