Structure and Optical Properties of Small (TiO₂)_<i>n</i> Nanoparticles, <i>n</i> = 21–24

Recently, nanostructured TiO₂ (“black TiO₂”) has been discovered to absorb visible light, which makes it an efficient material for water splitting. Hydrogenization has been proposed to be at the origin of this beneficial electronic structure of black TiO₂. Here, we investigate, using ab initio methods, alternative mechanisms related to structure modifications in nanoclusters that could be responsible for absorption in the visible range. To that end, we apply a combination of computational structure prediction using simulated annealing and minima-hopping methods based on density-functional theory to predict low-energy configurations and time-dependent density-functional theory (TDDFT) using a hybrid functional with optimized Hartree–Fock content to obtain optical absorption edges

Prediction of Stable Nitride Perovskites

Perovskites are one of the most studied classes of materials, with a variety of applications in diverse fields of science and technology. Their basic composition is ABX₃, where X is a nonmetal normally from the VIA or VIIA group. In this article we investigate the possibility of the existence of perovskites with X<i> = </i>N. Our approach is based on a combination of high-throughput techniques and global structural prediction methods. We find 21 new compositions of the form ABN₃ that are thermodynamically stable (considering all possible decomposition channels) and that have therefore excellent chances of being experimentally accessible. Most of these materials crystallize in monoclinic phases, but three compounds, namely, LaReN₃, LaWN₃, and YReN₃, are predicted to have distorted perovskite structures in their ground state. In particular, LaWN₃ is a semiconductor and displays a large ferroelectric polarization. The addition of nitride compounds to the perovskite family poses numerous questions related to the chemistry of this interesting family of materials

Correction to Prediction of Stable Nitride Perovskites

Correction to Prediction of Stable Nitride Perovskite

Benchmark Many-Body <i>GW</i> and Bethe–Salpeter Calculations for Small Transition Metal Molecules

We study the electronic and optical properties of 39 small molecules containing transition metal atoms and 7 others related to quantum-dots for photovoltaics. We explore in particular the merits of the many-body <i>GW</i> formalism, as compared to the ΔSCF approach within density functional theory, in the description of the ionization energy and electronic affinity. Mean average errors of 0.2–0.3 eV with respect to experiment are found when using the PBE0 functional for ΔSCF and as a starting point for <i>GW</i>. The effect of partial self-consistency at the <i>GW</i> level is explored. Further, for optical excitations, the Bethe–Salpeter formalism is found to offer similar accuracy as time-dependent DFT-based methods with the hybrid PBE0 functional, with mean average discrepancies of about 0.3 and 0.2 eV, respectively, as compared to available experimental data. Our calculations validate the accuracy of the parameter-free <i>GW</i> and Bethe–Salpeter formalisms for this class of systems, opening the way to the study of large clusters containing transition metal atoms of interest for photovoltaic applications