Optimized Exchange and Correlation Semilocal Functional for the Calculation of Energies of Formation

We present a semiempirical exchange-correlation functional for density functional theory tailored to calculate energies of formation of solids. It has the same form of a Perdew–Burke–Ernzerhof functional, but three parameters have been fitted to reproduce experimental energies of formation of a representative set of binaries. The quality of the obtained functional has then been assessed for a control set of binary and ternary compounds. Our functional succeeds in reducing the error of the Perdew–Burke–Ernzerhof generalized gradient approximation for energies of formation by a factor of 2. Furthermore, this result is achieved preserving the quality of the optimized geometry

Optimized Exchange and Correlation Semilocal Functional for the Calculation of Energies of Formation

We present a semiempirical exchange-correlation functional for density functional theory tailored to calculate energies of formation of solids. It has the same form of a Perdew–Burke–Ernzerhof functional, but three parameters have been fitted to reproduce experimental energies of formation of a representative set of binaries. The quality of the obtained functional has then been assessed for a control set of binary and ternary compounds. Our functional succeeds in reducing the error of the Perdew–Burke–Ernzerhof generalized gradient approximation for energies of formation by a factor of 2. Furthermore, this result is achieved preserving the quality of the optimized geometry

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

Prediction and Synthesis of a Non-Zintl Silicon Clathrate

We use computational high-throughput techniques to study the thermodynamic stability of ternary type I Si clathrates. Two strategies to stabilize the structures are investigated: through endohedral doping of the 2<i>a</i> and 6<i>d</i> Wyckoff positions (located at the center of the small and large cages, respectively) and by substituting the Si 6<i>c</i> positions. Our results agree with the overwhelming majority of experimental results and predict a series of unknown clathrate phases. Many of the stable phases can be explained by the simple Zintl–Klemm rule, but some are unexpected. We then successfully synthesize one of the latter compounds, a new type I silicon clathrate containing Ba (inside the cages) and Be (in the 6<i>c</i> position). These results prove the predictive power and reliability of our strategy and motivate the use of high-throughput screening of materials properties for the accelerated discovery of new clathrate phases