Directional bonds for ellipsoids. A new style for coarse-grained molecular modelling

The MOLC model is a coarse-grained (CG) force field initially developed to describe organic semiconductors. This force field uses finite-size aspherical particles connected with directional bonds. The particles are decorated with virtual sites representing point charges. Short-range interactions are accounted for with the generalised Gay-Berne potential, while electrostatic and long-range interactions are accounted for with a modified version of the usual Coulomb pairwise summation and reciprocal-space Ewald solver, respectively. The MOLC model is parametrised from the bottom-up and offers a general framework for describing soft materials with a structural accuracy comparable to that of atomic force fields. A 1-to-1 mapping procedure allows the reverse-mapping of CG to atomic coordinates, which are suitable to carry out electronic-structure calculations, thus capturing the complexity of real materials. The general characteristics, advantages and trade-offs of the model are presented, along with a selection of case studies in organic electronics.