An approximate version of Hartree-Fock theory in which the more computationally expensive integrals are replaced by adjustable parameters, which are determined by fitting experimental atomic and molecular data. Different choices of parameterization lead to different specific theories (e.g., MNDO, AM1, PM3).

Method of computational chemistry using some empirical (real-world, from the lab) data to simplify the calculations necessary.

relying to some extent on observation or experiment