Dr. Nenad Vukmirović from the Institute of Physics Belgrade and his research group are dedicated to understanding charge transport in semiconducting materials - an essential process underlying the performance of all electronic devices. "To improve these devices", he explains, "it is absolutely necessary to perform simulations of these materials". Given the complexity of such simulations, the group relies heavily on high-performance computing (HPC) resources. "We need high-performance computing resources to perform these simulations as fast as possible", Nenad emphasizes.
The group investigates three broad classes of materials, each requiring a tailored simulation strategy. The first are disordered organic materials, in which electronic states are localized and charge moves by hopping between sites. "For these materials, we use methods that are capable of performing electronic structure calculations for systems containing on the order of ten thousand atoms", says Nenad. These large-scale simulations are followed by multi-scale modeling to bridge length scales from a few nanometers to about 100 nanometers, enabling the prediction of macroscopic transport properties such as temperature-dependent mobility.
The second class includes conventional crystalline materials, like silicon. Here, simulations are grounded in density functional theory (DFT), which provides detailed insight into electronic states and lattice vibrations—phonons. "We calculate the coupling between electrons and phonons, which actually limits the charge transport in the material", he explains. These electron-phonon interactions must be computed on dense momentum-space grids, requiring highly specialized computational methods to ensure accuracy.
Finally, the group also explores materials with intermediate properties, where strong electron-phonon coupling may lead to the formation of polarons—quasiparticles composed of electrons coupled with phonons. "For these materials, we are going to develop methods that will be able to simulate the mobility of charge, which are polarons", Nenad notes. This research is conducted within the framework of PolMoReMa, a project funded by the Science Fund of the Republic of Serbia.
Across all these efforts, HPC remains indispensable. It enables the group to handle large, complex systems, perform advanced multi-scale modeling, and ensure that simulations faithfully capture the physical behavior of materials critical for future electronics.
