Solid state physics is the study of how atoms arrange themselves into solids and what properties these solids have. By examining the arrangement of the atoms and considering how electrons move among the atoms, it is possible to understand many macroscopic properties of materials such as their elasticity, electrical conductivity, or optical properties. The Institute of Solid State Physics focuses on organic, molecular, and nanostructured materials. Often detailed studies of the behavior of these materials at surfaces are made. Our research provides the foundation for important advances in technology such as energy efficient lighting, solar cells, electronic books, environmental sensors, and medical sensors.

Metastable Polymorphs

Doping molecular wires

Paper Strength

Computational Material Science

Solid State Seminar - Summer 2025
Wednesday 11 June 2025      

Modeling heat transport in organic semiconductors using non-equilibrium molecular dynamics
Florian Unterkofler

Abstract: Non-equilibrium molecular dynamics (NEMD) simulations are widely used to calculate the thermal conductivity of complex materials. They provide atomistic insights into heat transport processes in real space and offer a complementary perspective to lattice dynamics approaches, which operate in reciprocal space.
However, as there are numerous adjustable parameters and different variants, there is no universally agreed on best practice for implementing NEMD simulations that is established in literature. Therefore, we have developed a NEMD framework that has already yielded promising results for metal-organic frameworks (MOFs) [1] and crystalline polymers [2]. Still, important questions remain: Can this framework be further improved, and how do specific choices for certain parameters influence the results?
To address this, I revisited the established NEMD simulation framework and systematically evaluated several modifications aimed at improving the computational efficiency and also the accuracy of the calculated thermal conductivity values. The improved protocol is applied to the series of acene molecules systematically increasing their length and complexity. This serves as a testbed for benchmarking. The simulation results are validated against available experimental data and lattice dynamics calculations, demonstrating both the accuracy and robustness of the refined approach.
This puts us into an ideal position to perform simulations that not only deliver thermal conductivity values with increased accuracy, but also support advanced analysis approaches, which allow, for example, the identification of heat transport bottlenecks and structure–to-property relationships in organic semiconducting materials.

[1] Sandro Wieser and Egbert Zojer. "Machine learned force-fields for an Ab-initio quality description of metal-organic frameworks." npj Computational Materials 10.1 (2024): 18.
[2] Lukas Reicht, et al. "Analyzing Heat Transport in Crystalline Polymers in Real and Reciprocal Space." arXiv preprint arXiv:2503.14289 (2025).