Numerical and non-numerical methods in chemistry

1. Theoretical chemistry uses at present two types of methods for calculating properties of molecules by solving the Schrödinger equation applied to many bodies (electrons and nuclei) approximately:(i) Semiempirical methods: Hückel molecular orbitals (practically abandoned nowadays), extended Hückel method (Roald Hoffmann), CNDO, INDO, MINDO, MNDO, where Neglect of Differential Overlap may be Complete, Intermediate, etc. To match experimental values, the methods use empirical parameters which again differ according to author and method; the Pariser-Parr-Pople parametrization is largely employed, but the MINDO and MNDO methods use the Dewar parametrization. Actually, most of these methods, e.g. CNDO, MINDO and MNDO have several versions distinguished by numbers, i.e. CNDO/2.