In this chapter we will give an overview of the optical model description of nucleon-nucleus scattering and reactions based on fundamental nuclear two-body and many-body forces. We begin with a short overview followed by several commonly used theoretical techniques for deriving nucleon-nucleus optical model potentials that account for antisymmetry, Pauli blocking, and multiple scattering. We then summarize current efforts to derive microscopic nuclear forces consistent with the fundamental theory of strong interactions, quantum chromodynamics, and the use of such interactions in the construction of microscopic optical potentials. We also outline the dispersive optical potential approach, which despite being primarily phenomenological, has its origins in formal Green's function theory. Finally, we benchmark the results from modern optical potentials to experimental data.

We formulate a microscopic optical potential from chiral twoand three-body forces. The real and imaginary central terms of the optical potential are obtained from the nucleon self-energy in infinite matter, while the real spin-orbit term is extracted from a nuclear energy density functional constructed from the density matrix expansion using the same chiral potential. The density-dependent optical potential is then folded with the nuclear density distributions for selected Calcium isotopes resulting in energy-dependent nucleon-nucleus optical potentials from which we study proton-nucleus elastic scattering cross sections calculated using the TALYS reaction code. We compare the results of the microscopic calculations to phenomenological models and experimental data.