Advances in computational studies of energy materials

A theoretical perspective on solid-state ionic interfaces

Solid-state ionic conductors find application across various domains in materials science, particularly showcasing their significance in energy storage and conversion technologies. To effectively utilize these materials in high-performance electrochemical devices, a comprehensive understanding and precise control of charge carriers' distribution and ionic mobility at interfaces are paramount. A major challenge lies in unravelling the atomic-level processes governing ion dynamics within intricate solid and interfacial structures, such as grain boundaries and heterophases. From a theoretical viewpoint, in this Perspective article, my focus is to offer an overview of the current comprehension of key aspects related to solid-state ionic interfaces, with a particular emphasis on solid electrolytes for batteries, while providing a personal critical assessment of recent research advancements. I begin by introducing fundamental concepts for understanding solid-state conductors, such as the classical diffusion model and chemical potential. Subsequently, I delve into the modelling of space-charge regions, which are pivotal for understanding the physicochemical origins of charge redistribution at electrified interfaces. Finally, I discuss modern computational methods, such as density functional theory and machine-learned potentials, which offer invaluable tools for gaining insights into the atomic-scale behaviour of solid-state ionic interfaces, including both ionic mobility and interfacial reactivity aspects. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'.

A Single Model for the Thermodynamics and Kinetics of Metal Exsolution from Perovskite Oxides

Exsolution has emerged as an outstanding route for producing oxide-supported metal nanoparticles. For ABO3-perovskite oxides, various late transition-metal cations can be substituted into the lattice under oxidizing conditions and exsolved as metal nanoparticles after reduction. A consistent and comprehensive description of the point-defect thermodynamics and kinetics of this phenomenon is lacking, however. Herein, supported by hybrid density-functional-theory calculations, we propose a single model that explains diverse experimental observations, such as why substituent transition-metal cations (but not host cations) exsolve from perovskite oxides upon reduction; why different substituent transition-metal cations exsolve under different conditions; why the metal nanoparticles are embedded in the surface; why exsolution occurs surprisingly rapidly at relatively low temperatures; and why the reincorporation of exsolved species involves far longer times and much higher temperatures. Our model's foundation is that the substituent transition-metal cations are reduced to neutral species within the perovskite lattice as the Fermi level is shifted upward within the bandgap upon sample reduction. The calculations also indicate unconventional influences of oxygen vacancies and A-site vacancies. Our model thus provides a fundamental basis for improving existing, and creating new, exsolution-generated catalysts.

Comparison of the different distribution functions in Gd-doped ceria system by molecular dynamics simulations

Cerium dioxide-based materials are among the most studied for applications in the energy and environmental fields and are also of interest in biology and medicine. The fluorite structure of CeO₂is locally distorted by the concomitant presence of doping cations, such as Gd³⁺and oxygen vacancies. The cation-anion bond length distribution then becomes increasingly asymmetric with the doping ratio and temperature. In these cases, the MD simulation results indicate that the commonly used maximum of the pair correlation functiong(r) first peak can no longer be adopted to estimate the mean bond length. To determine the true cation-anion bond length, the analysis of the radial distribution functionR(r) first peak is necessary. Furthermore, the asymmetry of this peak must be accounted for when extracting the mean value of the distribution. The gap between theg(r) maximum and theR(r) mean position derived from the fit using a skewed Gaussian function clearly increases with the doping ratio and temperature, leading to different conclusions concerning bond length evolution. The present study also suggests that care must be taken when the bond length is deduced from the pair distribution functionsG^pdf(r) as is the case in total scattering experiments (x-ray and neutrons). Finally, relations between the cumulants of the effective distribution of distances as determined in extended x-ray absorption fine structure experiments and the cumulants describing the real distance distribution are proposed considering that both these distributions are modelled by a skewed Gaussian function.

