CONVERGING THE SINGLE-REFERENCE COUPLED-CLUSTER EQUATIONS

A scheme for stabilizing the reduced linear equation method of solving the single-reference coupled system of equations is developed and implemented. When one or more secondary determinants become as important as the primary determinant in describing the chemical system, numerical instabilities frequently arise in the procedure of solving the coupled-cluster equations. This is avoided by "quasi-linearizing" certain non-linear terms in the equations and including them with the linear terms. A study on the LiH molecule with an internuclear separation of 9.045 au is used to demonstrate the effectiveness of this procedure.