Projector Augmented Wave Potentials Research Articles

Polymorphs of Titanium Dioxide: An Assessment of the Variants of Projector Augmented Wave Potential of Titanium on Their Geometric and Dielectric Properties.

Titanium dioxide (TiO2) is one of the important functional materials owing to its diverse applications in many fields of chemistry, physics, nanoscience, and technology. Hundreds of studies on its physicochemical properties, including its various phases, have been reported experimentally and theoretically, but the controversial nature of relative dielectric permittivity of TiO2 is yet to be understood. Toward this end, this study was undertaken to rationalize the effects of three commonly used projector augmented wave (PAW) potentials on the lattice geometries, phonon vibrations, and dielectric constants of rutile (R-)TiO2 and four of its other phases (anatase, brookite, pyrite, and fluorite). Density functional theory calculations within the PBE and PBEsol levels, as well as their reinforced versions PBE+U and PBEsol+U (U = 3.0 eV), were performed. It was found that PBEsol in combination with the standard PAW potential centered on Ti is adequate to reproduce the experimental lattice parameters, optical phonon modes, and the ionic and electronic contributions of the relative dielectric permittivity of R-TiO2 and four other phases. The origin of failure of the two soft potentials, namely, Ti_pv and Ti_sv, in predicting the correct nature of low-frequency optical phonon modes and ion-clamped dielectric constant of R-TiO2 is discussed. It is shown that the hybrid functionals (HSEsol and HSE06) slightly improve the accuracy of the above characteristics at the cost of a significant increase in computation time. Finally, we have highlighted the influence of external hydrostatic pressure on the R-TiO2 lattice, leading to the manifestation of ferroelectric modes that play a role in the determination of large and strongly pressure-dependent dielectric constant.

Ab Initio Theoretical Study of DyScO3 at High Pressure

DyScO3 is a member of a family of compounds (the rare-earth scandates) with exceptional properties and prospective applications in key technological areas. In this paper, we study theoretically the behavior of DyScO3 perovskite under pressures up to about 65 GPa, including its structural and vibrational properties (with an analysis of the Raman and infrared activity), elastic response, and stability. We have worked within the ab initio framework of the density functional theory, using projector-augmented wave potentials and a generalized gradient approximation form to the exchange-correlation functional, including dispersive corrections. We compare our results with existing theoretical and experimental published data and extend the range of previous studies. We also propose a candidate high-pressure phase for this material.

Efficient Electronic Modulation of g-C 3 N 4 Photocatalyst by Implanting Atomically Dispersed Ag 1 -N 3 for Extremely High Hydrogen Evolution Rates

Efficient Electronic Modulation of g-C ₃ N ₄ Photocatalyst by Implanting Atomically Dispersed Ag ₁ -N ₃ for Extremely High Hydrogen Evolution Rates

Effect of the projector augmented wave potentials on the simulation of thermodynamic properties of vanadium

We report significant differences in high-pressure properties of vanadium at zero temperature and finite temperature when different projector augmented wave (PAW) potentials are used in simulations based on density functional theory. When a PAW potential with only five electrons taken as valence electrons is used, the cold pressures in the high-pressure region are seriously underestimated, and an abnormality occurs in the melting curve of vanadium at about 400 GPa. We show that the reason for these discrepancies lies in the differences in the descriptions of the interatomic force, electron dispersion, and anisotropy of electron bonding obtained from different PAW potentials at high pressure, which lead to striking differences in the mechanical stability of the system. We propose a procedure for selecting PAW potentials suitable for simulations at high temperature and high pressure. Our results provide valuable guidance for future simulations of thermodynamic properties under extreme conditions.

