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This work analyzes the effects of a nearby Hf or Zr dopant on the electron density trapped at an oxygen vacancy site. The two metals are among the dopants used to achieve thermoluminescence and energy storage in phosphors based on cubic lutetium oxide (c‐Lu2O3). The presence of oxygen vacancies is anticipated in those phosphors. If the dopant is located outside the immediate surroundings of the vacancy site, the resulting optical trap depth is similar to that of the isolated oxygen vacancies (1.6–1.7 eV versus 1.7 eV). If the dopant is one of the four metal cations surrounding the vacancy site, the corresponding trap depth is 2.0–2.1 eV. Using time‐dependent density‐functional theory calculations, it was found that the excitation of the vacancy‐trapped electrons can take two forms: a local excited state at the vacancy site can be formed, or an electron transfer to Hf might occur. With charge compensation in mind, several structures with three defects were analyzed: the dopant cation, the vacancy and an interstitial oxygen (Hf/Zr plus a Frenkel pair). These last two systems with the dopant in a +4 oxidation state and a single electron trapped at the vacancy site correspond to zero total charge, while another electron can be trapped. The vacancy site is expected to trap the electron, not the dopant. The composite defects of the dopant and Frenkel pair are thus considered the most likely electron traps in cubic Lu2O3:Hf and cubic Lu2O3:Zr. [ABSTRACT FROM AUTHOR]

We investigated the magnetic alignment and formation energy of Niobium (Nb) in magnetite using density functional theory (DFT) calculations with both GGA + U and meta-GGA approaches. Our findings revealed that Nb exhibits greater stability when located at the octahedral site within the compound, although it remains metastable overall. By analyzing the deviation of the Nb-O bond from its expected ionic behavior, we have gained valuable insights into how Nb influences the magnetic moment in Nb-doped magnetite, which was determined to be 3.275 μ B /f.u. Moreover, examination of the bond angles has provided further justification for the observed reduction in this magnetic moment compared to pristine magnetite, where it is ∼ 4.0 μ B /f.u. This study yields significant insights into doped magnetite, a crucial industrial compound. • The stability and magnetism of niobium-doped magnetite are investigated. • Density functional theory based on GGA+ U and Meta-GGA functionals was used. • Nb dopant is more stable when substituting a Fe at the octahedral site. • Nb doping decreases the saturation magnetization of magnetite. • Nb-doped Fe 3 O 4 is metastable, while NbFe 2 0 4 constitutes the ground state. [ABSTRACT FROM AUTHOR]

A number of Lu2O3-based materials were reported to present efficient capability of trapping excited charge carriers in metastable excited states formed either by specific dopants or naturally occurring defects. Over the years, abundant experimental data have been collected, which were taken as a solid ground to treat the problem using computational chemistry. Density functional theory (DFT) calculations with an advanced meta generalized gradient approximation (mGGA) functional were used to analyze electron trapping in cubic Lu2O3 doped with Hf. Individual ions of dopant and nearest-neighbor dopant ion pairs were considered. The effects of interstitial anions such as O2- and Cl- were analyzed. In most of the analyzed cases the additional electron charge is localized at the dopant site. However, in many of the studied cases, the dopant/defect states overlap with the conduction band and cannot correspond to electron trapping. The Hf3+ ion in the Lu site of C3i local symmetry (Hf Lu-C3i ) corresponds to a moderate trap depth of 0.8-0.9 eV. Several composite defects corresponding to deeper (1.1-1.4 eV) traps also exist. Unambiguous deep traps (1.5-1.8 eV) correspond to systems with Hf dopant in the cationic void, accompanied by two interstitial oxygen atoms. The results thus indicate that basic 'Hf-substitutes-Lu' doping is unlikely to correspond to the deep traps observed experimentally in Lu2O3:Tb,Hf andLu2O3:Pr,Hf and more complex defects must be involved. [ABSTRACT FROM AUTHOR]

