In previous work by Yang. a method of overcoming the large phase cancellation problem in
calculating far wing off-diagonal matrix elements is discussed. The method based on solving
the Schrödinger equation along a contour in the complex plane has proven to be useful for
one-dimensional systems. In our present work we extend the technique to the case of three-
dimensional systems. We show how the method improves accuracy of the matrix element
calculations by reducing rapid oscillations of the integrand.