A new rapid method for orbital localisation

Abstract

A new method is described which allows the rapid construction of localised molecular orbitals from eigenvector matrices and for a single-determinant wavefunction stemming from any quantum-chemical calculation. The essential modification over present methods is the application of the ZDO (zero differential overlap) approximation. A practical scheme is presented which facilitates applications of the method to complex molecular systems. As an illustration of the method, it is applied to a series of systems where the bonding is of the “classical” type (nitrogen, carbon dioxide, ethane, benzene, pyridine, neo-pentane and ethylene), of the “non-classical” type (diborane, B₄Cl₄, B₁₂H^2–₁₂ and cis-C₂B₄H₆) and a solid (polyethylene). The results give an informative picture of the bonding in these molecules. Two new quantities, the bond number and the lone-pair character, are defined quantitatively.