Improved simple protocols to calculate hydrocarbon enthalpies of formation from ab initio total energies

An extension of previous simple protocols to convert Hartree-Fock ab initio electronic energies for hydrocarbons to precise enthalpies of formation is given. The multilinear regression procedure resorts to the use of quadratic relations involving the number of carbon and hydrogen atoms and molecular total energies calculated at the 6-31 G* basis set level as independent variables. Results are somewhat better than those obtained via linear equations. Some special features regarding the energy range comprising the Delta H-f(o)(g) values and the very different nature of the chosen set of 65 compounds are discussed in order to assess the value of these improved simple protocols. (C) 1997 Elsevier Science Ltd.