Extended Basis Set Calculations of Atomization Energies: Comparison of Isogyric and Direct Results

With the development of software implementing quantum chemical techniques that employ energy gradient and Hessian data, and the concurrent increase of access to modern supercomputers, systematic studies of molecular structures and properties have become routine. Recently, several groups have reported efforts to compute accurate values of molecular heats of formation. People and coworkers described a study of first-row hydrides using full fourth- order perturbation theory with a variety of basis sets. In the studies of bond dissociation energies for a series of first-row diatomics. The results described in these papers indicated that fourth-order perturbation theory calculations using extended basis sets provided generally excellent results for sigma-bonded systems,with less accurate results obtained for multiply bonded systems. We described the results of a series of extended basis set Moller-Plesset perturbation theory calculations of a series of first row hydrides. Analysis of atomization energy prediction obtained employing the isogyric reaction technique demonstrates that third-order perturbation theory results are virtually indistinguishable from the results using a full forth-order calculations. (AW)