A number of Lu2O3‐based materials were reported to present efficient capability of trapping excited charge carriers in metastable excited states formed either by specific dopants or naturally occurring defects. Over the years, abundant experimental data have been collected, which were taken as a solid ground to treat the problem using computational chemistry. Density functional theory (DFT) calculations with an advanced meta generalized gradient approximation (mGGA) functional were used to analyze electron trapping in cubic Lu2O3 doped with Hf. Individual ions of dopant and nearest‐neighbor dopant ion pairs were considered. The effects of interstitial anions such as O2− and Cl− were analyzed. In most of the analyzed cases the additional electron charge is localized at the dopant site. However, in many of the studied cases, the dopant/defect states overlap with the conduction band and cannot correspond to electron trapping. The Hf3+ ion in the Lu site of C3i local symmetry () corresponds to a moderate trap depth of 0.8–0.9 eV. Several composite defects corresponding to deeper (1.1–1.4 eV) traps also exist. Unambiguous deep traps (1.5–1.8 eV) correspond to systems with Hf dopant in the cationic void, accompanied by two interstitial oxygen atoms. The results thus indicate that basic `Hf‐substitutes‐Lu' doping is unlikely to correspond to the deep traps observed experimentally in Lu2O3:Tb,Hf andLu2O3:Pr,Hf and more complex defects must be involved.Density functional theory (DFT) calculations with an advanced meta generalized gradient approximation (mGGA) functional were used to analyze electron trapping in cubic Lu2O3 doped with Hf. Basic `Hf‐substitutes‐Lu' doping does not correspond to the deep traps observed experimentally in Lu2O3:Tb,Hf and Lu2O3:Pr,Hf, while more complex defects likely do. [ABSTRACT FROM AUTHOR]

The 9R phase model based on experimental orientation relationship are constructed, the mechanical moduli of the face-centered cubic (FCC) and 9R phases in CrCoNi medium-entropy alloy (MEA) are investigated by first-principles calculations with the meta-generalized gradient approximation (meta-GGA) functional. This functional accurately describes CrCoNi MEA, captures localized electronic states, and overcomes the challenge of DFT + U parameters in special quasi-random structure (SQS) based transition metal atom models. Results indicate that the 9R phase exhibits higher mechanical moduli than the FCC phase, with a 12% increase in bulk modulus and a 7% increase in Poisson's ratio. Consequently, the strength and toughness of CrCoNi MEA are significantly enhanced. Doping Mo, Ta, and W in the MEA structures improves strength by promoting the formation of the 9R phase compared to the doped single FCC phase. Calculations of the work of adhesion and fracture toughness for the 9R/FCC interface reveal improved interface properties with Mo and W doping. These enhancements are attributed to the hybridization of electronic orbitals in the doped CrCoNi MEA, resulting in changes in bond types between neighboring atoms and subsequent modifications of mechanical properties in the 9R phase. Comparative computational values strongly support an alloy design strategy involving Mo doping and the construction of the 9R phase to achieve superior mechanical properties in MEA. [Display omitted] • The GSFE from Meta-GGA showed trends akin to GGA calculations, but distinct values. • The formation of the 9R phase was explored through pioneering computational insights. • Doping effect on the interface toughness of the 9R phase of CrCoNi MEA was studied. [ABSTRACT FROM AUTHOR]

Despite significant advances in first-principles calculation methods, there is no single exchange-correlation functional which predicts the ground state of materials without an error yet. We investigated how accurately ground states of binary semiconductors are described using 16 exchange-correlation functionals (with or without van der Waals corrections). LDA, PBEsol, SCAN (with or without rVV10 correction), and PBE with D3 van der Waals correction (zero or Becke-Johnson damping) show good predicting power. The lattice constants of stable phases were slightly better described by SCAN, PBEsol, PBE+D3 (Becke-Johnson damping), and MS2. We also propose a set of functionals to double-check the stability of new materials based on the majority vote. [ABSTRACT FROM AUTHOR]

This work examines the suitability of meta-GGA functionals for symmetry-adapted perturbation theory (SAPT) calculations. The assessment is based on the term-by-term comparison with the benchmark SAPT variant based on coupled-cluster singles and doubles description of monomers, SAPT(CCSD). Testing systems include molecular complexes ranging from strong to weak and the He dimer. The following nonempirical meta-GGAs are examined: TPSS, revTPSS, MVS, SCAN, and SCAN0 with and without the asymptotic correction (AC) of the exchange-correlation potential. One range-separated meta-GGA functional, LC-PBETPSS, is also included. The AC-corrected pure meta-GGAs (with the exception of MVS) represent a definite progress in SAPT(DFT) compared to pure GGA, such as PBEAC, with their more consistent predictions of energy components. However, none of the meta-GGAs is better than the hybrid GGA approach SAPT(PBE0AC). The SAPT(DFT) electrostatic energy offers the most sensitive probe of the quality of the underlying DFT density. Both SCAN- and TPSS-based electrostatic energies agree with reference to within 5% or better which is an excellent result. We find that SCAN0 can be used in SAPT without the AC correction. The long-range corrected LC-PBETPSS is a reliable performer both for the components and total interaction energies. [ABSTRACT FROM AUTHOR]

