Interlayer Force Field for the Anisotropic Interaction between Planar Organic Molecules and Two-Dimensional Hexagonal Boron Nitride

We introduce a new interlayer potential (ILP) for simulating the adsorption and diffusion of planar organic molecules with partially charged heteroatoms on hexagonal boron nitride (hBN). Unlike previous models, this ILP incorporates all-atom electrostatic interactions alongside short-range repulsion and long-range attraction, enabling the accurate treatment of polar molecules. Parametrized against density functional theory data for pentacene and PTCDI, the ILP demonstrates transferability to related systems such as PTCDA. Comparative studies of nonpolar pentacene and polar PTCDA reveal distinct behaviors in single-molecule diffusion, cluster formation, and monolayer growth. PTCDA exhibits stronger binding due to electrostatic contributions, limiting diffusion to short-ranged hops, while pentacene undergoes long-range translocations facilitated by out-of-plane motions. At low coverage, PTCDA molecules lock into place via carbonyl-mediated hydrogen bonds, enabling only collective motion, whereas pentacene remains mobile. Monolayer simulations reproduce experimentally observed epitaxial morphologies: PTCDA forms a dense square lattice, while pentacene aligns parallel along its long axis. This ILP offers a computationally efficient and accurate alternative to ab initio and machine-learning methods, opening avenues for modeling polar organic molecules on hBN. Its utility extends to understanding layer formation and structural properties in hBN-encapsulated or -supported organic systems.