CPU implementation: The snippet of python code below illustrates how to use the CPU version. Basis functions on an atomic center (x i , y i , z i ) with the orbital exponent β i are grouped into shells of total angular momentum l i = n xi + n yi + n zi . Integrals for all angular momentum components of a shell are processed in one go so that intermediate results can be reused. The library defines the class PolarizationIntegral for evaluating individual integrals between shells. First, an integral object has to be created. Its constructor takes the data for the bra and ket shells as well as the parameters of the polarization operator as input: