Evaluating Computational Shortcuts in Supercell-Based Phonon Calculations of Molecular Crystals: The Instructive Case of Naphthalene

Over the past decades molecular crystals have been studied extensively - especially in terms of electronic structure - to improve their performance in organic semiconductor-based devices. Many of the properties relevant in this context are crucially affected by phonons. For example, electron-phonon coupling is often found to be one of the main limiting factors for charge transport, or entropic contributions from phonons play a decisive role when it comes to reliably predicting phase stability of polymorphs close in energy. Despite their importance, measurements and ab initio simulations are often methodologically impeded in such complex systems. Thus, approximate simulation approaches are typically employed: density-functional based tight binding (DFTB) or classical force fields (FFs). Here, we quantitatively studied the errors one must expect when resorting to such methods for various phonon-related properties in crystalline naphthalene¹. Besides off-the-shelf solutions using publicly available parameters for DFTB or widely used FFs such as COMPASS and GAFF, we also critically test the performance of our own parametrization of the MOF-FF² for naphthalene.

¹ J. Chem. Theory Comput. 2020, 16, 4, 2716–2735
² Phys. Status Solidi B 2013, 250, 1128– 1141