COMPUTATION OF INTERIOR EIGENSTATES OF LARGE MATRICES USING THE QUASI-ADIABATIC EVOLUTION OF INSTANTANEOUS EIGENVECTORS

A two-stage iterative scheme is proposed to handle a central problem o f molecular dynamics, the computation of interior eigenvalues of large Hamiltonian matrices. The proposed method involves an initial propaga tion process for a time-dependent wave operator which is then inserted in an iterative process (recursive distorted wave approximation or si ngle cycle method) to yield the exact stationary wave operator. The me rits of the wave operator formalism for quasiadiabatic propagation are analyzed, and possible improvements such as the use of partial adiaba tic representations and spectral filters, are outlined. The proposed a lgorithm is applied to the test case of two coupled oscillators with v ariable coupling strength, and yields accurate results even with small switching times. (C) 1995 American Institute of Physics.