Momentum-matrix-element calculation using pseudopotentials

A method of calculating momentum matrix elements using pseudopotentials is proposed. A core-repair term is introduced in the method to eliminate errors created by the poor representation of the atomic core region by the pseudopotentials. Calculating the core-repair term requires fewer computational resources especially for separable form pseudopotentials. This approach is suitable for non-norm-conserving pseudopotentials as well as general norm-conserving pseudopotentials. The effectiveness of the method is verified for various isolated atoms. The method is also applied to calculate momentum matrix elements for planar polysilane, planar siloxene, gallium arsenide, and gallium nitride.