Highlights • The band gap and effective masses are highly dependent on NW diameter and orientation. • Strain particularly affect effective masses of the 1 × 1 nm2 [1 1 1]-oriented NWs. • Strain engineering can improve device characteristics in InAs nanowires. • Controlling process induced strain is critical for uniform device characteristics. Abstract The impact of uni-axial compressive and tensile strain and diameter on the electronic band structure of indium arsenide (InAs) nanowires (NWs) is investigated using first principles calculations. Effective masses and band gaps are extracted from the electronic structure for relaxed and strained nanowires. Material properties are extracted and applied to determine charge transport through the NWs described within the effective mass approximation and by applying the non-equilibrium Green’s function method. The transport calculations self-consistently solve the Schrödinger equation with open boundary conditions and Poisson’s equation for the electrostatics. The device structure corresponds to a metal oxide semiconductor field effect transistor (MOSFET) with an InAs NW channel in a gate-all-around geometry. The channel cross sections are for highly scaled devices within a range of 3 × 3–1 × 1 nm2. Strain effects on the band structures and electrical performance are evaluated for different NW orientations and diameters by quantifying subthreshold swing and ON/OFF current ratio. Our results reveal for InAs NW transistors with critical dimensions of a few nanometer, the crystallographic orientation and quantum confinement effects dominate device behavior, nonetheless strain effects must be included to provide accurate predictions of transistor performance. [ABSTRACT FROM AUTHOR]

Density-functional approximations developed in the past decade necessitate the use of quadrature grids that are far more dense than those required to integrate older generations of functionals. This category of difficult-to-integrate functionals includes meta-generalized gradient approximations, which depend on orbital gradients and/or the Laplacian of the density, as well as functionals based on B97 and the popular 'Minnesota' class of functionals, each of which contain complicated and/or oscillatory expressions for the exchange inhomogeneity factor. Following a strategy introduced previously by Gill and co-workers to develop the relatively sparse 'SG-0' and 'SG-1' standard quadrature grids, we introduce two higher-quality grids that we designate SG-2 and SG-3, obtained by systematically 'pruning' medium- and high-quality atom-centered grids. The pruning procedure affords computational speedups approaching a factor of two for hybrid functionals applied to systems of [ABSTRACT FROM AUTHOR]

The scaling of neutral atoms to largeZ, combining periodicity with a gradual trend to homogeneity, is a fundamental probe of density functional theory, one that has driven recent advances in understanding both the kinetic and exchange-correlation energies. Although research focus is normally upon the scaling of integrated energies, insights can also be gained from energy densities. We visualise the scaling of the positive-definite kinetic energy density (KED) in closed-shell atoms, in comparison to invariant quantities based upon the gradient and Laplacian of the density. We notice a striking fit of the KED within the core of any atom to a gradient expansion using both the gradient and the Laplacian, appearing as an asymptotic limit around which the KED oscillates. The gradient expansion is qualitatively different from that derived from first principles for a slowly varying electron gas and is correlated with a nonzero Pauli contribution to the KED near the nucleus. We propose and explore orbital-free meta-GGA models for the kinetic energy to describe these features, with some success, but the effects of quantum oscillations in the inner shells of atoms make a complete parametrisation difficult. We discuss implications for improved orbital-free description of molecular properties. [ABSTRACT FROM PUBLISHER]

In this work, we study the structural and electronic properties of TiO2 in the rutile phase based on first principles calculations. The electronic exchange and correlation effects were studied using functionals in the local density approximation (LDA), the generalized gradient approximation (GGA) by Perdew-Burke- Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang 91 (PW91) and revised Perdew-Burke-Ernzerhof (rPBE), and the meta-generalized gradient approximation (meta-GGA) by Tao-Perdew-Staroverov-Scuseria (TPSS) and revised-TPSS (RTPSS) in the frame of the Density Functional Theory (DFT). We found that the PBEsol functional provides better results for the lattice parameter values (a y c) and the equatorial and axial lengths (deq and dax); while for the cohesion energy (Ecoh), volumetric module (B0) and angles (2q y a) the PBE, rPBE and TPSS functionals respectively, are closer to the experimental values. It is confirmed that the TiO2 presents properties of direct semiconductor in Γ-Γ. [ABSTRACT FROM AUTHOR]

