You are cordially invited to the seminar of the Scientific Computing Laboratory of the Center for the Study of Complex Systems and of the project Polaron Mobility in Model Systems and Real Materials (PolMoReMa). The seminar will be held on Thursday, 27 November 2025 at 14:00 in the library reading room "Dr Dragan Popović" of the Institute of Physics Belgrade. The talk entitled

QMC study of transport in Holstein polaron model

will be given by Suzana Miladić (Scientific Computing Laboratory, Institute of Physics Belgrade). The abstract of the talk:

Organic semiconductors are emerging materials that are shaping modern technologies (OLEDs, OFETs, OPVs). Their low cost, mechanical flexibility, and tunable properties make them highly promising for a wide range of applications. However, realizing their full potential requires a detailed understanding of charge transport in these materials.

In this work, we investigate transport within the Holstein polaron model—a simple yet representative framework for organic molecular semiconductors. We develop a path-integral Quantum Monte Carlo method for computing current–current correlation functions and the dc mobility in the 1D Holstein model [1]. By carefully choosing the basis for the trace expansion in path integral, we suppress the dynamical sign problem and are able to evaluate correlation functions over long real-time intervals with small errors.

Using the Kubo formula, we extract the dc mobility either through direct integration of real-time correlation functions or via analytic continuation that combines real- and imaginary-time data. This approach yields highly precise results for dc mobility across a broad parameter range. The numerically exact results obtained here provide a great benchmark for evaluating the validity of commonly used transport theories, which rely on approximations appropriate only in extreme cases (strong or weak electron–phonon coupling, very low or high temperature).

By comparing our numerical results to the predictions of each transport theory, we are able to map out the parameter ranges—defined by temperature, electron–phonon interaction strength, and phonon frequency—over which small-polaron hopping, polaron band transport, or conventional band transport offers an accurate description of charge transport. This allows us to construct a transport-regime diagram for the 1D Holstein model, offering better insights into its transport behavior [2].

This research is supported by the Science Fund of the Republic of Serbia, Grant No. 5468, Polaron Mobility in Model Systems and Real Materials – PolMoReMa.

[1] S. Miladić and N. Vukmirović, Phys. Rev. B 107, 184315 (2023).
[2] S. Miladić and N. Vukmirović, Phys. Rev. B 112, 054314 (2025).