Projector Augmented Wave Research Articles

Quantum chemical modeling of the structure and stability of hydrated and sulfated stannic acid complexes

Various H2SnO3 complexes and their hydrated and sulfated derivatives are calculated within the framework of the cluster approximation with the B3LYP, ωB97XD DFT functionals and the LanL2DZ(Sn), 6-31G**(O,S,H) and DGDZVP basis sets, and taking into account periodic boundary conditions with the PBE functional and the basis of the projector-augmented plane waves PAW. It was found that among the considered hydrated forms, the most energetically preferred are nanostructures in the form of ultrathin bars with a Sn2O2 cross section of the composition SnO2/1.5H2O and SnO2/2H2O. For sulfated complexes, two types of structures can be formed: with H2SO4 molecules adsorbed onto the surface of the hydrate shell around SnO2, and more stable structures with SO42− anions directly bound to Sn atoms on the surface of the tin oxide backbone.

Covariant Jacobi-Legendre expansion for total energy calculations within the projector augmented wave formalism

Covariant Jacobi-Legendre expansion for total energy calculations within the projector augmented wave formalism

A DFT study of the effect of hydrostatic pressure on the structure and electronic properties of sarcosine crystal

ContextWe perform density functional theory calculations to study the dependence of the structural and electronic properties of the amino acid sarcosine crystal structure on hydrostatic pressure application. The results are analyzed and compared with the available experimental data. Our findings indicate that the crystal structure and properties of sarcosine calculated using the Grimme dispersion-corrected PBE functional (PBE-D3) best agree with the available experimental results under hydrostatic pressure of up to 3.7 GPa. Critical structural rearrangements, such as unit cell compression, head-to-tail compression, and molecular rotations, are investigated and elucidated in the context of experimental findings. Band gap energy tuning and density of state shifts indicative of band dispersion are presented concerning the structural changes arising from the elevated pressure. The calculated properties indicate that sarcosine holds great promise for application in electronic devices that involve pressure-induced structural changes.MethodsThree widely used generalized gradient approximation functionals—PBE, PBEsol, and revPBE—are employed with Grimme’s D3 dispersion correction. The non-local van der Waals density functional vdW-DF is also evaluated. The calculations are performed using the projector-augmented wave method in the Quantum Espresso software suite. The geometry optimization results are visualized using VMD. The Multiwfn and NCIPlot programs are used for wavefunction and intermolecular interaction analyses.

DFT-based simulation for the semiconductor behavior of XGeCl3 (X=K, Rb) halide perovskites under hydrostatic pressure

In this work, the structural and electronic properties of XGeCl3 (X=K, Rb) crystallized in cubic cell (Pm-3m, 221) were presented under hydrostatic pressure from 0 to 8 GPa using the first-principal Density Functional Theory (DFT) under the Perdew–Burke–Ernzerhof (PBE) form of the generalized gradient approximation (GGA). The Projector Augmented Wave (PAW) method describing electron–ion interaction was used here. For XGeCl3 (X=K, Rb), the lattice constants were calculated as 5.171 and 5.197 Å, and the band gaps were predicted as 0.5802 and 0.657 eV, respectively at ambient pressure. It was observed that the lattice parameters and bond lengths of the XGeCl3 (X=K, Rb) compounds decreased with increased pressure. The applied hydrostatic pressure reduced the band gaps, and the metallic character was detected at 5 GPa for both structures. This study provides a theoretical basis that may have potential uses in optoelectronic applications of the XGeCl3 (X=K, Rb) perovskites.

Niobium Modification in Ni‐Rich Cathode Materials for Li‐Ion Batteries: Insights from Ab Initio Calculations

Herein, a theoretical study on Nb‐doped LiNiO2 cathode materials for Li‐ion batteries is performed based on density functional theory within the projector augmented wave method. Due to the stronger NbO interaction, the Ni‐rich cathode modified by Nb has better electronic conductivity, higher potential, and larger O‐vacancy formation energy. During the charging and discharging process, Nb doping can reduce the lattice distortion, which is conducive to improve the cycle performance of the electrode. This work provides a new insight into the atomic configuration and the origin of the performance enhancement for Nb‐doped LiNiO2 cathode and is a necessary complement to the experiment, thus helpful for rational design and manufacture of high‐performance Ni‐rich cathode materials.

