Generalized spin orbital calculations of spin-frustrated molecules

It is difficult to consider the closed chain which contains odd-number spin sites under the UHF approximation because of the spin frustration. The gen eralized HF (GHF) method, which deals with generalized spin orbitals (GSO) of the form phi (alpha)alpha + phi (beta)beta, can provide a characteristic electronic state with noncollinear spin configuration. In this article, ex plicit expressions of effective exchange integrals (J(ab) values) based on GHF solutions were derived for the closed chain which contains odd-number s pin sites. The lab values were calculated for simple systems such as equila teral triangular H-3, equilateral pentagonal H-5, and so on. Furthermore, s pin correlations and electron correlations of the H3 Molecule are discussed by using visualization methods for electron correlations. (C) 2001 John Wi ley & Sons, Inc.