Spin structure and properties of the correlation matrices corresponding to pure spin states: Controlling the S-representability of these matrices

In this paper we investigate the S‐representability conditions that a two‐body correlation matrix must satisfy when the N‐electron system is in a given pure spin state. To purify a trial two‐body correlation matrix, the N‐ and S‐representability conditions are combined in a computational procedure for singlet states. This procedure is tested in two calculations on a molecular system and the results are discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005