Method of calculating matrix elements and cross sections with wave functions with definite angular momentum

A method is proposed for calculating the matrix elements and cross sections with a wave function with definite angular momentum. The method consists of calculating the matrix element in which the function with definite angular momentum is replaced by the function $\exp(i\mathbf k\mathbf r-\eta r)$ with subsequent differentiation of the result with respect to $\eta$ and taking of the gradients with respect to $\mathbf k$ in accordance with $\text{Eq}$.(5). The method is illustrated for the example of the calculation of the photoeffect cross section from an arbitrary shell without the dipole approximation.