Computing the Lattice Thermal Conductivity of Small-Molecule Organic Semiconductors: A Systematic Comparison of Molecular Dynamics Based Methods

While the Green-Kubo and non-equilibrium molecular dynamics methods have been compared quite extensively to calculate the thermal conductivity in inorganic compounds, there is currently a lack of comparison of these algorithms with the more recently developed approach-to-equilibrium molecular dynamics (AEMD) method for other types of materials such as organic semiconductors. To fill this gap, this article reports a theoretical description of thermal transport in single crystals made of terthiophene as prototypical system based on the three most popular molecular dynamics approaches. A systematic comparison of the computed values of thermal conductivity and its anisotropy is carried out and the strengths and weaknesses associated with each method are discussed. Although the three algorithms give essentially the same trends, this study points to the "AEMD" approach as the most suitable compromise between accuracy and computing cost. On the material aspects, the theoretical modeling yields an anisotropic character of the thermal transport in crystals whose out-of-plane thermal conductivity component is approximately twice larger than the in-plane components. The AEMD approach is further used to investigate the influence of temperature on thermal transport in terthiophene. The trends are utterly rationalized by relying on the concepts of phonon mean free paths and phonon group velocities.