Noniterative implementation of the Green-function-based open boundary condition for FEM

The paper describes a noniterative implementation of the Green function based open boundary condition (GBC) for the FEM model. The earlier approach used the iterative update of the potential on the open boundary. The method presented here avoids iteration at the cost of more complicated implementation, similar to periodicity boundary conditions. The detailed procedure which allows us to keep a symmetric matrix of the system of algebraic equations is presented. The relations between GBC and the other FEM open boundary procedures are briefly discussed.