Mechanistic investigation of methanol-to-olefins conversion catalyzed by H-ZSM-5 zeolite: a DFT study.

The mechanisms for the formation of the first C - C bond and lower olefins on methanol to olefins (MTO) conversion on H-ZSM-5 had been focused in dispute. In this paper, density functional theory has been used to study the reaction mechanisms of methanol to olefins on ZSM-5. The configurations of reactants, intermediates, products and transition state of the numerous reactions involved in such a process have been optimized, as well as the elementary reactions related to these configurations were determined by the calculation of corresponding activation energy barriers and reaction heats. Here, two different kinds of the mechanisms were proposed for the formation of dimethylether (DME), one involving an associative interaction of two methanol molecules with the zeolite Brønsted acid sites and the other occurring via a surface methoxy species and a methanol molecule. A critical intermediate of the methoxy methyl cation was theoretically verified by the reaction of the methoxy species and dimethylether. Besides, it was found that the first intermediates containing a C - C bond were 1,2-dimethoxyethane and 2-methoxy-ethanolare, in which the former was formed from methoxy species with dimethyl ether and the latter was formed from methanol by onium ions((CH3)2O+CH2CH2OCH3), respectively. For the whole reaction mechanism, the results in this paper indicated that the ethene formation is more favorable than propylene formation due to the low activation energy barrier for ethene formation (123.49 vs. 162.09kJ.mol-1). From these calculations, it would be concluded that ethene is the first alkene product that induces the occurrence of the hydrocarbon pool mechanism. All the periodic density function theory (DFT) calculations were performed by the Vienna Ab Initio Simulation package (VASP). The interaction between nucleus and valence electron was described using the pseudopotentials found in the projector augmented wave (PAW) method. PBE-D3 was used in the whole DFT calculations and CI-NEB was used to locate transition state.

Probing Short-Range Interactions in Isostructural Hydrate and Perhydrate of Dabrafenib by Magic-Angle Spinning Solid-State NMR.

Dabrafenib (DBF), an anticancer drug, exhibits isostructural properties in its hydrate (DBF⊃H2O) and perhydrate (DBF⊃H2O2) forms, as revealed by single-crystal X-ray diffraction. Despite the H2O and H2O2 solvent molecules occupying identical locations, the two polymorphs have different thermal behaviors. In general, determination of stoichiometry of H2O in the perhydrate crystals is difficult due to the presence of both H2O and H2O2 in the same crystal voids. This study utilizes magic-angle spinning (MAS) solid-state NMR (SSNMR) combined with gauge-included projector augmented wave calculations to characterize the influence of solvent molecules on the local environment in pseudopolymorphs. SSNMR experiments were employed to assign 1H, 13C, and 15N peaks and identify spectral differences in the isostructural pseudopolymorphs. Proton spectroscopy at fast MAS was used to identify and quantify H2O2/H2O in DBF⊃H2O2 (mixed hydrate/perhydrate). 1H-1H dipolar-coupling-based experiments were recruited to confirm the 3D molecular packing of solvent molecules in DBF⊃H2O and DBF⊃H2O2. Homonuclear (1H-1H) and heteronuclear (1H-14N) distance measurements, in conjunction with diffraction structures and optimized hydrogen atom positions by density functional theory, helped decipher local interactions of H2O2 with DBF and their geometry in DBF⊃H2O2. This integrated X-ray structure, quantum chemical calculations, and NMR study of pseudopolymorphs offer a practical approach to scrutinizing crystallized solvent interactions in the crystal lattice even without high-resolution crystal structures or artificial sample enrichment.

