The package employed in the numerical implementation of expressions in this work was Psi4NumPy . It is an interactive quantum-chemical environment designed for method development, rapid prototyping of new expressions and educational purposes. The package relies on Psi4 , an open-source quantum-chemical program, and its efficient computational kernel. In the case of this work, Hartree-Fock calculations for the monomers were carried out using Psi4, as well as all calculations of the one-and two-electron integrals typically used in SAPT. Then, using an already available Psi4NumpPy's helper module called helper_SAPT, all needed quantities were exported as NumPy arrays and became accessible in the main Python script. It is typical for expressions derived within the second quantization formalism to incorporate many tensor contractions, usually written using the Einstein summation convention. The already mentioned Numerical Python module -NumPy, contains a function einsum that enables the evaluation of expressions using the Einstein summation convention so that all tensor contractions can be written in a compact and readable manner.