Cation binding of Li(I), Na(I) and Zn(II) to cobalt and iron sulphide clusters - electronic structure study

The binding of alkaline (Li⁺ and Na⁺) and zinc (Zn²⁺) cations to mononuclear disulphides MS₂ and to persulphides, containing an S-S bond, M(S₂), to binuclear disulphides M₂S₂ and persulphides M₂(S₂) and to cubic tetranuclear sulphides M₄S₄ where M = Fe, Co, is examined by density functional theory with the B3LYP functional, and dispersion corrections were applied. For the small-sized clusters (up to two transition metal centres), the energy gaps between different configurations were verified by CCSD(T) calculations. Persulphides M(S₂) are more stable than disulphides MS₂ as bare clusters, upon carbonyl and chloride ligand coordination and upon cation binding (Li⁺, Na⁺, Zn²⁺). The one-electron reduction of alkali cations and two-electron reduction of Zn²⁺ reverses order of stability and the planar disulphides (MS₂-reduced cation) become more stable; the energy gap disulphide to persulphide increases. In all reduced clusters, zinc ions form bonds with sulphur and with the transition metal centre (Co or Fe). Lithium cations also form bonds to cobalt or iron, but only in the M₂S₂ clusters, upon reduction. Energy barriers were calculated for the disulphide to persulphide reaction in the Zn-Co-S₂ system in the isolated clusters (gas-phase), in water, acetonitrile and 1-Cl-hexane solution. Most significant decrease in the energy barriers were obtained with less-polar solvents, acetonitrile, and particularly, 1-Cl-hexane. In M₄S₄ clusters, the cations do not reach optimal coordination to the sulphur centres. The global minima of M₂S₂ clusters are antiferromagnetic; in the reduced Zn-M₂S₂ clusters, magnetic moment is induced at zinc centres as a result of charge transfer between Zn and Co or Zn and Fe.

Excited States Calculations of MoS2@ZnO and WS2@ZnO Two-Dimensional Nanocomposites for Water-Splitting Applications

Transition metal dichalcogenide (TMD) MoS2 and WS2 monolayers (MLs) deposited atop of crystalline zinc oxide (ZnO) and graphene-like ZnO (g-ZnO) substrates have been investigated by means of density functional theory (DFT) using PBE and GLLBSC exchange-correlation functionals. In this work, the electronic structure and optical properties of studied hybrid nanomaterials are described in view of the influence of ZnO substrates thickness on the MoS2@ZnO and WS2@ZnO two-dimensional (2D) nanocomposites. The thicker ZnO substrate not only triggers the decrease of the imaginary part of dielectric function relatively to more thinner g-ZnO but also results in the less accumulated charge density in the vicinity of the Mo and W atoms at the conduction band minimum. Based on the results of our calculations, we predict that MoS2 and WS2 monolayers placed at g-ZnO substrate yield essential enhancement of the photoabsorption in the visible region of solar spectra and, thus, can be used as a promising catalyst for photo-driven water splitting applications.

Time-Dependent Density Functional Theory Calculations of N- and S-Doped TiO2 Nanotube for Water-Splitting Applications

On the basis of time-dependent density functional theory (TD-DFT) we performed first-principle calculations to predict optical properties and transition states of pristine, N- and S-doped, and N+S-codoped anatase TiO2 nanotubes of 1 nm-diameter. The host O atoms of the pristine TiO2 nanotube were substituted by N and S atoms to evaluate the influence of dopants on the photocatalytic properties of hollow titania nanostructures. The charge transition mechanism promoted by dopants positioned in the nanotube wall clearly demonstrates the constructive and destructive contributions to photoabsorption by means of calculated transition contribution maps. Based on the results of our calculations, we predict an increased visible-light-driven photoresponse in N- and S-doped and the N+S-codoped TiO2 nanotubes, enhancing the efficiency of hydrogen production in water-splitting applications.

