Gaussian-2 (G2) Theory

Gaussian-2 theory is a composite technique in which a sequence of well-defined ab initio molecular orbital calculations is performed to arrive at a total energy of a given molecular species.¹ Geometries are determined using second-order Moller-Plesset perturbation theory. Correlation level calculations are done using Moller-Plesset perturbation theory up to fourth-order and with quadratic configuration interaction. Large basis sets, including multiple sets of polarization functions, are used in the correlation calculations. A series of additivity approximations makes the technique fairly widely applicable. G2 theory was originally tested on a total of 125 reaction energies, chosen because they have well-established experimental values. The test set includes has been expanded to include larger, more diverse molecules. This new test set is referred to as the G2/97 test set. It includes 148 enthalpies of formation, 88 ionization potentials, 58 electron affinities, and 8 proton affinities. The comprehensive set, which includes the original G2 test set, contains 302 entries.^2,3 Data for this test set are given in the web page.

1. "Gaussian-2 theory for molecular energies of first- and second-row compound" L.A. Curtiss, K. Raghavachari, G. W. Trucks, and J. A. Pople, Journal of Chemical Physics 94, 7221 (1991).

2. "Assessment of Gaussian-2 and Density Functional Methods for the Computation of Enthalpies of Formation" L. A. Curtiss, K. Raghavachari, P. C. Redfern, and J. A. Pople, Journal of Chemical Physics 106, 1063 (1997).

3. "Assessment of Gaussian-2 and Density Functional Methods for the Computation of Ionization Energies and Electron Affinities" L. A. Curtiss, P. C. Redfern, K. Raghavachari, and J. A. Pople, Journal of Chemical Physics, 109, 42 (1998).

For more information contact Larry Curtiss: e-mail: curtiss@anl.gov