Pressure-Driven Responses in Cd2SiO4 and Hg2GeO4 Minerals: A Comparative Study

The structural, elastic, and electronic properties of orthorhombic Cd2SiO4 and Hg2GeO4 were examined under varying pressure conditions using first-principles calculations based on density functional theory employing the Projector Augmented Wave method. The obtained cell parameters at 0 GPa were found to align well with existing experimental data. We delved into the pressure dependence of normalized lattice parameters and elastic constants. In Cd2SiO4, all lattice constants decreased as pressure increased, whereas, in Hg2GeO4, parameters a and b decreased while parameter c increased under pressure. Employing the Hill average method, we calculated the elastic moduli and Poisson’s ratio up to 10 GPa, noting an increase with pressure. Evaluation of ductility/brittleness under pressure indicated both compounds remained ductile throughout. We also estimated elastic anisotropy and Debye temperature under varying pressures. Cd2SiO4 and Hg2GeO4 were identified as indirect band gap insulators, with estimated band gaps of 3.34 eV and 2.09 eV, respectively. Interestingly, Cd2SiO4 exhibited a significant increase in band gap with increasing pressure, whereas the band gap of Hg2GeO4 decreased under pressure, revealing distinct structural and electronic responses despite their similar structures.

Unveiling ductile, rare-earth-free structural materials: A DFT exploration of MnTi and MnZr

This paper presents a theoretical exploration of the electronic, structural, and mechanical attributes inherent in three rare-earth-free intermetallic compounds, namely, MnTi, MnZr, and MnHf. Employing density functional theory (DFT) calculations with the Implementation of projector augmented wave (PAW); our investigation adopts the supercell approach to meticulously determine the structural and mechanical properties of these materials. The findings reveal that MnTi and MnZr exhibit intrinsic ductility, positioning them as viable contenders for applications demanding high-strength structures. In contrast, MnHf demonstrates mechanical instability. This study provides promising insights into the mechanical characteristics of MnTi and MnZr, underscoring their potential as sustainable structural materials, given the abundance and non-toxic nature of their constituents. The research findings presented herein contribute to the understanding of rare-earth-free intermetallics, offering valuable information for applications in materials science and engineering.

Energy structure of mixed halide CeF2Cl and CeFCl2 crystals

The band energy structures of CeF2Cl and CeFCl2 crystals have been calculated using the projector augmented-wave (PAW) method and the hybrid exchange-correlation functional PBE0. The valence band top consists of 2p states of F and 3p states of Cl. An energy gap is observed between the 5d states of Ce in the bottom part of the conduction band of both crystals, forming two subbands, 5d1 and 5d2, with very different effective electron masses (2.49 m0 and 0.19 m0 for CeF2Cl and 5.95 m0 and 0.84 m0 for CeFCl2, respectively). The 4f states of Ce are placed within the forbidden band. The obtained values for the band gap of CeF2Cl and CeFCl2 crystals are 6 eV and 4.6 eV, respectively.

Unveiling the Electronic Structure of SnS for Photocatalytic Applications: A DFT Approach†

AbstractPhotocatalytic materials are of great scientific interest due to their potential applications in sustainable energy sources. Band gap and optical absorption of the materials are two core characteristics for photocatalysis that eventually depend on electronic structure. In order to accurately compute (predict) the electronic‐scale properties of a crystalline solid using first principles calculations, which might be costly to measure experimentally, large‐scale atomic level calculation frameworks have been made possible through the use of density functional theory (DFT). We have used DFT with many body perturbation theory (MBPT) by solving the bethe‐salpeter equation (BSE) to priorly predict the properties of bulk tin sulfide (SnS) as it meets the necessary requirements for photocatalytic applications. We fixed the DFT band gap underestimation by including the Hubbard parameter (U) and used projector augmented wave pseudo‐potentials with generalized‐gradient approximation (GGA) to calculate the electronic and optical properties of SnS. Optical properties were computed using independent particle approximation (IPA) and BSE with DFT+U wave functions. Our theoretical results align with experimental data for this material, demonstrating the potential for further research in validating experimental results with theoretical approximations and empirical relations.

GPAW: An open Python package for electronic structure calculations.