Advances in Theoretical Calculation of Halide Perovskites for Photocatalysis

Photocatalysis, which includes water splitting for hydrogen fuel generation, degradation of organic pollutants, and CO2 reduction using renewable solar energy, is one of the most promising solutions for environmental protection and energy conversion. Halide perovskite has recently emerged as a new promising material for photocatalytic applications. The exploration of new efficient halide perovskite-based photocatalysts and understanding of photocatalytic reaction mechanisms can be revealed using theoretical calculations. The progress and applications of first-principles atomistic modeling and simulation of halide perovskite photocatalysts, including metal halide perovskites, halide perovskite heterojunctions, and other promising perovskite derivatives, are presented in this review. Critical insights into the challenges and future research directions of photocatalysis using halide perovskites are also discussed.

Theoretical insights of codoping to modulate electronic structure of [Formula: see text] and [Formula: see text] for enhanced photocatalytic efficiency

[Formula: see text] and [Formula: see text] are well known materials in the field of photocatalysis due to their exceptional electronic structure, high chemical stability, non-toxicity and low cost. However, owing to the wide band gap, these can be utilized only in the UV region. Thus, it's necessary to expand their optical response in visible region by reducing their band gap through doping with metals, nonmetals or the combination of different elements, while retaining intact the photocatalytic efficiency. We report here, the codoping of a metal and a nonmetal in anatase [Formula: see text] and [Formula: see text] for efficient photocatalytic water splitting using hybrid density functional theory and ab initio atomistic thermodynamics. The latter ensures to capture the environmental effect to understand thermodynamic stability of the charged defects at a realistic condition. We have observed that the charged defects are stable in addition to neutral defects in anatase [Formula: see text] and the codopants act as donor as well as acceptor depending on the nature of doping (p-type or n-type). However, the most stable codopants in [Formula: see text] mostly act as donor. Our results reveal that despite the response in visible light region, the codoping in [Formula: see text] and [Formula: see text] cannot always enhance the photocatalytic activity due to either the formation of recombination centers or the large shift in the conduction band minimum or valence band maximum. Amongst various metal-nonmetal combinations, [Formula: see text] (i.e. Mn is substituted at Ti site and S is substituted at O site), [Formula: see text] in anatase [Formula: see text] and [Formula: see text], [Formula: see text] in [Formula: see text] are the most potent candidates to enhance the photocatalytic efficiency of anatase [Formula: see text] and [Formula: see text] under visible light irradiation.

Pressure-Induced Phase Transitions in Sesquioxides

Pressure is an important thermodynamic parameter, allowing the increase of matter density by reducing interatomic distances that result in a change of interatomic interactions. In this context, the long range in which pressure can be changed (over six orders of magnitude with respect to room pressure) may induce structural changes at a much larger extent than those found by changing temperature or chemical composition. In this article, we review the pressure-induced phase transitions of most sesquioxides, i.e., A2O3 compounds. Sesquioxides constitute a big subfamily of ABO3 compounds, due to their large diversity of chemical compositions. They are very important for Earth and Materials Sciences, thanks to their presence in our planet’s crust and mantle, and their wide variety of technological applications. Recent discoveries, hot spots, controversial questions, and future directions of research are highlighted.

Adsorption of Water onto SrTiO3 from Periodic Møller-Plesset Second-Order Perturbation Theory

Adsorption of water onto metal oxide surfaces is a long-standing problem motivated by relevance to many promising technological applications. In this work, we compute the adsorption energy of water on SrTiO₃ using periodic Møller-Plesset second-order perturbation theory (MP2). We compare our MP2 results to density functional and hybrid density functional theory calculations with and without the widely used D3 dispersion correction. The MP2 ground-state adsorption energy of water on SrTiO₃ (001) at one monolayer coverage is 0.9 eV on the TiO₂ termination in the molecular configuration and 0.6 eV in the dissociative configuration, the corresponding results on the SrO termination being 0.9 eV for both modes of adsorption. These results are reproduced well by the PBE and PBE0 exchange-correlation functionals. Correcting for dispersion effects through the D3 dispersion correction leads to significantly overestimated adsorption energies for both PBE and PBE0 with respect to MP2. The D3 correction also fails to capture the difference in electron correlation between the molecular and dissociative adsorption states, similarly to the optB86b van der Waals density functional.

