Speaker
Description
The Diagrammatic Monte Carlo (DiagMC) technique has historically been successfully employed to study both large (Fröhlich) and small (Holstein) polarons [1]. A key advantage of DiagMC is its non-perturbative, all-coupling nature, which enables accurate treatment across the entire interaction regime, in contrast to perturbative and variational approaches that are typically limited to weak- and strong-coupling limits, respectively.
However, the Fröhlich and Holstein Hamiltonians are based on simplified assumptions---namely, a single isotropic electron band with quadratic dispersion and a single optical phonon mode with simplified electron--phonon coupling---which are often too restrictive to capture the complex electronic and vibrational structures of real materials. Extending DiagMC to realistic systems therefore requires overcoming these limitations. In this context, recent developments have introduced fully first-principles DiagMC frameworks [2], marking a significant step forward.
Here, we present DiagMC simulations of large polarons in real materials by relaxing key assumptions of the original models. Using first-principles-based formulations [3,4], we compute energy renormalization, polaron effective masses, dispersion relations, and quasiparticle weights for a range of materials, including AlAs, BaO, CaO, LiF, and TiO$_2$. We further benchmark our DiagMC results against existing studies based on perturbative and Feynman variational approaches [2,3,4], demonstrating consistency and highlighting the predictive power of the method.
References:
[1] AS Mishchenko et al. “Diagrammatic quantum Monte Carlo study of the Fröhlich polaron”. In: Physical Review B 62.10 (2000), p. 6317.
[2] Yao Luo, Jinsoo Park, and Marco Bernardi. “First-principles diagrammatic Monte Carlo for electron–phonon interactions and polaron”. In: Nature Physics 21.8 (2025), pp. 1275–1282.
[3] Bogdan Guster et al. “Fröhlich polaron effective mass and localization length in cubic materials: Degenerate and anisotropic electronic bands”. In: Physical Review B 104.23 (2021), p. 235123.
[4] Anna Miglio et al. “Predominance of non-adiabatic effects in zero-point renormalization of the electronic band gap”. In: npj Computational Materials 6.1 (2020), p. 167.