First-Principles Linear Combination of Atomic Orbitals Calculations of KSiF Crystal: Structural, Electronic, Elastic, Vibrational and Dielectric Properties.

The results of first-principles calculations of the structural, electronic, elastic, vibrational, dielectric and optical properties, as well as the Raman and infrared (IR) spectra, of potassium hexafluorosilicate (KSiF; KSF) crystal are discussed. KSF doped with manganese atoms (KSF:Mn) is known for its ability to function as a phosphor in white LED applications due to the efficient red emission from Mn⁴⁺ activator ions. The simulations were performed using the CRYSTAL23 computer code within the linear combination of atomic orbitals (LCAO) approximation of the density functional theory (DFT).

Effect of Rh Doping on Optical Absorption and Oxygen Evolution Reaction Activity on BaTiO (001) Surfaces.

In the present work, we investigate the potential of modified barium titanate (BaTiO), an inexpensive perovskite oxide derived from earth-abundant precursors, for developing efficient water oxidation electrocatalysts using first-principles calculations. Based on our calculations, Rh doping is a way of making BaTiO absorb more light and have less overpotential needed for water to oxidize. It has been shown that a TiO-terminated BaTiO (001) surface is more promising from the point of view of its use as a catalyst.

Modeling of the Lattice Dynamics in Strontium Titanate Films of Various Thicknesses: Raman Scattering Studies.

While the bulk strontium titanate (STO) crystal characteristics are relatively well known, ultrathin perovskites' nanostructure, chemical composition, and crystallinity are quite complex and challenging to understand in detail. In our study, the DFT methods were used for modelling the Raman spectra of the STO bulk (space group I4/mcm) and 5-21-layer thin films (layer group p4/mbm) in tetragonal phase with different thicknesses ranging from ~0.8 to 3.

Water Splitting on Multifaceted SrTiO Nanocrystals: Calculations of Raman Vibrational Spectrum.

Various photocatalysts are being currently studied with the aim of increasing the photocatalytic efficiency of water splitting for production of hydrogen as a fuel and oxygen as a medical gas. A noticeable increase of hydrogen production was found recently experimentally on the anisotropic faces (facets) of strontium titanate (SrTiO, STO) nanoparticles. In order to identify optimal sites for water splitting, the first principles calculations of the Raman vibrational spectrum of the bulk and stepped (facet) surface of a thin STO film with adsorbed water derivatives were performed.

Oxygen Vacancy Formation and Migration within the Antiphase Boundaries in Lanthanum Scandate-Based Oxides: Computational Study.

The atomic structure of antiphase boundaries in Sr-doped lanthanum scandate (LaSrScO) perovskite, promising as the proton conductor, was modelled by means of DFT method. Two structural types of interfaces formed by structural octahedral coupling were constructed: edge- and face-shared. The energetic stability of these two interfaces was investigated.

BaCoO monoclinic structure and chemical bonding analysis: hybrid DFT calculations.

Cobalt based perovskites have great potential for numerous applications. Contrary to a generally assumed hexagonal space group (SG P6/mmc) model as the ground state of BaCoO (BCO), our hybrid DFT calculations with B1WC density functional and the symmetry group-subgroup derived crystal structure model support the ground state of BCO to be indeed monoclinic, in agreement with recent experimental predictions [Chin et al., Phys.

First principles calculations of the vibrational properties of single and dimer F-type centers in corundum crystals.

The present paper investigates the F-type centers in α-AlO through their electronic and vibrational properties from first principle calculations using a periodic supercell approach, a hybrid functional, and all-electron Gaussian basis sets as implemented in the CRYSTAL17 code. Single F-type and dimer F-type centers related to oxygen vacancies in various charge states were considered. The defect-induced vibrational modes were identified and found to appear mainly in the low (up to 300 cm) and high (above 700 cm) frequency regions, depending on the defect charge.

Hybrid density functional theoretical study of NASICON-type NaTi(PO) (x = 1-4).

Sodium Super Ionic Conductor (NASICON) structured phosphate framework compounds represent a very attractive class of materials for their use as Na-ion battery electrodes. A series of NASICON-structured NaTi(PO) compounds corresponding to varying degrees of sodiation (x = 1-4) have been investigated using high-level hybrid density functional theory calculations using the Linear Combination of Atomic Orbitals and Gaussian-type basis set formalism together with hybrid B1WC and HSE06 exchange-correlation functionals. Using primitive cells of NaTi(PO) compounds with different stoichiometry, sodium sublattice structure and titanium oxidation states are constructed and analyzed using group theoretical symmetry considerations.