We present the theory of semilocal exchange-correlation (XC) energy functionals which depend on the Kohn-Sham kinetic energy density (KED), including the relevant class of meta-generalized gradient approximation (meta-GGA) functionals. Thanks to the KED ingredient, meta-GGA functionals can satisfy different exact constraints for XC energy and can be made one-electron self-correlation free. This leads to a better accuracy over a wider range of properties with respect to GGAs, often reaching the accuracy of hybrid functionals, but at much reduced computational cost. An extensive survey of the relevant literature on existing KED dependent XC functionals is provided, considering nonempirical, semi-empirical, and fully empirical ones. A deeper analysis and a wide benchmark are presented for functionals derived considering only exact constraints and parameters obtained from model and/or atomic systems. [ABSTRACT FROM AUTHOR]

Exchange-correlation density functionals at the meta-generalised gradient approximation level typically use the Kohn–Sham orbitals as an ingredient to create the isoorbital indicator, whereis the von Weizsäcker kinetic energy density andis the kinetic energy density of the Kohn–Sham orbitals. When a magnetic field is included in the treatment, the Kohn–Sham orbitals vary with the vector-potential gauge, as doesand implicitly the exchange-correlation energy. However, it is a known result in current density functional theory that the exact exchange-correlation energy is gauge independent. Three different gauge-independent replacements forhave been proposed by other authors. Only one of these is, however, known to stay between 0 and 1. We modify one of the others, the Maximoff–Scuseria isoorbital indicator, so that it also stays between 0 and 1. We investigate the ability of the isoorbital indicators evaluated in a system with densityand paramagnetic current densityto reproduce the value ofin a system having no paramagnetic current, but the same density. We provide the first example known to us where the Tao–Perdew isoorbital indicator goes outside of the interval from 0 to 1. [ABSTRACT FROM AUTHOR]

• Multiple DFT methods were evaluated for the simulation of metal-supported metal nanoislands. • Triatomic clusters of Pt on Au(111) are more stable with a linear conformation while those of Pd are more stable with a triangular conformation. • Pt and Pd clusters with four or more atoms on Au(111) prefer non-linear conformation. • The various DFT methods yield different energy for the adsoriton of hydrogen on Pt and Pd nanoislands on Au. We have evaluated various density functional theory (DFT) methods to simulate geometric, energetic, electronic, and hydrogen adsorption properties of metal-nanoparticles supported on metal surfaces. We used Pt and Pd nanoislands on Au(111) as model systems. The evaluated DFT methods include GGA (PW91, PBE, RPBE, revPBE, and PBESol), GGA with van der Waals (vdW) corrected (PBE-D3), GGA with optimized vdW functionals (revPBE-vdW), meta-GGA (SCAN and MS2), and the machine learning-based method BEEF-vdW. The results show that the various DFT methods yield similar geometric and electronic properties for Pt (or Pd) nanoislands on Au(111). The DFT methods also produce similar relative energetics for small Pt (or Pd) clusters with different conformations on Au(111). The results show that a triatomic cluster of Pt on Au(111) is more stable with a linear conformation. In contrast, a triatomic cluster of Pd is more stable with a triangular conformation. For clusters with four or more atoms, Pt and Pd clusters on Au(111) prefer non-linear conformation. We found that the various DFT methods yield different results only for the adsorption energy of hydrogen. [Display omitted] [ABSTRACT FROM AUTHOR]

The performance of modern density functionals for the prediction of molecular hyperfine couplings is investigated for a series of small radicals and transition metal complexes. Besides the established BP86 (GGA) and B3LYP (hybrid) functionals we have tested two prototypical members of emerging classes of density functionals, namely the TPSS meta-GGA functional (together with its hybrid version TPSSh) and the B2PLYP double-hybrid functional. The latter is the first member of a 'fifth-rung' density functional that incorporates a fraction of orbital dependent nonlocal correlation energy estimated at the level of second-order many-body perturbation theory. Since this approach is non-variational, it becomes necessary to derive and implement the so-called 'relaxed' densities in order to properly predict hyperfine couplings. The necessary formalism is described in some detail and the new method has been implemented into the ORCA electronic structure program. The results of extended test calculations reveal that TPSS is superior to BP86. The hybrid variant TPSSh is at least as accurate or better than the B3LYP functional and significantly superior to the non-hybrid TPSS variant. The B2PLYP functional also leads to accurate predictions and is a clear improvement for the difficult metal nucleus HFCs. However, it also showed a few significant outliers in the test set which points to a somewhat reduced stability in the method. The latter effect is largely attributed to the elevated fraction Hartree-Fock exchange (53%) and to some extent also to the perturbative correction. [ABSTRACT FROM AUTHOR]

