title: Charge-Shift Bonding Emerges as a Distinct Electron-Pair Bonding Family from Both Valence Bond and Molecular Orbital Theories.
abstract: The charge-shift bonding (CSB) concept was originally discovered through valence bond (VB) calculations. Later, CSB was found to have signatures in atoms-in-molecules and electron-localization-function and in experimental electron density measurements. However, the CSB concept has never been derived from a molecular orbital (MO)-based theory. We now provide a proof of principle that an MO-based approach enables one to derive the CSB family alongside the distinctly different classical family of covalent bonds. In this bridging energy decomposition analysis, the covalent-ionic resonance energy, RECS, of a bond is extracted by cloning an MO-based purely covalent reference state, which is a constrained two-configuration wave function. The energy gap between this reference state and the variational TCSCF ground state yields numerical values for RECS, which correlate with the values obtained at the VBSCF level. This simple MO-based method, which only takes care of static electron correlation, is already sufficient for distinguishing the classical covalent or polar-covalent bonds from charge-shift bonds. The equivalence of the VB and MO-based methods is further demonstrated when both methods are augmented by dynamic correlation. Thus, it is shown from both MO and VB perspectives that the bonding in the CSB family does not arise from electron correlation. Considering that the existence of the CSB family is associated also with quite a few experimental observations that we already reviewed ( Shaik , S. , Danovich , D. , Wu , W. , and Hiberty , P. C. Nat. Chem. , 2009 , 1 , 443 - 449 ), the new bonding concept has passed by now two stringent tests. This derivation, on the one hand, supports the new concept and on the other, it creates bridges between the two main theories of electronic structure.
authors.affiliation: The State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University , Xiamen, Fujian 361005, China.
authors.forename: Huaiyu
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Institute of Chemistry and The Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University , Jerusalem 91904, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Danovich
authors.affiliation: The State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen University , Xiamen, Fujian 361005, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wu
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06 , UMR 7616, LCT, F-75005, Paris, France.|CNRS , UMR 7616, LCT, F-75005, Paris, France.
authors.forename: Benoît
authors.initials: B
authors.lastname: Braïda
authors.affiliation: Laboratoire de Chimie Physique, Groupe de Chimie Théorique, Université de Paris-Sud, CNRS UMR 8000 , 91405 Orsay, France.
authors.forename: Philippe C
authors.initials: PC
authors.lastname: Hiberty
authors.affiliation: Institute of Chemistry and The Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University , Jerusalem 91904, Israel.
authors.forename: Sason
authors.initials: S
authors.lastname: Shaik