Interface-induced enhancement of piezoelectricity in the (SrTiO)/(BaTiO) superlattice for energy harvesting applications.

We present the results of a detailed first principles study of the piezoelectric properties of the (SrTiO)/(BaTiO) heterostructure using the 3D STO/BTO superlattice model. The atomic basis set, hybrid functionals and slabs with different numbers of STO and BTO layers were used. The interplay between ferroelectric (FE) and antiferrodistortive (AFD) displacements is carefully analyzed.

Manifestation of dipole-induced disorder in self-assembly of ferroelectric and ferromagnetic nanocubes.

The colloidal processing of nearly monodisperse and highly crystalline single-domain ferroelectric or ferromagnetic nanocubes is a promising route to produce superlattice structures for integration into next-generation devices, whereas controlling the local behaviour of nanocrystals is imperative for fabricating highly-ordered assemblies. The current picture of nanoscale polarization in individual nanocrystals suggests a potential presence of a significant dipolar interaction, but its role in the condensation of nanocubes is unknown. We simulate the self-assembly of colloidal dipolar nanocubes under osmotic compression and perform the microstructural characterization of their densified ensembles.

First-principles calculations of iodine-related point defects in CsPbI.

We present here first principles hybrid functional calculations of the atomic and electronic structure of several iodine-related point defects in CsPbI, a material relevant for photovoltaic applications. We show that the presence of neutral interstitial I atoms or electron holes leads to the formation of di-halide dumbbells of I (analogous to the well-known situation in alkali halides). Their formation and one-electron energies in the band gap are determined.

Thermodynamic stability of non-stoichiometric SrFeO: a hybrid DFT study.

SrFeO3-δ is a mixed ionic-electronic conductor with a complex magnetic structure that reveals a colossal magnetoresistance effect. This material and its solid solutions are attractive for various spintronic, catalytic and electrochemical applications, including cathodes for solid oxide fuel cells and permeation membranes. Its properties strongly depend on oxygen non-stoichiometry.

Anomalous Kinetics of Diffusion-Controlled Defect Annealing in Irradiated Ionic Solids.

The annealing kinetics of the primary electronic F-type color centers (oxygen vacancies with trapped one or two electrons) is analyzed for three ionic materials (AlO, MgO, and MgF) exposed to intensive irradiation by electrons, neutrons, and heavy swift ions. Phenomenological theory of diffusion-controlled recombination of the F-type centers with much more mobile interstitial ions (complementary hole centers) allows us to extract from experimental data the migration energy of interstitials and pre-exponential factor of diffusion. The obtained migration energies are compared with available first-principles calculations.

Electromechanical Properties of BaSrTiO Perovskite Solid Solutions from First-Principles Calculations.

An enhancement of the piezoelectric properties of lead-free materials, which allow conversion of mechanical energy into electricity, is a task of great importance and interest. Results of first-principles calculations of piezoelectric/electromechanical properties of the BaSrTiO (BSTO) ferroelectric solid solution with a perovskite structure are presented and discussed. Calculations are performed within the linear combination of atomic orbitals (LCAO) approximation and periodic-boundary conditions, using the advanced hybrid functionals of density functional theory (DFT).

First-principles calculations of oxygen interstitials in corundum: a site symmetry approach.

Using site symmetry analysis, four possible positions of interstitial oxygen atoms in the α-AlO hexagonal structure have been identified and studied. First principles hybrid functional calculations of the relevant atomic and electronic structures for interstitial O atom insertion in these positions reveal differences in energies of ∼1.5 eV.

Thermodynamic stability of stoichiometric LaFeO and BiFeO: a hybrid DFT study.

BiFeO perovskite attracts great attention due to its multiferroic properties and potential use as a parent material for BiSrFeO and BiSrFeCoO solid solutions in intermediate temperature cathodes of oxide fuel cells. Another iron-based LaFeO perovskite is the end member for well-known solid solutions (LaSrFeCoO) used for oxide fuel cells and other electrochemical devices. In this study an ab initio hybrid functional approach was used for the study of the thermodynamic stability of both LaFeO and BiFeO with respect to decompositions to binary oxides and to elements, as a function of temperature and oxygen pressure.

First principles study of confinement effects for oxygen vacancies in BaZrO₃ (001) ultra-thin films.

