A Combined Charge and Energy Decomposition Scheme for Bond Analysis

In the present study we have introduced a new scheme for chemical bond analysis by combining the Extended Transition State (ETS) method [ Theor. Chim. Acta 1977, 46, 1 ] with the Natural Orbitals for Chemical Valence (NOCV) theory [ J. Phys. Chem. A 2008, 112, 1933 ; J. Mol.

2007, 13, 347 ]. The ETS-NOCV charge and energy decomposition scheme based on the Kohn-Sham approach makes it not only possible to decompose the deformation density, Δρ, into the different components (such as σ, π, δ, etc.) of the chemical bond, but it also provides the corresponding energy contributions to the total bond energy. Thus, the ETS-NOCV scheme offers a compact, qualitative, and quantitative picture of the chemical bond formation within one common theoretical framework. Although, the ETS-NOCV approach contains a certain arbitrariness in the definition of the molecular subsystems that constitute the whole molecule, it can be widely used for the description of different types of chemical bonds. The applicability of the ETS-NOCV scheme is demonstrated for single (H3X-XH3, for X = C, Si, Ge, Sn) and multiple (H2X═XH2, H3CX≡XCH3, for X = C, Ge) covalent bonds between main group elements, for sextuple and quadruple bonds between metal centers (Cr2, Mo2, W2, [Cl4CrCrCl4](4-)), and for double bonds between a metal and a main group element ((CO)5Cr═XH2, for X = C, Si, Ge, Sn). We include finally two applications involving hydrogen bonding. The first covers the adenine-thymine base pair and the second the interaction between C-H bonds and the metal center in the alkyl complex.