Gradient symplectic algorithms for solving the Schrödinger equation with time-dependent potentials

We show that the method of factorizing the evolution operator to fourth order with purely positive coefficients, in conjunction with Suzuki’s method of implementing time-ordering of operators, produces a new class of powerful algorithms for solving the Schrodinger equation with time-dependent potentials. When applied to the Walker–Preston model of a diatomic molecule in a strong laser field, these algorithms can have fourth order error coefficients that are three orders of magnitude smaller than the Forest–Ruth algorithm using the same number of fast Fourier transforms. Compared to the second order split-operator method, some of these algorithms can achieve comparable convergent accuracy at step sizes 50 times as large. Morever, we show that these algorithms belong to a one-parameter family of algorithms, and that the parameter can be further optimized for specific applications.