The recent generalized gradient approximation (GGA) density functional OCS1 of Handy and Cohen is implemented in the deMon code and tested on a carefully selected set of problems. OCS1 is found to be accurate for molecular atomization energies, transition metal–ligand bonds, and systems with intramolecular hydrogen bonds. However, OCS1 encounters problems for systems with intermolecular hydrogen bonds. It also tends to elongate bond lengths systematically, and sometimes significantly. The OPTX exchange is combined with three meta-GGA correlation functionals, Lap3, τ1, and τ2, the latter reported for the first time. The new meta-GGA scheme OPTX exchange plus τ2 correlation called Oτ2 yields improved molecular geometries, NMR shielding constants, and an improved barrier height for the H+H2 reaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [ABSTRACT FROM AUTHOR]

• Adsorption characteristics of NH 3 , NO, NO 2 , CO and CO 2 molecules on a black phosphorene are explored using state-of-the-art computational DFT methods. • All molecules are shown to adsorb on the phosphorene surface with different favorite adsorption sites, depending on the molecule geometry and orientation. • At high coverages, the calculated adsorption energies per molecule show that the molecule-molecule interactions for the SCAN+rVV10 is stronger than that for the optB88-vdW functional showing new insights for the role of meta-GGA. Using Density Functional Theory (DFT), we perform a detailed computational study to explore the adsorption behaviors of NH 3 , NO, NO 2 , CO and CO 2 gas molecules on a black phosphorene surface at several coverages. Van der Waals (vdW) interactions were taken into account within the optB88-vdW functional. In addition, a comparison with the strongly-constrained and appropriately-normed (SCAN) meta-generalized gradient approximation (meta-GGA) is discussed. Our calculations show that all molecules adsorb on the surface of black phosphorene with different favorable adsorption sites, depending on the molecule's geometry and orientation. Alongside the adsorption energies, other properties are presented including the adsorption distances and charge transfers. At high coverages, the adsorption energies per molecule show that the functionals start to behave differently as the coverage rate increases. The significant charge transfer between NO and NO 2 molecules and black phosphorene suggests its potential integration towards efficient nitrogen-oxide detectors. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, electronic, thermoelectric and optical properties of partially fluorinated borophene were investigated in the framework of density functional theory. The calculations performed by standard generalized gradient approximation (GGA) as well as meta -GGA. The bandgap energy increased from 0.4 eV by GGA to 0.87 eV in the case of meta -GGA. Thermoelectric property investigations revealed the figure of merit close to unity while the thermoelectric performance of the monolayer improved by meta -GGA calculations. The real and imaginary parts of the dielectric function exhibited optical anisotropic behaviors. • Electronic, optical & TE properties of B 2 F monolayer were investigated by DFT through PBE and TB09 functional. • Band gap energy increased to 0.87 eV when the meta-GGA-TB09 was used. • The quality of B 2 F for TE applications were estimated by dimensionless figure of merit as a function of chemical potential. • The B 2 F monolayer showed optical anisotropic behavior while having absorption edge in mid/near infrared and visible region. [ABSTRACT FROM AUTHOR]

Electronic structure of Ta-doped cubic (bixbyite-type) lutetium oxide was analyzed using augmented plane wave with local orbitals density functional theory (DFT) calculations with meta-generalized gradient approximation (meta -GGA, mGGA) Räsänen, Pittalis and Proetto functional. Two doping sites, three oxidation states of the dopant and optional interstitial oxygen (O i) were considered. The calculations indicate that introduction of the dopant results in energy levels below conduction band, with strong contribution of Ta 5 d orbitals. The position of the levels depends strongly on the oxidation state of the dopant. Depending on the composition, two distinct electron traps with depths of 1.5–1.2 eV and 0.9–0.2 eV were revealed. Introduction of O i at proximity of the Ta dopant results in partial overlap of the Ta-related defect states with conduction band, which makes the traps very shallow, deteriorating the electron trapping properties. In some cases, shallow hole traps can also be attributed to the O i. The calculated traps structure is in good accord with the experimental data. Image 1 • Ta-doped cubic (bixbyite-type) lutetium oxide was analyzed using FP-LAPW/mGGA DFT calculations. • Two doping sites, three oxidation states of the dopant and optional interstitial oxygen were considered. • Two distinct electron traps (related to Ta 5 d orbitals) with depths of 1.5–1.2 eV and 0.9–0.2 eV were revealed. • Introduction of interstitial oxygen at proximity of the Ta dopant deteriorates the electron trapping properties. • The calculated traps structure is in good accord with experimental data. [ABSTRACT FROM AUTHOR]