Hybrid density-functional theory beyond old limits

Hybrid density-functional theory (DFT) has long been the foundation of choice for accurate quantum-chemical simulations, but simulation size restrictions in periodic implementations have kept the vast majority of simulations in materials science restricted to semilocal functionals. This talk describes a drastically enhanced implementation of hybrid density functional theory in the FHI-aims code [1], applicable to thousands of atoms without any special precision restrictions and demonstrated for periodic system sizes above 10,000 atoms. The FHI-aims code enables precise yet efficient molecular (non-periodic) and materials (periodic) simulations including all electrons through well-tested, highly reliable numeric atom-centered basis sets, avoiding the need for shape approximations to the wave functions or potentials. The combination of hybrid DFT with high-accuracy dispersion methods facilitates highly accurate, direct simulations of large, complex organic-inorganic hybrid materials or molecular crystals. As one specific example, the talk considers hybrid organic-inorganic perovskites, particularly prospects for doping or alloying in large supercell calculations, as well as spin properties of their energy bands. Another example is the use of hybrid DFT as a means to quantify the uncertainty of predicted energy levels in complex inorganic semiconductors with qualitatively different constituents (here, Eu in multinary chalcogenides), leading to the disccovery of a previously unsynthesized semiconductor Cu₂EuSnSe₄ with an experimentally verified, promising band gap for photovoltaics.

This work would not be possible without the very large FHI-aims community (https://fhi-aims.org) and a very large group of excellent colleagues and collaborators over many years.