Determination of Three-center Bond Indices from Population Analyses: a Fuzzy Atom Treatment

A. TORRE; D.R. ALCOBA; L. LAIN; R.C. BOCHICCHIO

Cartago

Workshop; 10th European Workshop on Quantum Systems in Chemistry and Physics (QSCP-X); 2005

Commission Europeenne Cost D9; Academy Of Sciences Beit Al-Hikma; Faculte Des Sciences De Tunis

The techniques of population analysis carry out partitionings of the N electrons of a system into different contributions that are assigned to atoms, atomic regions or group of atoms, allowing one to describe conventional two-center bondings and more complex bonding patterns (multicenter bondings). Within the techniques of population analysis, the Mulliken-type treatments perform the analysis in the Hilbert space whereas in the atoms in molecules (AIM) theory the electrons are assigned to disjunct domains of the physical space. An alternative scheme of physical space decomposition is based on the use of the fuzzy atom procedure in which the atomic regions have no sharp boundaries. This procedure has been applied recently to describe two-center bond orders [1]. The aim of this work is to extend the applications of the fuzzy atom treatment by studying its ability to describe multicenter bond indices, particularly the three-center ones. To achieve this purpose we have adapted the mathematical framework of our previously reported studies [2] on multicenter bondings to the fuzzy atom approach. The obtained algorithms, which are valid at any level of theory, have been applied at correlated level within configuration interaction wave functions with single and double excitations. To perform test calculations within the fuzzy atom scheme, we chose two series of selected systems, according to the expected presence (or absence) of three-center bondings [3]. We describe the systems H3+, B2H6, allyl cation, allyl anion, CO2 and N3- in which the existence of three-center bondings is commonly accepted. Similarly, we report results for the systems H2O, NH3, CH4 and C2H6 which fit in with the classical two-center model. The results found show that this method detects three-center bondings for the compounds of the first series, demanding a lower computational cost than the Mulliken and AIM procedures. The description of the second series of compounds also turns out to be satisfactory, providing negligible values for three-center indices. REFERENCES: [1] I. Mayer and P. Salvador, Chem. Phys. Lett. 383, 368 (2004) [2] L. Lain, A. Torre and R.C. Bochicchio, J. Phys. Chem. A 108, 4132 (2004) [3] A. Torre, D.R. Alcoba, L. Lain and R.C. Bochicchio, J. Phys. Chem. A 109, 0000 (2005)