Density functional study of small molecules and transition-metal carbonylsusing revised PBE functionals

We have implemented the generalized gradient approximation (GGA) exchange-c orrelation functional suggested by Perdew, Burke, and Ernzerhof(PBE) and tw o of its recent revisions, revPBE and RPBE, in the program ParaGauss, which is a new version of the LCGTO-FF (fitting function) approach designed for parallel computers. With these new functionals, we investigated a test suit e of 19 small molecules as well as the transition-metal carbonyls of Cr, Fe , and Ni using very flexible Gaussian-type orbital (GTO) basis sets. Both r evised PBE functionals yield very similar results for the atomization energ ies of small molecules, improved over those obtained with conventional GGAs (BP, PW91, PBE) as judged by the average absolute error (5 kcal/mol reduce d from 8 kcal/mol). Atomization energies of revised PEE functionals are on the average 7 kcal/mol smaller than those of conventional GGAs, consistent with an average bond elongation by about 0.006 Angstrom relative to these G GAs. Revised PEE functionals yield bond distances on average 0.016 Angstrom longer than experiment. With revised PEE functionals, the first carbonyl d issociation energies of Cr(CO)(6), Fe(CO)(5), and Ni(CO)(4) are calculated in excellent agreement with experiment whereas structures are calculated Ve ry similar to those of conventional GGAs. (C) 1999 John Wiley & Sons, Inc.