Stability conditions for the coupled cluster equations

The coupled Cluster (CC) equations are Studied from the point of view of the stability of their solution. The nonlinear nature of these equations may lead to undesired iteration properties including chaotic solutions. Iterations of various types (convergent, oscillatory, chaotic or divergent) are identified by the eigenvalues of the stability (Jacobi) matrix at the fixed points. Explicit (orbital) form of the stability matrix is obtained for the CCSD case, and the various iteration domains are investigated as a function of the control (damping) parameter of the C-C iteration. The case of the BeH2 molecule at various nuclear arrangements is chosen as a numerical example. (c) 2008 Wiley Periodicals, Inc.