Computational insights on dynamic disorder in molecular crystals – from electron structure over phonons to thermodynamics

Abstract

Quantum-chemical nature of molecular interactions and atomic vibrations imparts a ubiquitous internal dynamics even to solid molecular materials that appear as very rigid from the macroscopic point of view. Existence of flat potential energy basins related to dynamic degrees of freedom in molecular crystals usually gives birth to large-amplitude motions of molecular segments or entire molecules that is commonly recognized as dynamic disorder. Computational chemistry offers suitable approaches for sampling these potential energy surfaces, subsequently enabling to model atomic displacements related to disorder and contributions of this internal dynamics to macroscopic material properties such as entropy, volatility, solubility, plasticity or conductivity. This highlight article presents a mosaic of recent research results which were achieved thanks to the computational methods playing a perfectly complementary role to experimental approaches. Observed material properties and the either beneficial or detrimental impact of dynamic disorder thereon can be then interpreted at the atomic level which naturally contributes to a better understanding of the underlying phenomena and enables to rationalize future material design. This highlight article illustrates the impact of dynamic disorder in the fields of barocaloric materials for heat management, active pharmaceutical ingredients and organic molecular semiconductors. Such a scope enables to account for how the dynamic disorder manifests itself in modelling thermodynamic or spectroscopic properties, phase behavior, electron structure and charge transport in molecular crystals.