Comparative study of half-metallic ferromagnetic behaviour in ZnO monolayer doped with boron and carbon atoms

Electronic band structures of B- and C-doped ZnO monolayers (ML) at high doping concentration are studied based on spin-polarized plane-wave DFT with Projector Augmented Wave Potentials and Generalized Gradient Approximation. Our results show that both the B- and C-doped structures at 3.13% impurity atom per supercell exhibit half-metallic ferromagnetic behaviour due to the spin-polarized 2p orbitals of the dopant atom, which are localized within the energy gap of the host lattice. A net magnetic moment of 1μB and 2μB are, respectively, found in the B- and C-doped structures mainly due to the partially filled dopant atom 2 p orbitals. Due to ferromagnetic coupling, magnetic moments from the neighbouring Zn atoms and the subsequent O atoms also contribute to the net magnetic moment. At a higher doping concentration of 6.25% impurity atom per supercell, both the materials completely transformed into metal. It is also found that while C doping maintains its ferromagnetic property at this doping concentration, the B-doped ZnO ML becomes antiferromagnetic metal. Our findings would provide valuable theoretical data for material scientists in fabrication of the doped ZnO ML in laboratory

Light-Responsive Proton Conductor: Record High Gain of Proton Conductivity Achieved by Photoinduced Electron-Transfer Strategy

Light-Responsive Proton Conductor: Record High Gain of Proton Conductivity Achieved by Photoinduced Electron-Transfer Strategy

Czochralski growth, electronic structure, luminescence and scintillation properties of Cs2Mo3O10: A new scintillation crystal for 0νββ decay search

A new molybdenum (Mo) based Cesium tri-molybdate (Cs2Mo3O10) single crystal scintillator has been grown successfully by the Czochralski technique. The crystal growth conditions such as pulling, rotation and cooling rate were optimized for crack free high-quality single crystals. The electronic band structure has been calculated with density functional theory using projector augmented wave potentials as implemented in the Vienna ab initio Simulation Package. The major contribution in the formation of valence band near the fermi level is observed from Mo and O p orbitals while the bottom of the conduction band mainly consists from Mo-d and O-p states. The grown crystal possesses good transparency above the fundamental absorption edge in the wavelength range of 400–900 nm. Optical band gap of 3 eV is estimated from the absorption spectra measured at room temperature. Luminescence and scintillation properties were measured in the temperature range of 10–300 K under the excitation of UV light at 4.42 eV, X-rays and beta rays. The emission spectrum measured at 230 K is comprising of a single band peaking at 645 nm, which intensity is enhanced with the cooling of crystal. A single exponential photoluminescent decay time of 43 μs is obtained at 220 K which further slows down upon cooling of the crystal and found to be 1.64 ms at 10 K. The scintillation light yield of Cs2Mo3O10 crystal at 10 K is found to be 185% of Li2MoO4 (LMO) crystal. The thermally stimulated luminescence (TSL) kinetic parameters such as trap depth and frequency factor from the glow curve measured after X-ray irradiation at 10 K, have been determined using general order kinetics. A possibility of crystal growth with large volume, good optical, luminescence and scintillation properties reveal that this scintillation material can be a good candidate for the neutrinoless double beta (0νββ) decay search of 100Mo.

The Predictive Power of Different Projector-Augmented Wave Potentials for Nuclear Quadrupole Resonance

The projector-augmented wave (PAW) method is used to calculate electric field gradients (EFG) for various PAW potentials. A variety of crystals containing reactive nonmetal, simple metal, and transition elements, are evaluated in order to determine the predictive ability of the PAW method for the determination of nuclear quadrupole resonance frequencies in previously unstudied materials and their polymorphs. All results were compared to experimental results and, where possible, to previous density functional theory (DFT) calculations. The EFG at the 14N site of NaNO2 is calculated by DFT for the first time. The reactive nonmetal elements were not very sensitive to the variation in PAW potentials, and calculations were quite close to experimental values. For the other elements, the various PAW potentials led to a clear spread in EFG values, with no one universal potential emerging. Within the spread, there was agreement with other ab initio models.