Perspective: Theory and simulation of hybrid halide perovskites

Organic-inorganic halide perovskites present a number of challenges for first-principles atomistic materials modeling. Such "plastic crystals" feature dynamic processes across multiple length and time scales. These include the following: (i) transport of slow ions and fast electrons; (ii) highly anharmonic lattice dynamics with short phonon lifetimes; (iii) local symmetry breaking of the average crystallographic space group; (iv) strong relativistic (spin-orbit coupling) effects on the electronic band structure; and (v) thermodynamic metastability and rapid chemical breakdown. These issues, which affect the operation of solar cells, are outlined in this perspective. We also discuss general guidelines for performing quantitative and predictive simulations of these materials, which are relevant to metal-organic frameworks and other hybrid semiconducting, dielectric and ferroelectric compounds.

The interface of SrTiO3 and H2O from density functional theory molecular dynamics

We use dispersion-corrected density functional theory molecular dynamics simulations to predict the ionic, electronic and vibrational properties of the SrTiO₃/H₂O solid-liquid interface. Approximately 50% of surface oxygens on the planar SrO termination are hydroxylated at all studied levels of water coverage, the corresponding number being 15% for the planar TiO₂ termination and 5% on the stepped TiO₂-terminated surface. The lateral ordering of the hydration structure is largely controlled by covalent-like surface cation to H₂O bonding and surface corrugation. We find a featureless electronic density of states in and around the band gap energy region at the solid-liquid interface. The vibrational spectrum indicates redshifting of the O-H stretching band due to surface-to-liquid hydrogen bonding and blueshifting due to high-frequency stretching vibrations of OH fragments within the liquid, as well as strong suppression of the OH stretching band on the stepped surface. We find highly varying rates of proton transfer above different SrTiO₃ surfaces, owing to differences in hydrogen bond strength and the degree of dissociation of incident water. Trends in proton dynamics and the mode of H₂O adsorption among studied surfaces can be explained by the differential ionicity of the Ti-O and Sr-O bonds in the SrTiO₃ crystal.

State-of-the-art Sn2+-based ternary oxides as photocatalysts for water splitting: electronic structures and optoelectronic properties

Synthesis and electronic structures for Sn²⁺-based oxide materials are reviewed in an attempt to develop visible-light-responsive photocatalysts.

Determination of the nitrogen vacancy as a shallow compensating center in GaN doped with divalent metals

We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p-type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

Energetic stability and photocatalytic activity of SrTiO3 nanowires: ab initio simulations

Ab initio simulations have been performed to describe, for the first time, energetic stability and photocatalytic activity of SrTiO₃ nanowires.

CO2 conversion to methanol on Cu(i) oxide nanolayers and clusters: an electronic structure insight into the reaction mechanism

The CO₂ hydrogenation to methanol using dissociated water as the hydrogen source proceeds via stable carboxyl, formic acid and formaldehyde intermediates.

Transferable Force Field for Metal-Organic Frameworks from First-Principles: BTW-FF

We present an ab-initio derived force field to describe the structural and mechanical properties of metal-organic frameworks (or coordination polymers). The aim is a transferable interatomic potential that can be applied to MOFs regardless of metal or ligand identity. The initial parametrization set includes MOF-5, IRMOF-10, IRMOF-14, UiO-66, UiO-67, and HKUST-1. The force field describes the periodic crystal and considers effective atomic charges based on topological analysis of the Bloch states of the extended materials. Transferable potentials were developed for the four organic ligands comprising the test set and for the associated Cu, Zn, and Zr metal nodes. The predicted materials properties, including bulk moduli and vibrational frequencies, are in agreement with explicit density functional theory calculations. The modal heat capacity and lattice thermal expansion are also predicted.

