For the calculation of the transmission coefficient of non-linear energy
barriers, the stationary one-dimensional SCHRÖDINGER equation must be solved. To
allow an easy extension to two- or three-dimensional problems, a
multi-dimensional SCHRÖDINGER solver based on the finite-difference
discretization has been developed. For the calculation of the transmission
coefficient using the QTBM (see Section 3.5.4) it is necessary to solve
SCHRÖDINGER's equation with open boundary conditions, while for the evaluation of
tunneling from quasi-bound states as described in Section 3.6.3 it is necessary
to solve the same problem with closed boundary conditions. Therefore, a solver
which allows flexible treatment of both cases has been developed.