ELECTRONIC-STRUCTURE AND PROPERTIES OF MCO AND M(5)CO CARBONYLS (M=FE,NI,CU) BY DENSITY-FUNCTIONAL METHODS

Density functional theory (DFT) calculations of the electronic structu re and properties of Fe, Ni, and Cu carbonyls with one and five transi tion-element atoms are reported, due to their importance in heterogene ous catalysis (especially in Fischer-Tropsch synthesis). The local den sity approximation (LDA) with the Vosko-Wilk-Nussain (VWN) correlation functional as well as the generalized gradient approximation (GGA) us ing Becke's 1988 exchange functional and Perdew's 1986 correlation fun ctional (BP method) were applied to the study of the dusters using a t riple-zeta plus polarization (TZP) basis set. Triplet and quintuplet s tates for FeCO, singlet and triplet for NiCO, and doublet for CuCO wer e considered, and optimization of energy at the LDA/BP level for these cases was done. Dissociation energies in M and CO fragments, frequenc ies, and population analysis were performed. Geometry optimization of the distance between the C atom and the clusters M(5) (with geometries taken from the crystals) were carried out and the dissociation energy in fragments M(5) and CO as well as population analysis at the optimi zed geometries were also done. Comparison between our results and some others published using ab initio and density functional methods were performed. (C) 1996 John Wiley & Sons, Inc.