We review the GPAW open-source Python package for electronic structure calculations. GPAW is based on the projector-augmented wave method and can solve the self-consistent density functional theory (DFT) equations using three different wave-function representations, namely real-space grids, plane waves, and numerical atomic orbitals. The three representations are complementary and mutually independent and can be connected by transformations via the real-space grid. This multi-basis feature renders GPAW highly versatile and unique among similar codes. By virtue of its modular structure, the GPAW code constitutes an ideal platform for the implementation of new features and methodologies. Moreover, it is well integrated with the Atomic Simulation Environment (ASE), providing a flexible and dynamic user interface. In addition to ground-state DFT calculations, GPAW supports many-body GW band structures, optical excitations from the Bethe-Salpeter Equation, variational calculations of excited states in molecules and solids via direct optimization, and real-time propagation of the Kohn-Sham equations within time-dependent DFT. A range of more advanced methods to describe magnetic excitations and non-collinear magnetism in solids are also now available. In addition, GPAW can calculate non-linear optical tensors of solids, charged crystal point defects, and much more. Recently, support for graphics processing unit (GPU) acceleration has been achieved with minor modifications to the GPAW code thanks to the CuPy library. We end the review with an outlook, describing some future plans for GPAW.

Half-metallic ferromagnetism in double perovskites Pb2XX'O6 (X = V and Cr and X’ = Zr and Hf)

The structural, magnetic, and electronic properties of Pb-based double perovskite, Pb2XX'O6 (X = V and Cr and X’ = Zr and Hf), have been studied in this paper. This study uses the first-principal projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as considering the on-site Coulomb re-pulsive interaction (GGA+U). The structure of these Pb-based double perovskite is calculated with four magnetic states, antiferromagnetic (AFM), ferromagnetic (FM), ferrimagnetic (FiM), nonmagnetic (NM), and then we compare the energy of these states to find the most stable state. We quickly discovered that all these materials have a lower energy level at the ferromagnetic state, especially Pb2VZrO6 which has an energy difference between AFM and FM state of 120 meV. By analyzing the density of states (DOS) and its magnetic moment, we further discovered that all these materials are half-metallic ferromagnetic (HM-FM). They have an integer magnetic moment because all these materials have a band gap in the spin-down channel. Under GGA + U, the band gap still exists and enlarges, and the V series materials became more stable because of the larger differences between the state of AFM and FM, while the Cr series have the opposite. Lastly, we calculate the electron configuration of V, Cr, Zr, and Hf under GGA and GGA + U calculations in this paper. The HM characteristics of the band gap in one of its spin channels and its ferromagnetic nature mean that there are huge potential applications of these new compounds in spintronics.

Investigation of electronic, elastic, dynamical, thermodynamic and thermoelectric properties of Cobalt based half-Heusler compounds

Heusler compounds have attracted remarkable attention from scientists over the year by virtue of their peculiarity and suitability in multi-functional applications. In the current study, the structural, elastic, dynamical, thermodynamic and thermoelectric properties of CoMSb (M = V, Nb and Ta) half-Heusler compounds were computed. Projector augmented-wave (PAW) pseudopotentials with PBE exchange correlation functional have been used to obtain the results for the studied compounds. The computed elastic constants satisfy the general stability condition based on the cubic symmetry and endorse the ductile nature of the compounds. The CoVSb compound is predicted to be ferromagnetic half-metallic compound while CoNbSb and CoTaSb are non-magnetic compounds. The dynamical properties revealed the dynamical stability in CoVSb and CoTaSb compounds while the imaginary frequency observed at W⟶L⟶Γ predicts instability in CoNbSb compound. The thermodynamic properties for the compounds were reported. The thermoelectric properties were calculated based on the results obtained from electronic structure using semi-classical Boltzmann theory. The ductile nature and the figure of merit computed predict CoMSb (M = V, Nb and Ta) are relatively good for thermoelectric application.

Formic acid stability in different solvents by DFT calculations.

