Globular proteins are roughly spherical biomolecules with attractive and highly directional interactions. This microscopic observation motivates describing these proteins as patchy particles: hard spheres with attractive surface patches. Mapping a biomolecule to a patchy model requires simplifying effective protein-protein interactions which in turn provides a microscopic understanding of the protein solution behavior. The patchy model can indeed be fully analyzed including its phase diagram. In this chapter we detail the methodology of mapping a given protein to a patchy model and of determining the phase diagram of the latter. We also briefly describe the theory upon which the methodology is based provide practical information and discuss potential pitfalls.
