Any order imaginary time propagation method for solving the Schrödinger equation

The eigenvalue-function pair of the 3D Schrödinger equation can be efficiently computed by use of high order, imaginary time propagators. Due to the diffusion character of the kinetic energy operator in imaginary time, algorithms developed so far are at most fourth-order. In this work, we show that for a grid based algorithm, imaginary time propagation of any even order can be devised on the basis of multi-product splitting. The effectiveness of these algorithms, up to the 12 order, is demonstrated by computing all 120 eigenstates of a model C60 molecule to very high precisions. The algorithms are particularly useful when implemented on parallel computer architectures.