New technologies have been developed toward the use of green energies. The production of formic acid (FA) from carbon dioxide (CO[Formula: see text]) hydrogenation with H[Formula: see text] is a sustainable process for H[Formula: see text] storage. However, the FA adduct stabilization is thermodynamically dependent on the type of solvent and thermodynamic conditions. The results suggest a wide range of dielectric permittivity values between the dimethyl sulfoxide (DMSO) and water solvents to stabilize the FA in the absence of base. The thermodynamics analysis and the infrared and charge density difference results show that the formation of the FA complex with H[Formula: see text]O is temperature dependent and has a major influence on aqueous solvents compared to the FA adduct with amine, in good agreement with the experiment. In these conditions, the stability thermodynamic of the FA molecule may be favorable at non-organic solvents and dielectric permittivity values closer to water. Therefore, a mixture of aqueous solvents with possible ionic composition could be used to increase the thermodynamic stability of H[Formula: see text] storage in CO[Formula: see text] conversion processes. Using the Quantum ESPRESSO package, density functional theory (DFT) calculations were performed with periodic boundary conditions, and the electronic wave functions were expanded in plane waves. For the exchange-correlation functional, we use the vdW-DF functional with the inclusion of van der Waals (vdW) forces. Electron-ion interactions are treated by the projector augmented wave (PAW) method with pseudopotentials available in the PSlibrary repository. The wave functions and the electronic densities were expanded employing accurate cut-off energies of 6.80[Formula: see text]10[Formula: see text] and 5.44[Formula: see text]10[Formula: see text] eV, respectively. The electronic density was computed from the wave functions calculated at the [Formula: see text]-point in the first Brillouin-zone. Each structural optimization was minimized according to the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm, with force and energy convergence criteria of 25 meV[Formula: see text]Å[Formula: see text] and 1.36 meV, respectively. The electrostatic solvation effects were performed by the [Formula: see text] package with the Self-Consistent Continuum Solvation (SCCS) approach.

The effect of f-electrons on the structural phase transition, mechanical and electronic properties in light rare-earth bismuthides

ABSTRACT The electronic structure, phase transition pressure and mechanical properties of light rare-earth bismuthides (PrBi, NdBi, PmBi and SmBi) have been investigated by full geometry optimization using Vienna Ab-Initio Simulation Package (VASP) which has been used in combination with the projector augmented wave (PAW) method and the generalized gradient approximation (GGA) over the local density approximation (LDA) for exchange-correlation functional. We focus our attention on the lattice constants and elastic constants of these compounds. These compounds undergo a phase transition from the NaCl (B1) structure to the body-centered tetragonal (BCT) structure. We also report the density of states (DOS) of these rare earth bismuthides. In the case of PrBi and NdBi, the 4f states are treated as valence states. The effects of on-site Coulomb repulsion and the spin-orbit coupling (SOC) on the electronic structure are also studied.

Density functional theory calculations applied to olivine-like NaMnPO4 with transition metal substitutions for energy storage applications

In this study, Density Functional Theory (DFT) calculations are applied to evaluate the structural and thermodynamic properties of MPO4 and NaMPO4 as cathode materials for sodium-ion batteries (SIBs). Using the modified Perdew-Burke-Ernzerhof (PBE) method and the projector augmented wave (PAW) method, the effect of metal substitution in MPO4 and NaMPO4 lattices (M = Mn, Fe, Co, Ni,), as well as Fe-Ni substituted NaMnPO4 was examined for its structural and electrochemical characteristics. As NaMnPO4 has less ionic and electronic conductor, the partial substitution of Mn by simultaneous Ni and Fe gives good physicochemical properties useful for good cathode materials in SIBs. For NaMn0.5Ni0.25Fe0.25PO4, its optimal values of gravimetric capacity (154 mAh.g−1), bandgap energy (0.45 eV) and intercalation potential (3.54 V) appeared very interesting to be an attractive cathode material for SIBs. Na+ diffusion required less energy in NaFePO4, NaMnPO4, and Fe-Ni co-doped NaMnPO4 systems, promoting a rapid recharge rate and good ionic conductivity thanks to the desodiation process in creating a mixed oxidation state particularly for Fe and Mn atoms.

The interplay of density functional selection and crystal structure for accurate NMR chemical shift predictions.

