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

Abstract

Phonons crucially impact a variety of properties of organic semiconductor materials. For instance, charge- and heat transport depend on low-frequency phonons, while for other properties, such as the free energy, especially high-frequency phonons count. For all these quantities one needs to know the entire phonon band structure, whose simulation becomes exceedingly expensive for more complex systems when using methods like dispersion-corrected density functional theory (DFT). Therefore, in the present contribution we evaluate the performance of more approximate methodologies, including density functional tight binding (DFTB) and a pool of force fields (FF) of varying complexity and sophistication. Beyond merely comparing phonon band structures, we also critically evaluate to what extent derived quantities, like temperature-dependent heat capacities, mean squared thermal displacements and temperature-dependent free energies are impacted by shortcomings in the description of the phonon bands. As a benchmark system, we choose (deuterated) naphthalene, as the only organic semiconductor material for which to date experimental phonon band structures are available in the literature. Overall, the best performance amongst the approximate methodologies is observed for a system-specifically parametrized second-generation force field. Interestingly, in the low-frequency regime also force fields with a rather simplistic model for the bonding interactions (like the General Amber Force Field) perform rather well. As far as the tested DFTB parametrization is concerned, we obtain a significant underestimation of the unit cell volume resulting in a pronounced overestimation of the phonon energies in the low frequency region. This cannot be mended by relying on the DFT-calculated unit cell, since with this unit cell the DFTB phonon frequencies significantly underestimate the experiments.

Supporting Information is available free of charge at https://pubs.acs.org/doi/abs/10.1021/acs.jctc.0c00119

References in corpus (7)

• Phonons and related properties of extended systems from density-functional perturbation theory
• Long-range correlation energy calculated from coupled atomic response functions
• The transient localization scenario for charge transport in crystalline organic materials
• Chasing the killer phonon mode for the rational design of low disorder, high mobility molecular semiconductors
• Microscopic origin of entropy-driven polymorphism in hybrid organic-inorganic perovskite materials
• Lattice thermal expansion and anisotropic displacements in urea, bromomalonic aldehyde, pentachloropyridine and naphthalene
• Simulation of Charge Transport in Organic Semiconductors: A Time-Dependent Multiscale Method Based on Non-Equilibrium Green's Functions

Cited by in corpus (4)

• Machine learned Force-Fields for an ab-initio Quality Description of Metal-Organic Frameworks
• Identifying the Bottleneck for Heat Transport in Metal-Organic Frameworks
• Electron-phonon coupling and mobility modeling in organic semiconductors: method and application to tetracene polymorphs
• Manning-type potential induced by kink scatterings with phonons in molecular chains with hyperbolic double-well substrates