Modern valence bond theory

Modern valence bond theory describes molecular electronic structure with optimized, nonorthogonal valence-bond structures whose quantum-mechanical resonance interactions contribute to the total wavefunction.

Connect

Valence bond structure: A quantum state built around a particular pattern of electron pairing and bonding between atoms. Each optimized structure supplies one bonding pattern in the theory’s expansion of a molecule’s wavefunction.
Valence bond theory: A quantum-chemical approach that explains molecular bonds through localized electron pairing and combinations of bonding structures. Modern valence bond theory extends this broader framework with systematic optimization and computational methods.
Chemical reaction mechanism: A stepwise account of how reactants transform into products through bond changes and intermediates. Valence-bond descriptions can track changing bonding patterns along a reaction pathway.
Linus Pauling: An American chemist whose work established influential quantum-mechanical accounts of chemical bonding. Pauling helped make resonance and localized bonding central to the earlier valence-bond tradition.
Complete active space self-consistent field: A multiconfigurational method that optimizes orbitals and mixes all configurations within a chosen active orbital space. It treats static correlation through orbital configurations rather than selected valence-bond structures.
Resonance energy: The energy lowering associated with combining multiple electronic structures into a quantum state. Interaction among the theory’s structures can stabilize the molecular state beyond any single structure.
Resonance (chemistry): The quantum-mechanical contribution of multiple structures to one molecular electronic state. Resonance is represented explicitly through interactions among valence-bond structures.
Bond dissociation: The separation of bonded atoms or groups, characterized by the energy required to break a bond. Optimized valence-bond structures can describe how electronic character changes as a bond stretches.
Walter Heitler: A German physicist who, with Fritz London, applied quantum mechanics to the hydrogen molecule. The Heitler–London treatment supplied a foundational quantum account of covalent bonding.
Density functional theory: A quantum-chemical approach that calculates electronic properties from electron density and approximate energy functionals. It offers a widely used alternative to explicit wavefunction expansions in molecular calculations.