Ab initio chemical shift prediction plays a central role in nuclear magnetic resonance (NMR) crystallography, and the accuracy with which chemical shifts can be predicted relative to experiment impacts the confidence with which structures can be assigned. For organic crystals, periodic density functional theory calculations with the gauge-including projector augmented wave (GIPAW) approximation and the PBE functional are widely used at present. Many previous studies have examined how using more advanced density functionals can increase the accuracy of predicted chemical shifts relative to experiment, but nearly all of those studies employed crystal structures that were optimized with generalized-gradient approximation (GGA) functionals. Here, we investigate how the accuracy of the predicted chemical shifts in organic crystals is affected by replacing GGA-level PBE-D3(BJ) crystal geometries with more accurate hybrid functional PBE0-D3(BJ) ones. Based on benchmark data sets containing 132 13C and 35 15N chemical shifts, plus case studies on testosterone, acetaminophen, and phenobarbital, we find that switching from GGA-level geometries and chemical shifts to hybrid-functional ones reduces 13C and 15N chemical shift errors by ∼40-60% versus experiment. However, most of the improvement stems from the use of the hybrid functional for the chemical shift calculations, rather than from the refined geometries. In addition, even with the improved geometries, we find that double-hybrid functionals still do not systematically increase chemical shift agreement with experiment beyond what hybrid functionals provide. In the end, these results suggest that the combination of GGA-level crystal structures and hybrid-functional chemical shifts represents a particularly cost-effective combination for NMR crystallography in organic systems.

1H and 13C chemical shift-structure effects in anhydrous β-caffeine and four caffeine-diacid cocrystals probed by solid-state NMR experiments and DFT calculations.

By using density functional theory (DFT) calculations, we refined the H atom positions in the structures of β-caffeine (C), α-oxalic acid (OA; (COOH)2), α-(COOH)2·2H2O, β-malonic acid (MA), β-glutaric acid (GA), and I-maleic acid (ME), along with their corresponding cocrystals of 2 : 1 (2C-OA, 2C-MA) or 1 : 1 (C-GA, C-ME) stoichiometry. The corresponding 13C/1H chemical shifts obtained by gauge including projector augmented wave (GIPAW) calculations agreed overall very well with results from magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy experiments. Chemical-shift/structure trends of the precursors and cocrystals were examined, where good linear correlations resulted for all COO1H sites against the H⋯O and/or H⋯N H-bond distance, whereas a general correlation was neither found for the aliphatic/caffeine-stemming 1H sites nor any 13C chemical shift against either the intermolecular hydrogen- or tetrel-bond distance, except for the 13COOH sites of the 2C-OA, 2C-MA, and C-GA cocrystals, which are involved in a strong COOH⋯N bond with caffeine that is responsible for the main supramolecular stabilization of the cocrystal. We provide the first complete 13C NMR spectral assignment of the structurally disordered anhydrous β-caffeine polymorph. The results are discussed in relation to previous literature on the disordered α-caffeine polymorph and the ordered hydrated counterpart, along with recommendations for NMR experimentation that will secure sufficient 13C signal-resolution for reliable resonance/site assignments.

The Mott transition in the 5d[formula omitted] compound Ba[formula omitted]NaOsO[formula omitted]: A DFT+DMFT study with PAW spinor projectors

Spin–orbit coupling has been reported to be responsible for the insulating nature of the 5d1 osmate double perovskite Ba2NaOsO6 (BNOO). However, whether spin–orbit coupling indeed drives the metal-to-insulator transition (MIT) in this compound is an open question. In this work we investigate the impact of relativistic effects on the electronic properties of BNOO via density functional theory plus dynamical mean-field theory calculations in the paramagnetic regime, where the insulating phase is experimentally observed. The correlated subspace is modeled with spinor projectors of the projector augmented wave method (PAW) employed in the Vienna Ab Initio Simulation Package (VASP), suitably interfaced with the TRIQS package. The inclusion of PAW spinor projectors in TRIQS enables the treatment of spin–orbit coupling effects fully ab-initio within the dynamical mean-field theory framework. In the present work, we show that spin–orbit coupling, although assisting the MIT in BNOO, is not the main driving force for its gapped spectra, placing this material in the Mott insulator regime. Relativistic effects primarily impact the correlated states’ character, excitations, and magnetic ground-state properties.