Computational characterization of the structural and mechanical properties of AlxCoCrFeNiTi1−x high entropy alloys

AlCoCrFeNiTi is one kind of high entropy alloys with potential applications in aerospace, electronics and machinery manufacturing, etc. Its microstructure, thermodynamic and mechanical properties vary with Al and Ti contents. The disordered structures of AlxCoCrFeNiTi1−x (x = 0–1.0) alloys were generated and screened with the special quasi-random method. First-principles calculations with the Perdew–Burke–Ernzerhof functional and projector-augmented wave potential were carried out to further identify the structures and assess their thermodynamic and mechanical properties. The measured lattice constants and observed phase transition from bcc to fcc with Ti addition and Al reduction were reproduced in the calculations. The predicted transition point is at the Al content of about 8 at%. The heat capacity of the bcc and fcc structures exhibit similar temperature dependence, matching well with the empirical Dulong-Petit Model and the quantum Debye Model. The elastic constants and elastic moduli vary with the phase structures and compositions. The studied AlxCoCrFeNiTi1−x alloys are predicted to possess good comprehensive mechanical performances, especially for x = 0.8 and 0.6 for the bcc structures and x = 0.5 for the fcc structures. The addition/reduction of Al atoms from the systems alters the electron localization/delocalization that has considerable influence on the interatomic interaction strength in the alloy systems.

Exploring the chemical nature of super-heavy main-group elements by means of efficient plane-wave density-functional theory.

The design, implementation, and evaluation of a computationally efficient approach for exploring the chemical nature and bulk properties of the super-heavy main-group elements (SHEs) Cn-Og with nuclear charges of Z = 112-118 is described. The approach combines plane-wave density-functional theory (DFT) based on a newly devised set of projector-augmented wave potentials (PAWs) with the D3 dispersion correction, whose parameter-space is extended for this purpose. Regarding both, the fitting of the PAWs as well as the calculation of the D3 parameters, it is shown that the peculiar electronic structure of the SHEs with strong relativistic effects makes it necessary to adapt the well established computational protocols. Eventually, the methodology is tested employing various common functionals (PW91, PBE, PBE-D3, PBE0-D3, PBEsol and SCAN) by comparison to experimental and high-level results for the bulk of Cn and Og, as well as by calculating adsorption energies of Cn-Og on a gold surface and comparing these to the lighter congeners Hg-Rn as well as experimentally derived data. These tests establish that our approach provides a consistent and accurate description of the reactivity of the SHEs and is largely in excellent agreement with experimental and high-level references, and moreover underline the great relevance of dispersion interactions, as well the game-changing impact of spin-orbit coupling on SHE reactivity. Ultimately, the conducted calculations provide novel insights into the chemical behavior and nature of the SHEs, showcase the breakdown of periodic trends in the seventh period, and allow us to revisit and confirm an empirical relation between adsorption on gold and the cohesive energy.

Theoretical insight into the optoelectronic properties of lead-free perovskite derivatives of Cs3Sb2X9 (X = Cl, Br, I)

The lead-free perovskites derivatives of Cs3Sb2X9 (X = Cl, Br, I) have been synthesized, but their photocatalytic properties are not explored. To evaluate the feasibility for the visible light catalytic performance, we calculate the structural, electronic, optical and charge transfer properties of Cs3Sb2X9, based on the hybrid density functional theory of HSE06 with the projector augmented wave potential. The results show the decrease of band energy gaps and the redshift of absorption edges from X = Cl to I. The absolute potential of the valence band maximum and conduction band minimum is determined to justify the feasibility of the photocatalytic water splitting or CO2 reduction. The calculated carrier mobilities reveal that the high electron mobilities of Cs3Sb2I9 are beneficial to the reducing powers for hydrogen generation and CO2 reduction. The present results indicate that Cs3Sb2I9 is appropriate for the photocatalytic water splitting to produce hydrogen or the CO2 reduction driven by the visible light.

Electronic and elastic properties of Ba2HgSn and Ca2HgSn Rattling Heusler

Semiconductor electronic components are the active elements of integrated circuits, and they are at the origin of all advances in electronics. A new semiconductor class consists in Rattling Heusler. The purpose of this work is to study the structural, electronic and elastic properties of X2HgSn (X = Ba, Ca) Heusler alloys by using the first-principle projector augmented wave potential within the generalized gradient approximation. Our calculations show that these compounds are all semiconductor and are ductile manner.

