ABINIT is a package whose main program allows one to find the total energy, charge density, electronic structure and many other properties of systems made of electrons and nuclei, (molecules and periodic solids) within Density Functional Theory (DFT), Many-Body Perturbation Theory (GW approximation and Bethe-Salpeter equation) and Dynmical Mean Field Theory (DMFT). ABINIT also allows to optimize the geometry according to the DFT forces and stresses, to perform molecular dynamics simulations using these forces, and to generate dynamical matrices, Born effective charges and dielectric tensors. The present paper aims to describe the new capabilities of ABINIT that have been developed since 2009. It covers both physical and technical developments inside the ABINIT code, as well as developments provided within the ABINIT package. The developments are described with relevant references, input variables, tests and tutorials.

Isodensity representation of the hole and the electron in the excitonic state of CH3NH3PbI3 showing spatial separation of the polaronic charges.

We carry out first-principles calculations of band gaps of cubic inorganic perovskites belonging to the class CsBX, with B = Pb, Sn and X = Cl, Br, I. We use the quasi-particle self-consistent GW method with efficient vertex corrections to calculate the electronic structure of the studied materials. We demonstrate the importance of including the higher-lying core and semicore shells among the valence states. For a meaningful comparison with experimental values, we account for thermal vibrations and disorder through ab initio molecular dynamics. Additionally, we calculate the spin-orbit coupling at levels of theory of increasing accuracy and show that semilocal density functionals significantly underestimate these corrections. We show that all of these effects need to be properly included in order to obtain reliable predictions for the band gaps of halide perovskites.

Note: This article is part of the JCP Special Topic on Electronic Structure Software.

We present a theoretical formulation for studying the pH-dependent interfacial coverage of semiconductor-water interfaces through ab initio electronic structure calculations, molecular dynamics simulations, and the thermodynamic integration method. This general methodology allows one to calculate the acidity of the individual adsorption sites on the surface and consequently the pH at the point of zero charge, pH, and the preferential adsorption mode of water molecules, either molecular or dissociative, at the semiconductor-water interface. The proposed method is applied to study the BiVO(010)-water interface, yields a pH in excellent agreement with the experimental characterization. Furthermore, from the calculated p K values of the individual adsorption sites, we construct an ab initio concentration diagram of all adsorbed species at the interface as a function of the pH of the aqueous solution. The diagram clearly illustrates the pH-dependent coverage of the surface and indicates that protons are found to be significantly adsorbed (∼1% of available sites) only in highly acidic conditions. The surface is found to be mostly covered by molecularly adsorbed water molecules in a wide interval of pH values ranging from 2 to 8. Hydroxyl ions are identified as the dominant adsorbed species at pH larger than 8.2.

We study hole and electron polarons in BiVO4 at finite temperature through hybrid functional molecular dynamics simulations. Through the thermodynamic integration method, we obtain the transition levels corresponding to the localized charges at 300 K. We observe that the polaron levels achieved in this way lie significantly closer to each other than those at 0 K. We find both hole and electron levels to lie within the band gap, with binding energies of 0.11 and 0.88 eV, respectively. Our calculations show that polaron localization significantly affects the alignment at the solid/liquid interface and that electron–hole recombination through polaronic states competes with the evolution of the water-splitting reaction in BiVO4.

We determine the energy levels of hole and electron polarons at the BiVO 4-water interface through hybrid functional molecular dynamics and thermodynamic integration, thereby accounting for the liquid nature of the water component. The electron polaron is found to be less stable at the interface than in the bulk by 0.18 eV, while for the hole polaron the binding energy increases by 0.20 eV when the charge localizes in the surface layer of BiVO 4. These results indicate that interfacial effects on the polaron binding energy and charge distribution are sizeable and cannot trivially be inferred from bulk calculations.

Perovskite photovoltaics advance rapidly, but questions remain regarding point defects: while experiments have detected the presence of electrically active defects no experimentally confirmed microscopic identifications have been reported. Here we identify lead monovacancy (VPb) defects in MAPbI3 (MA = CH3NH3+) using positron annihilation lifetime spectroscopy with the aid of density functional theory. Experiments on thin film and single crystal samples all exhibited dominant positron trapping to lead vacancy defects, and a minimum defect density of ~3 × 1015 cm−3 was determined. There was also evidence of trapping at the vacancy complex $$({{{{{\rm{V}}}}}}_{{{{{\rm{Pb}}}}}}{{{{{\rm{V}}}}}}_{{{{{\rm{I}}}}}})^{-}$$ ( V Pb V I ) − in a minority of samples, but no trapping to MA-ion vacancies was observed. Our experimental results support the predictions of other first-principles studies that deep level, hole trapping, $${{{{{{\rm{V}}}}}}}_{{{{{{\rm{Pb}}}}}}}^{2-}$$ V Pb 2 − , point defects are one of the most stable defects in MAPbI3. This direct detection and identification of a deep level native defect in a halide perovskite, at technologically relevant concentrations, will enable further investigation of defect driven mechanisms.