Marios Zacharias

Density functional tight-binding (DFTB), a semi-empirical approach rooted in density functional theory, is well-suited for simulating large periodic systems. Following Jiang et al. [Phys. Rev. Mater. 9, 023803 (2025)], we have specifically tailored DFTB parameters for accurate electronic bandgap calculations in both three-dimensional and two-dimensional lead bromide perovskites, significantly reducing computational costs compared to conventional ab initio methods. Our electronic DFTB parameters provide reliable predictions for key electronic properties, such as bandgaps and effective masses, closely matching existing experimental data and advanced many body perturbation theory calculations. Furthermore, our approach successfully captures the bandgap trends observed in mixed-halide perovskites, reflecting the variation with halide composition. In addition, we explore the transferability of the newly optimized DFTB parameters to predict the electronic properties of a variety of low-dimensional perovskites and related structures with edge- or face-sharing octahedra.

A new rhombohedral LaH₄ phase is predicted to be a high-T_c superconductor with a critical temperature above 100 K at 25 GPa.

Relying on the anharmonic special displacement method, we introduce an ab initio quasistatic polymorphous framework to describe local disorder, anharmonicity, and electron-phonon coupling in superionic conductors. Using cubic Cu_{2}Se, we show that positional polymorphism yields the breakdown of the phonon quasiparticle picture, leading to extremely overdamped anharmonic vibrations while preserving transverse acoustic phonons, consistent with experiments. We also demonstrate highly broadened electronic spectral functions with band gap openings of 1.0 eV due to polymorphism, and that anharmonic electron-phonon coupling leads to a band gap narrowing with increasing temperature. Our approach, relying on generating a handful of configurations, opens the way for efficient calculations in superionic crystals to elucidate their compelling high figure of merit.

Realizing semiconductors with high symmetry of their crystallographic structures has been a virtue of inorganic materials and has resulted in novel physical behaviors. In contrast, hybrid (organic and inorganic) crystals such as two-dimensional metal halide perovskites exhibit much lower crystal symmetry due to in-plane or out-of-plane octahedral distortions. Despite their amazing ability for photoinduced light emission at room temperature, the Achilles' heel of this attractive class of 2D materials for optoelectronics remains the poor control and lack of performance for charge carrier transport. Inspired by the tremendous charge carrier properties of the 3D cubic perovskite phase (α) of FAPbI₃ and combining the use of the appropriate cage cation, the spacer molecule and the temperature and rate of crystallization, we report a new series of FA-based layered two-dimensional perovskites that exhibits the highest theoretically predicted symmetry with a tetragonal P4/mmm space group, resulting in no octahedral distortion in both in-plane and out-of-plane directions. These 2D perovskites present the shortest interlayer distances (4 Å), which results in systematically lower bandgaps (1.7 to 1.8 eV). Finally, the absence of octahedral distortions, results in an exciton diffusion length of 2.5 µm, and a diffusivity of 4.4 cm2s-1, both of which are an order of magnitude larger compared to previously reported 2D perovskites and on par with monolayer transition metal dichalcogenides.