Configuration Interaction and the calculation of E.S.R. and N.M.R. coupling constants.

A scheme is presented for a computer program using the Configuration Interaction method. To make the program as flexible as possible, lists of spin-configurations over RHF molecular orbitals are kept. These separate configurations for the alpha and beta spins can be combined to give the total configurations as and when necessary. It is shown how advantage may be taken of the internal bit structure of a computer word so as to store the spin-configurations as a binary pattern, which provides economical storage, and how information can then be extracted from them by means of the computer's logical machine instructions. The Configuration Interaction method is applied to the calculation of magnetic resonance properties. The Electron Spin Resonance hyperfine coupling constants of the [special character omitted]-radicals NH2, BH3-, CH3 and NH3+ and the a-radicals BeOH and BeH are studied using a range of basis sets and allowing various levels of excitations to be included in the CI. Rather more tentative results are presented for the Nuclear Magnetic Resonance coupling constants of CH4, NH3, H2O and HF using only minimal basis sets.