Partitioning of the first-order reduced density matrix: description of functional groups

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

Londres

Workshop; 12th European Workshop on Quantum Systems in Chemistry and Physics (QSCP-XII); 2007

Royal Holloway University of London

The decomposition of molecular quantities into contributions associated to atoms or groups of atoms in a molecule has proven to be a suitable technique to describe chemical bondings and molecular properties. The partitioning of the N molecular electrons (population analysis), the partitioning of the spin <S2> and the electronic molecular energy partitioning are examples of this procedure. We have described partitionings of the first-order reduced density matrix corresponding to an N-electron system into first-order matrices associated with Bader atomic domains which have been denominated domain-restricted first-order reduced density matrices1,2. In this work we explore the suitability of the domain-restricted first-order reduced density matrices to describe the transferability3 of determined groups of atoms (functional groups). These matrices fulfill all the necessary and sufficient conditions to be representative of a physical subsystem, such as a determined region within a molecule and consequently, to perform local descriptions of the density. We evaluate the invariance of the electron density in the domains defined by an atomic cluster or group with different environments by means of the invariance of the eigenvalues and eigenvectors of the domain-rectricted first-order reduced density matrices describing those domains4. We report numerical results obtained in several series of compounds showing the suitability of our proposals to describe the main characteristics of the functional groups -CH3-, -CH2-, -OH, -NH2 and -CO-. These results provide nearly invariant features for these groups within different compounds although they allow one to detect the influence of the chemical environment around the functional group. Our results point out that the domain-rectricted first-order reduced density matrices are appropriate entities to identify functional groups and to assess from a rigorous physical point of view the intuitive concept of transferability. REFERENCES: 1 D.R. Alcoba, L. Lain, A. Torre and R.C. Bochicchio, J. Chem. Phys. 123, 144113 (2005) 2 D.R. Alcoba, R.C. Bochicchio, A. Torre and L. Lain, J. Phys. Chem. A 110, 9254 (2006) 3 P.W. Ayers, J. Chem. Phys. 113, 10886 (2000) 4 D.R. Alcoba, A. Torre, R.C. Bochicchio and L. Lain, Theor. Chem. Acc. 000, 0000 (2007)