Energy-independent effective interactions: Analytic expressions for the required G-matrix energy derivatives

Abstract

In a recent paper it has been shown that the successful application of the method of Suzuki and Lee for calculating an energy-independent effective interaction requires that the energy derivatives of the G-matrix be calculated accurately. In that work methods by which these derivatives may be calculated analytically in problems where P, the projection operator which defines the active space, can be written in the center-of-mass and relative coordinates were presented. In this work we extend the applicability of the theory by presenting analytic expressions for calculating the energy derivatives of the G-matrix elements obtained by the method of Barrett et al. Convergence properties of the iterative processes by which the effective interaction is calculated are investigated and guidelines for choosing the starting energy are given. As an example of its use, the theory is applied to the ground state and low-lying resonances of 4He.