Prediction of electron energies in metal oxides

The ability to predict energy levels in metal oxides is paramount to developinguseful materials, such as in the development of water photolysis catalysts and efficient photovoltaic cells. The binding energy of electrons in materials encompasses a wealth of information concerning their physicochemistry. The energies control the optical and electrical properties, dictating for which kinds of chemistry and physics a particular material is useful. Scientists have developed theories and models for electron energies in a variety of chemical systems over the past century. However, the prediction of quantitative energy levels in new materials remains a major challenge. This issue is of particular importance in metal oxide research, where novel chemistries have opened the possibility of a wide range of tailored systems with applications in important fields including light-emitting diodes, energy efficient glasses, and solar cells. In this Account, we discuss the application of atomistic modeling techniques, covering the spectrum from classical to quantum descriptions, to explore the alignment of electron energies between materials. We present a number of paradigmatic examples, including a series of oxides (ZnO, In2O3, and Cu2O). Such calculations allow the determination of a "band alignment diagram" between different materials and can facilitate the prediction of the optimal chemical composition of an oxide for use in a given application. Throughout this Account, we consider direct computational solutions in the context of heuristic models, which are used to relate the fundamental theory to experimental observations. We review a number of techniques that have been commonly applied in the study of electron energies in solids. These models have arisen from different answers to the same basic question, coming from solid-state chemistry and physics perspectives. We highlight common factors, as well as providing a critical appraisal of the strengths and weaknesses of each, emphasizing the difficulties in translating concepts from molecular to solid-state systems. Finally, we stress the need for a universal description of the alignment of band energies for materials design from first-principles. By demonstrating the applicability and challenges of using theory to calculate the relevant quantities, as well as impressing the necessity of a clarification and unification of the descriptions, we hope to provide a stimulus for the continued development of this field.

Lithium and sodium battery cathode materials: computational insights into voltage, diffusion and nanostructural properties

Energy storage technologies are critical in addressing the global challenge of clean sustainable energy. Major advances in rechargeable batteries for portable electronics, electric vehicles and large-scale grid storage will depend on the discovery and exploitation of new high performance materials, which requires a greater fundamental understanding of their properties on the atomic and nanoscopic scales. This review describes some of the exciting progress being made in this area through use of computer simulation techniques, focusing primarily on positive electrode (cathode) materials for lithium-ion batteries, but also including a timely overview of the growing area of new cathode materials for sodium-ion batteries. In general, two main types of technique have been employed, namely electronic structure methods based on density functional theory, and atomistic potentials-based methods. A major theme of much computational work has been the significant synergy with experimental studies. The scope of contemporary work is highlighted by studies of a broad range of topical materials encompassing layered, spinel and polyanionic framework compounds such as LiCoO2, LiMn2O4 and LiFePO4 respectively. Fundamental features important to cathode performance are examined, including voltage trends, ion diffusion paths and dimensionalities, intrinsic defect chemistry, and surface properties of nanostructures.

Band alignment of rutile and anatase TiO₂

The most widely used oxide for photocatalytic applications owing to its low cost and high activity is TiO₂. The discovery of the photolysis of water on the surface of TiO₂ in 1972 launched four decades of intensive research into the underlying chemical and physical processes involved. Despite much collected evidence, a thoroughly convincing explanation of why mixed-phase samples of anatase and rutile outperform the individual polymorphs has remained elusive. One long-standing controversy is the energetic alignment of the band edges of the rutile and anatase polymorphs of TiO₂ (ref. ). We demonstrate, through a combination of state-of-the-art materials simulation techniques and X-ray photoemission experiments, that a type-II, staggered, band alignment of ~ 0.4 eV exists between anatase and rutile with anatase possessing the higher electron affinity, or work function. Our results help to explain the robust separation of photoexcited charge carriers between the two phases and highlight a route to improved photocatalysts.

