title: HEAT: High accuracy extrapolated ab initio thermochemistry.
abstract: A theoretical model chemistry designed to achieve high accuracy for enthalpies of formation of atoms and small molecules is described. This approach is entirely independent of experimental data and contains no empirical scaling factors, and includes a treatment of electron correlation up to the full coupled-cluster singles, doubles, triples and quadruples approach. Energies are further augmented by anharmonic zero-point vibrational energies, a scalar relativistic correction, first-order spin-orbit coupling, and the diagonal Born-Oppenheimer correction. The accuracy of the approach is assessed by several means. Enthalpies of formation (at 0 K) calculated for a test suite of 31 atoms and molecules via direct calculation of the corresponding elemental formation reactions are within 1 kJ mol(-1) to experiment in all cases. Given the quite different bonding environments in the product and reactant sides of these reactions, the results strongly indicate that even greater accuracy may be expected in reactions that preserve (either exactly or approximately) the number and types of chemical bonds.
authors.affiliation: Department of Theoretical Chemistry, Eötvös Loránd University, P.O. Box 32, H-1518 Budapest, Hungary.
authors.forename: Attila
authors.initials: A
authors.lastname: Tajti
authors.forename: Péter G
authors.initials: PG
authors.lastname: Szalay
authors.forename: Attila G
authors.initials: AG
authors.lastname: Császár
authors.forename: Mihály
authors.initials: M
authors.lastname: Kállay
authors.forename: Jürgen
authors.initials: J
authors.lastname: Gauss
authors.forename: Edward F
authors.initials: EF
authors.lastname: Valeev
authors.forename: Bradley A
authors.initials: BA
authors.lastname: Flowers
authors.forename: Juana
authors.initials: J
authors.lastname: Vázquez
authors.forename: John F
authors.initials: JF
authors.lastname: Stanton