Density Functional Theory Study of Structural and Electronic Properties of γ'-Ni3Al and γ"-Ni3Nb

In the present paper, the structural and electronic properties of ordered face-centered cubic (L12) γ'-Ni3Al and body-centered tetragonal (D022) γ"-Ni3Nb are investigated by density functional theory calculation within projector augmented wave (PAW) potentials. The structures are optimized for both the phases and the results are found in good agreement with the experimental and theoretical data. In the geometrical optimization, all the forces on each atom are converged to less than 103 eV/Å, and the total energy less than 10-6 eV/atom. The Methfessel–Paxton smearing width of 0.2 eV is used here. The formation energy of γ'-Ni3Al and γ"-Ni3Nb phases are calculated and the values are found to be -40.67 kJ/mol and -27.55 kJ/mol respectively. The bonding character is analyzed based on the density of states (DOS).

DFT study on phase transition behavior and mechanical properties of HgSe polymorphs under high pressure

Total energy calculations based on density functional theory are performed for HgSe in the ambient and pressure induced phases. The electronic exchange and correlation effects are described by employing the generalized gradient approximation together with the projector augmented wave potentials. The equation of state parameters and the phase transition paths are obtained from the energy-volume landscape and enthalpy versus pressure data, correspondingly. The observed phase transition sequence of HgSe as ZB → Cinnabar → RS → Cmcm and the final transition from Cmcm to CsCl structure predicted by the other theoretical study are confirmed by our calculations. The pressure dependence of elastic constants of the structures considered in this study is reported. Bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and Debye temperature as isotropic mechanical properties are evaluated for HgSe polymorphs. Our calculations of energy band structure reveal the inverted band structure evoking that HgSe in ZB phase is a semimetal.

Enhancement of the optical absorption of carbon group elements doped ZnS in the visible light range

Abstract Although the pristine ZnS can perform photocatalytic hydrogen production from water splitting, the reaction can not be driven by the visible light because of its wide energy band gap. Therefore, ZnS doped with carbon group elements (C, Si, Ge, Sn, Pb) has been investigated by using first-principles density functional theory calculations to understand the feasibility of the reaction driven by solar energy. All the geometrical structures are fully optimized. The electronic and optical properties of these structures have been calculated with the meta-GGA + MBJ method and with projector augmented wave potential. The results show that all the doped structures have low formation energies, implying that the synthesis of the doped structures is not difficult in energy. Moreover, the absorptions of the doped structures in the visible light range are significantly enhanced, but their energy levels are still suitable for water splitting to generate hydrogen, which means that carbon group elements doped ZnS structures are promising candidate materials for water splitting driven by visible light.

Adsorption and diffusion on a phosphorene monolayer: a DFT study

A computational study of the adsorption and diffusion behavior of alkali and alkaline earth metal atoms on a phosphorene monolayer is reported. Our calculations were performed within the framework of density functional theory using the Perdew–Burke–Ernzerhof functional and projector augmented wave potentials, as derived from the generalized gradient approximation. Our binding energy calculations for various potential adsorption sites showed that the site located above the center of a triangle formed by three surface phosphorus atoms is the most attractive to all adatoms. In addition, simulation of the diffusion of adatoms across the surface of the phosphorene monolayer showed that the diffusion is anisotropic, with K having the lowest diffusion barrier (0.02 eV along the zigzag pathway). To the best of our knowledge, this is the lowest diffusion barrier of any metal adatom on a single layer of phosphorene. While phosphorene exhibited significantly better adatom adsorption and diffusion than graphene, it also showed a reduced storage capacity compared to graphene, most probably due to the structural distortion induced by the oversaturated phosphorene surface. This finding strongly suggests that a phosphorene–graphene hybrid system could be employed as a promising high-capacity ion anode.

Influence of optical non-uniformity on the reflectance of dense plasmas

We provide theoretical analysis of the reflectance of shock compressed plasmas and warm dense matter for normal incidence of laser radiation as well as for the dependence of s- and p-polarized reflectivity on incidence angle. We use density functional theory approach for the calculation of the dielectric function and reflectivity. The Kohn-Sham set of equations with the projector augmented wave (PAW) potential is solved for valent electrons. Due to the nonlocality of the PAW potentials, the longitudinal expression for the imaginary dielectric function is used. The real part is obtained by the Kramers-Kronig transformation. Quantum molecular dynamics simulation and VASP is used. Comparison with the experimental data for shock compressed xenon is performed. Three wavelengths are considered.