Molecular dynamics simulations of oxygen vacancy diffusion in SrTiO3

A classical force-field model with partial ionic charges was applied to study the behaviour of oxygen vacancies in the perovskite oxide strontium titanate (SrTiO(3)). The dynamical behaviour of these point defects was investigated as a function of temperature and defect concentration by means of molecular dynamics (MD) simulations. The interaction between oxygen vacancies and an extended defect, here a Σ3(111) grain boundary, was also examined by means of MD simulations. Analysis of the vacancy distribution revealed considerable accumulation of vacancies in the envelope of the grain boundary. The possible clustering of oxygen vacancies in bulk SrTiO(3) was studied by means of static lattice calculations within the Mott-Littleton approach. All binary vacancy-vacancy configurations were found to be energetically unfavourable.

Routes to copper zinc tin sulfide Cu2ZnSnS4 a potential material for solar cells

Power generation through photovoltaics (PV) has been growing at an average rate of 40% per year over the last decade; but has largely been fuelled by conventional Si-based technologies. Such cells involve expensive processing and many alternatives use either toxic, less-abundant and or expensive elements. Kesterite Cu(2)ZnSnS(4) (CZTS) has been identified as a solar energy material composed of both less toxic and more available elements. Power conversion efficiencies of 8.4% (vacuum processing) and 10.1% (non-vacuum processing) from cells constructed using CZTS have been achieved to date. In this article, we review various deposition methods for CZTS thin films and the synthesis of CZTS nanoparticles. Studies of direct relevance to solar cell applications are emphasised and characteristic properties are collated.

Holes bound as small polarons to acceptor defects in oxide materials: why are their thermal ionization energies so high?

Holes bound to acceptor defects in oxide materials usually need comparatively high energies, of the order of 0.5-1.0 eV, to be ionized thermally to the valence band maximum. It is discussed that this has to be attributed to the stabilization of such holes by mainly short range interactions with the surrounding lattice, leading to the formation of small O(-) polarons. This is tantamount to the localization of the hole at only one of several equivalent oxygen ions next to the defect. The hole stabilizing energies can be determined experimentally from the related intense optical absorption bands. This paper exploits previous phenomenological studies of bound-hole small polarons in order to account for the large hole stabilization energies on this basis. A compilation demonstrates that bound-hole small polarons occur rather often in oxides and also in some related materials. The identification of such systems is based on EPR and optical studies and also on recent advanced electronic structure calculations.

Multi-component transparent conducting oxides: progress in materials modelling

Transparent conducting oxides (TCOs) play an essential role in modern optoelectronic devices through their combination of electrical conductivity and optical transparency. We review recent progress in our understanding of multi-component TCOs formed from solid solutions of ZnO, In(2)O(3), Ga(2)O(3) and Al(2)O(3), with a particular emphasis on the contributions of materials modelling, primarily based on density functional theory. In particular, we highlight three major results from our work: (i) the fundamental principles governing the crystal structures of multi-component oxide structures including (In(2)O(3))(ZnO)(n) and (In(2)O(3))(m)(Ga(2)O(3))(l)(ZnO)(n); (ii) the relationship between elemental composition and optical and electrical behaviour, including valence band alignments; (iii) the high performance of amorphous oxide semiconductors. On the basis of these advances, the challenge of the rational design of novel electroceramic materials is discussed.

Electron and hole stability in GaN and ZnO

We assess the thermodynamic doping limits of GaN and ZnO on the basis of point defect calculations performed using the embedded cluster approach and employing a hybrid non-local density functional for the quantum mechanical region. Within this approach we have calculated a staggered (type-II) valence band alignment between the two materials, with the N 2p states contributing to the lower ionization potential of GaN. With respect to the stability of free electron and hole carriers, redox reactions resulting in charge compensation by ionic defects are found to be largely endothermic (unfavourable) for electrons and exothermic (favourable) for holes, which is consistent with the efficacy of electron conduction in these materials. Approaches for overcoming these fundamental thermodynamic limits are discussed.

