Discrete transparent boundary conditions for the Schrödinger equation: fast calculation, approximation, and stability

We propose a way to efficiently treat the well-known transparent boundary conditions for the Schrödinger equation.Our approach is based on two ideas: to write out a discrete transparent boundary condition (DTBC) using the Crank-Nicolson finite difference scheme for the governing equation, and to approximate the discrete convolution kernel of DTBC by sum-of-exponentials for a rapid recursive calculation of the convolution.We prove stability of the resulting initial-boundary value scheme, give error estimates for the considered approximation of the boundary condition, and illustrate the efficiency of the proposed method on several examples.