Subspace iteration techniques for the calculation of resonances using complex symmetric Hamiltonians

Abstract

We investigate and compare the performance of the Arnoldi and block-Davidson approaches for the calculation of selected eigenstates of complex symmetric Hamiltonians arising in the study of resonances. In the context of the block-Davidson scheme, both the “natural” complex symmetric subspace projection and the unsymmetric orthogonal projection are studied. The latter is found to possess the best convergence properties in realistic examples, clearly outperforming the other methods.