In this contribution, we study possible confinement effects on the atomic and electronic structure, and phonon properties of neutral (V(O)(x) and fully charged (V(O)oxygen vacancies in BaZrO3 (001) ultra-thin films. First principles phonon calculations were performed as a function of film thickness (from 3 to 7 atomic planes) with two complementary DFT methods. The calculations reveal that for both types of vacancies the confinement effect is very short-range; for films containing 5 planes or more, the oxygen vacancy properties are predicted to be similar to those observed in the bulk material.

Ab Initio Thermodynamics of Oxygen Vacancies and Zinc Interstitials in ZnO.

ZnO is an important wide band gap semiconductor with potential application in various optoelectronic devices. In the current contribution, we explore the thermodynamics of oxygen vacancies and zinc interstitials in ZnO from first-principles phonon calculations. Formation enthalpies are evaluated using hybrid DFT calculations, and phonons are addressed using the PBE and the PBE+U functionals.

Thermodynamic properties of neutral and charged oxygen vacancies in BaZrO3 based on first principles phonon calculations.

The structural, electronic and thermodynamic properties of neutral and positively doubly charged oxygen vacancies in BaZrO3 are addressed by first principles phonon calculations. The calculations are performed using two complementary first principles approaches and functionals; the linear combination of atomic orbitals (LCAO) within the hybrid Hartree-Fock and density functional theory formalism (HF-DFT), and the projector augmented plane wave approach (PAW) within DFT. Phonons are shown to contribute significantly to the formation energy of the charged oxygen vacancy at high temperatures (∼1 eV at 1000 K), due to both its large distortion of the local structure, and its large negative formation volume.

Formation and migration of oxygen vacancies in La(1-x)Sr(x)Co(1-y)Fe(y)O(3-δ) perovskites: insight from ab initio calculations and comparison with Ba(1-x)Sr(x)Co(1-y)Fe(y)O(3-δ).

The formation and migration of oxygen vacancies in the series of (La,Sr)(Co,Fe)O(3-δ) perovskites, which can be used as mixed conducting SOFC cathode materials and oxygen permeation membranes, are explored in detail by means of first principles density functional calculations. Structure distortions, charge redistributions and transition state energies during the oxygen ion migration are obtained and analyzed. Both the overall chemical composition and vacancy formation energy are found to have only a small impact on the migration barrier; it is rather the local cation configuration which affects the barrier.

The first-principles treatment of the electron-correlation and spin-orbital effects in uranium mononitride nuclear fuels.

The DFT+U calculations were employed in a detailed study of the strong electron correlation effects in a promising nuclear fuel-uranium mononitride (UN). A simple method for solving the multiple minima problem in DFT+U simulations and insure obtaining the correct ground state is suggested and applied. The crucial role of spin-orbit interactions in reproduction of the U atom total magnetic moment is demonstrated.

Ab initio DFT+U study of He atom incorporation into UO(2) crystals.

We present and discuss results of the density functional theory (DFT) for perfect UO(2) crystals with He atoms in octahedral interstitial positions therein. We have calculated basic bulk crystal properties and He incorporation energies into the low temperature anti-ferromagnetic UO(2) phase using several exchange-correlation functionals within the spin-polarized local density (LDA) and generalized gradient (GGA) approximations. In all DFT calculations we included the on-site correlation corrections using the Hubbard model (DFT+U approach).

Adsorption of atomic and molecular oxygen on the LaMnO3(001) surface: ab initio supercell calculations and thermodynamics.

We present and discuss the results of ab initio DFT plane-wave supercell calculations of the atomic and molecular oxygen adsorption and diffusion on the LaMnO(3) (001) surface which serves as a model material for a cathode of solid oxide fuel cells. The dissociative adsorption of O(2) molecules from the gas phase is energetically favorable on surface Mn ions even on a defect-free surface. The surface migration energy for adsorbed O ions is found to be quite high, 2.

Evidence for interfacial-storage anomaly in nanocomposites for lithium batteries from first-principles simulations.

We present theoretical support for a mass storage anomaly proposed for nanocomposites in the context of lithium batteries which forms the transition between an electrostatic capacitive mechanism and an electrode mechanism. Ab initio atomic and electronic structure calculations, performed on the Ti(0001)/Li2O(111) model interface, indicate the validity of the phenomenological model of interfacial Li storage and provide a deeper insight into the local situation. Beyond the specific applicability to storage devices, the possibility of a two-phase effect on mass storage generally highlights the availability of novel degrees of freedom in materials research when dealing with nanocomposites.