CNDO/2

CNDO is the abbreviation for Complete Neglect of Differential Overlap, one of the first semi empirical methods in quantum chemistry. It uses two approximations:

CNDO/2 is the main version of CNDO. The method was first introduced by John Pople and coworkers.

Background

An earlier method was Extended Hückel method, which explicitly ignores electron-electron repulsion terms. It was a method for calculating the electronic energy and the molecular orbitals. CNDO/1 and CNDO/2 were developed from this method by explicitly including the electron-electron repulsion terms, but neglecting many of them, approximating some of them and fitting others to experimental data from spectroscopy.

Methodology

Quantum mechanics provides equations based on the Hartree–Fock method and the Roothaan equations that CNDO uses to model atoms and their locations. These equations are solved iteratively to the point where the results do not vary significantly between two iterations. It is noteworthy that CNDO does not involve knowledge about chemical bonds but instead uses knowledge about quantum wavefunctions.