Different mathematical approximations and formulations exist across physics and chemistry for calculating dipole-dipole interactions, depending on whether treating point dipoles, finite charge distributions, macroscopic media, or specific quantum/classical frameworks, making this a matter of basic scientific definition.
The claim refers to the existence of different mathematical formulae for calculating dipole-dipole interaction energy, which is standard foundational knowledge in physics and physical chemistry (e.g., point-dipole approximation versus finite-charge representations, orientation-averaged vs. instantaneous expressions, macroscopic effective medium theories). Because this is a matter of definitional and observational consensus in the physical sciences, no specific paper citation is necessary.