MATRIX-ELEMENTS OF U(2N) GENERATORS IN A MULTISHELL SPIN-ORBIT BASIS - II - THE 2-SHELL NONZERO SHIFT ACCS AND U(2N) GENERATOR MES

This is the second in a series of articles whose ultimate goal is the evaluation of the matrix elements (MEs) of the U(2n) generators in a m ultishell spin-orbit basis. This extends the existing unitary group ap proach to spin-dependent configuration interaction (CI) and many-body perturbation theory calculations on molecules to systems where there i s a natural partitioning of the electronic orbital space. As a necessa ry preliminary to obtaining the U(2n) generator MEs in a multishell sp in-orbit basis, we must obtain a complete set of adjoint coupling coef ficients for the two-shell composite Gelfand-Paldus basis. The zero-sh ift coefficients were obtained in the first article of the series. in this article, we evaluate the nonzero shift adjoint coupling coefficie nts for the two-shell composite Gelfand-Paldus basis. We then demonstr ate that the one-shell versions of these coefficients may be obtained by taking the Gelfand-Tsetlin limit of the two-shell formulas. These c oefficients,together with the zero-shift types, then enable us to writ e down formulas for the U(2n) generator matrix elements in a two-shell spin-orbit basis. Ultimately, the results of the series may be used t o determine the many-electron density matrices for a partitioned syste m. (C) 1998 John Wiley & Sons, Inc.