Towards sustainable photovoltaics: the search for new materials

The opportunities for photovoltaic (PV) solar energy conversion are reviewed in the context of projected world energy demands for the twenty-first century. Conventional single-crystal silicon solar cells are facing increasingly strong competition from thin-film solar cells based primarily on polycrystalline absorber materials, such as cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS). However, if PVs are to make a significant contribution to satisfy global energy requirements, issues of sustainability and cost will need to be addressed with increased urgency. There is a clear need to expand the range of materials and processes that is available for thin-film solar cell manufacture, placing particular emphasis on low-energy processing and sustainable non-toxic raw materials. The potential of new materials is exemplified by copper zinc tin sulphide, which is emerging as a viable alternative to the more toxic CdTe and the more expensive CIGS absorber materials.

Uncovering the complex behavior of hydrogen in Cu2O

The behavior of hydrogen in p-type Cu(2)O has been reported to be quite unusual. Muon experiments have been unable to ascertain the preferential hydrogen site within the Cu(2)O lattice, and indicate that hydrogen causes an electrically active level near the middle of the band gap, whose nature, whether accepting or donating, is not known. In this Letter, we use screened hybrid-density-functional theory to study the nature of hydrogen in Cu(2)O, and identify for the first time the "quasiatomic" site adopted by hydrogen in Cu(2)O. We show that hydrogen will always act as a hole killer in p-type Cu(2)O, and is one likely cause of the low performance of Cu(2)O solar cell devices.

Atomistic and electronic structure of (X 2 O 3 ) n nanoclusters; n =1–5, X=B, Al, Ga, In and Tl

The stable and metastable, as measured using an all-electron density functional theory approach, stoichiometric clusters of boron, aluminium, gallium, indium and thallium oxide are reported. Initial candidate structures were found using an evolutionary algorithm to search the energy landscape, defined using classical interatomic potentials, for alumina and india followed by data mining or rescaling. Characterization of the refined structures was performed by electronic structure techniques at the hybrid density functional and many-body GW levels of theory. We make accurate predictions of the spectroscopic properties represented by mean ionization potentials of 11.4, 9.9, 9.8, 8.8 and 8.4 eV and electron affinities of 0.05, 1.1, 1.6, 1.9 and 2.5 eV for boria, alumina, gallia, india and thallia, respectively. The changes in the global minima, atomistic and electronic properties with respect to the cluster and cation size are discussed.

Reevaluation of the structure and fundamental physical properties of dawsonites by DFT studies

Dawsonite-type compounds, with the general formula MAlCO(3)(OH)(2), where M = Na(+), K(+), or NH(4)(+), recently have become attractive materials because of their potential interest in geochemical CO(2) sequestration, CO(2) capture in power plants, and heterogeneous catalysis. However, the number of studies assessing the properties of these materials is limited. In the present paper, we report a theoretical reevaluation of the structural and essential physicochemical properties of Na-, K-, and NH(4)-dawsonites as determined by density functional theory (DFT) investigations. The calculated structure of Na- and K-dawsonites is in good agreement with previous data, while for NH(4)AlCO(3)(OH)(2), the calculations suggest orientation disorder of the ammonium ions in the structure. The normal-mode analysis, electronic and bonding properties, and elastic properties are reported for the three analogue dawsonites. The calculated formation enthalpy is -1714, -1699, and -1655 kJ/mol for K-, Na-, and NH(4)-dawsonite, respectively. This study comprises a first step toward a better understanding of the diversity of dawsonite intrinsic properties, which is required to tune their practical applications.

Effects of reduced dimensionality on the electronic structure and defect chemistry of semiconducting hybrid organic–inorganic PbS solids

The combination of inorganic and organic frameworks to produce crystalline hybrid semiconductors offers a pathway for obtaining novel photovoltaic and optoelectronic materials. Taking an archetypal binary semiconductor, PbS (galena), we investigate the electronic effects of the reduced dimensionality in the PbS framework on transition from bulk PbS to three-dimensional and one-dimensional hybrid inorganic–organic networks. Analysis of density functional theory calculations reveals the substantial contribution of the organic (benzenehexathiol derivates) to the band-edge states. Implications for intrinsic defect formation and potential application in solar cell devices are discussed, as well as future design pathways for engineering the electronic properties of this new class of hybrid metal–organic framework.