Convergence improvement for coupled cluster calculations

Authors: N. Mosyagin (Petersburg Nuclear Physics Institute), E. Eliav, U. Kaldor (Tel Aviv
Comments: 7 pages, IOPP style
Subj-class: Chemical Physics

     Convergence problems in coupled-cluster iterations are discussed, and a new iteration
     scheme is proposed. Whereas the Jacobi method inverts only the diagonal part of the
     large matrix of equation coefficients, we invert a matrix which also includes a relatively
     small number of off-diagonal coefficients, selected according to the excitation
     amplitudes undergoing the largest change in the coupled cluster iteration. A test case
     shows that the new IPM (inversion of partial matrix) method gives much better
     convergence than the straightforward Jacobi-type scheme or such well-known
     convergence aids as the reduced linear equations or direct inversion in iterative
     subspace methods.

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