Energy Decompositions According to Physical Space Partitioning Schemes

D.R. ALCOBA; L. LAIN; A. TORRE; 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 study of the decompositions of the electronic energy into contributions associated with each atom or group of atoms in a molecule presents a great interest. An appropriate partitioning scheme may enable one to identify the intramolecular bondings and to perform calculations of the bonding strenghts between the atoms that constitute a determined system. Several recent works related with energy partitionings have been reported as within a Mulliken type scheme [1], in which the partitioning is caried out in the Hilbert space spanned by the basis function set,  as within methods that partition the three-dimensional space [2]. This work proposes a simple scheme to perform decompositions of the electronic molecular energy according to partitionings of the three-dimensional space. A suitable formulation of the overlap integrals leads to the decomposition of the molecular energy into one- and two-domain terms [3]. Two methods have been developed, providing suitable mathematical algorithms. The first one carries out a formulation of the overlap integrals according to the theory of atoms in molecules of Bader, in which the real space is decomposed into disjunct atomic domains. In a second procedure the overlap integrals are calculated through a fuzzy atom technique, in which the space is decomposed into overlapping atomic domains. Simple systems (H2), hydrocarbons with different bond orders (CH4, C2H6, C6H6, C2H4 and C2H2) and some second-row hydrides (NH3, H2O and HF) have been chosen to test this methodology. The calculations have been performed at the Hartree-Fock level although the framework of our algorithms can be developed at any level of theory (correlated and uncorrelated wave functions). The results arising from both methods provide an adequate description of the chemical features of the studied molecules and are comparable with those obtained in previous reported studies that require a much higher computational effort. REFERENCES: [1] I. Mayer, Chem. Phys. Lett. 382, 265 (2003) [2] P. Salvador and I. Mayer, J.Chem. Phys. 120, 5046 (2004) [3] D.R. Alcoba, A. Torre, L. Lain and R.C. Bochicchio, J. Chem. Phys. 122, 074102 (2005)