Self-consistent parametrization of DFT +Uframework using linear response approach: Application to evaluation of redox potentials of battery cathodes

The accuracy of $\mathrm{DFT}+U$ calculations, applied to the study of electronic structure and energetics of strongly correlated materials, heavily depends on $U$ parameters, chosen for adequate treatment of $d$ and $f$ states. Computational evaluation of $U$ parameters, which does not require fitting to experimental measurements or results of computationally expensive schemes, is highly desirable for the study of novel materials and even more so for materials not yet synthesized to date. Within this work, we show that the linear response method could provide $U$ parameters which can yield redox potentials of battery cathode materials in much better agreement with experiment than conventional density functional theory (DFT). In our approach, we evaluate $U$ values self-consistently, ensuring agreement between $U$ calculated using linear response with the value used for $\mathrm{DFT}+U$ calculations. We find that such self-consistency is necessary for determination of adequate values of $U$. We also studied the impact of using various PAW (projector augmented wave) potentials for transition-metal ions, that differ by the number of electrons treated as valence. We find that redox potentials are reasonably well reproduced for all cases, although a slightly higher degree of accuracy corresponds to PAW potentials with semicore electrons treated as valence. Importantly, we find that converged values of $U$ are substantially different for various PAW potentials of transition-metal ions of the same material. Overall, we find that self-consistent $\mathrm{DFT}+U$/linear response calculations provide quite accurate values of redox potentials for materials with purely ionic bonding (e.g., ${\mathrm{LiFePO}}_{4}$, ${\mathrm{LiCoPO}}_{4}$, ${\mathrm{LiCoO}}_{2}$, ${\mathrm{LiMnPO}}_{4}$, ${\mathrm{NaFePO}}_{4}$), whereas for materials with covalent $pd$ hybridization (e.g., ${\mathrm{LiNiO}}_{2}$) or conducting materials (e.g., ${\mathrm{LiTiS}}_{2}$) the agreement with experimental redox voltage is lower. This emphasizes the need for application of more advanced techniques (e.g., $\mathrm{DFT}+U+V$ method) for accurate study of partially covalent and metallic materials, which contain transition-metal ions.

Effects of S and N doping on the structural, magnetic and electronic properties of rutile CrO2

Magnetic and electronic properties of S- and N-doped CrO2 are studied by using the first-principle projector augmented wave potential within the generalized gradient approximation. The optimized lattice constants for CrO2 agree well with the previous work. With increasing S doping (N doping), the lattice constants of CrO2−xSx (CrO2−xNx) (x=0.5, 1 and 1.5) all increase (decrease), While these compounds remain the tetragonal structure. CrO1.5S0.5, CrO1.5N0.5 and CrON compounds remain the half-metallicity, while the band gap is determined by different factors. It is also found that the change of the total magnetic moment with equivalent atom S doping in CrO2 compound is small except for x=1.

Ab-initio electronic structure calculations and properties of [SixSn1 − x]3N4 ternary nitrides

We carry out ab initio electronic structure calculations of (SixSn1−x)3N4 using density functional theory with projector augmented-wave potentials under the generalized gradient approximation. We find that the energetically favorable structure of Sn3N4 is the face-centered cubic spinel structure, followed by the hexagonal structure which has energy band gaps of 1.85eV and 1.44eV respectively. The (SixSn1−x)3N4 ternary compound can exhibit both cubic and hexagonal crystal structures over the full range of x. However, the cubic structure is found to be energetically favorable for x<0.3 above which the hexagonal structure of (SixSn1−x)3N4 dominates. The energy band gap can be tuned continuously from 1.44eV up to 5.8eV in the case of the hexagonal crystal structure of (SixSn1−x)3N4 and from 1.85eV to 4.82eV in the case of cubic (SixSn1−x)3N4. Nevertheless the energy gap of (SixSn1−x)3N4 is direct only for x<0.3 when it is cubic and for x<0.5 when hexagonal.