Two kinds of generalized gradient representations for generalized Birkhoff system

The generalized gradient approximation (GGA) often fails to correctly describe the electronic structure and thermochemistry of transition metal oxides and is commonly improved using an inexpensive correction term with a scaling parameter U. We tune U to reproduce experimental vanadium oxide redox energetics with a localized basis and a GGA functional. We find the value for U to be significantly lower than what is generally reported with plane-wave bases, with the uncorrected GGA results being in reasonable agreement with experiments. We use this computational setup to calculate interstitial and substitutional <a>insertion energies of main group metals in vanadium pentoxide</a> and find <a>interstitial doping to be thermodynamically favored</a>.

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Ab initio calculation on the Optical Properties of AA- Stacked two dimensional Graphene, Silicene, Germanene, and Stanene

International Journal of Computational Physics Series ◽

10.29167/a1i1p46-50 ◽

2018 ◽

Vol 1 (1) ◽

pp. 46-50

Author(s):

Rita John ◽

Benita Merlin

Keyword(s):

Optical Properties ◽

Band Structure ◽

Density Functional ◽

Electronic Band Structure ◽

Complex Refractive Index ◽

Single Layer ◽

Generalized Gradient ◽

Electronic Band ◽

Wide Range ◽

Optical Region

In this study, we have analyzed the electronic band structure and optical properties of AA-stacked bilayer graphene and its 2D analogues and compared the results with single layers. The calculations have been done using Density Functional Theory with Generalized Gradient Approximation as exchange correlation potential as in CASTEP. The study on electronic band structure shows the splitting of valence and conduction bands. A band gap of 0.342eV in graphene and an infinitesimally small gap in other 2D materials are generated. Similar to a single layer, AA-stacked bilayer materials also exhibit excellent optical properties throughout the optical region from infrared to ultraviolet. Optical properties are studied along both parallel (||) and perpendicular ( ) polarization directions. The complex dielectric function (ε) and the complex refractive index (N) are calculated. The calculated values of ε and N enable us to analyze optical absorption, reflectivity, conductivity, and the electron loss function. Inferences from the study of optical properties are presented. In general the optical properties are found to be enhanced compared to its corresponding single layer. The further study brings out greater inferences towards their direct application in the optical industry through a wide range of the optical spectrum.

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Performance of SCAN Meta-GGA Functionals on Nonlinear Mechanics of Graphene-Like g-SiC

Crystals ◽

10.3390/cryst11020120 ◽

2021 ◽

Vol 11 (2) ◽

pp. 120

Author(s):

Qing Peng

Keyword(s):

Mechanical Properties ◽

Density Functional ◽

Large Strains ◽

Two Dimensional ◽

Nonlinear Mechanics ◽

Generalized Gradient ◽

Mechanics Of Materials ◽

Nonlinear Mechanical ◽

Direct Band ◽

Simulations And Modeling

Although meta-generalized-gradient approximations (meta-GGAs) are believed potentially the most accurate among the efficient first-principles calculations, the performance has not been accessed on the nonlinear mechanical properties of two-dimensional nanomaterials. Graphene, like two-dimensional silicon carbide g-SiC, has a wide direct band-gap with applications in high-power electronics and solar energy. Taken g-SiC as a paradigm, we have investigated the performance of meta-GGA functionals on the nonlinear mechanical properties under large strains, both compressive and tensile, along three deformation modes using Strongly Constrained and Appropriately Normed Semilocal Density Functional (SCAN) as an example. A close comparison suggests that the nonlinear mechanics predicted from SCAN are very similar to that of Perdew-Burke-Ernzerhof (PBE) formulated functional, a standard Density Functional Theory (DFT) functional. The improvement from SCAN calculation over PBE calculation is minor, despite the considerable increase of computing demand. This study could be helpful in selection of density functionals in simulations and modeling of mechanics of materials.

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MCML : Combining physical constraints with experimental data for a multi‐purpose meta‐generalized gradient approximation

Journal of Computational Chemistry ◽

10.1002/jcc.26732 ◽

2021 ◽

Author(s):

Kristopher Brown ◽

Yasheng Maimaiti ◽

Kai Trepte ◽

Thomas Bligaard ◽

Johannes Voss

Keyword(s):

Experimental Data ◽

Generalized Gradient ◽

Physical Constraints ◽

Generalized Gradient Approximation

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Dissociation of dinitrogen on iron clusters: A detailed study of the Fe16 + N2 case.

Physical Chemistry Chemical Physics ◽

10.1039/d0cp05427e ◽

2020 ◽

Author(s):

Bole Chen ◽

Gennady L. Gutsev ◽

Weiguo Sun ◽

Xiao-Yu Kuang ◽

Cheng Lu ◽

...

Keyword(s):

Density Functional Theory ◽

Density Functional ◽

Basis Set ◽

Generalized Gradient ◽

Functional Theory ◽

Iron Clusters ◽

Generalized Gradient Approximation

The coalescence of two Fe8N as well as the structure of the Fe16N2 cluster were studied using density functional theory with the generalized gradient approximation and a basis set of...

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Calculation of Band Offsets of Mg(OH)2-Based Heterostructures

Electronic Materials ◽

10.3390/electronicmat2030019 ◽

2021 ◽

Vol 2 (3) ◽

pp. 274-283

Author(s):

Masaya Ichimura

Keyword(s):

Solar Cells ◽

Valence Band ◽

Dye Sensitized Solar Cells ◽

Band Alignment ◽

First Principles Calculation ◽

Band Edge ◽

Level Energy ◽

Type I ◽

Valence Band Edge ◽

Generalized Gradient

The band alignment of Mg(OH)2-based heterostructures is investigated based on first-principles calculation. (111)-MgO/(0001)-Mg(OH)2 and (0001)-wurtzite ZnO/(0001)-Mg(OH)2 heterostructures are considered. The O 2s level energy is obtained for each O atom in the heterostructure supercell, and the band edge energies are evaluated following the procedure of the core-level spectroscopy. The calculation is based on the generalized gradient approximation with the on-site Coulomb interaction parameter U considered for Zn. For MgO/Mg(OH)2, the band alignment is of type II, and the valence band edge of MgO is higher by 1.6 eV than that of Mg(OH)2. For ZnO/Mg(OH)2, the band alignment is of type I, and the valence band edge of ZnO is higher by 0.5 eV than that of Mg(OH)2. Assuming the transitivity rule, it is expected that Mg(OH)2 can be used for certain types of heterostructure solar cells and dye-sensitized solar cells to improve the performance.

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Thermal Properties of Divalent Metal Oxides: CaO as a Prototype

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.209.190 ◽

2013 ◽

Vol 209 ◽

pp. 190-193

Author(s):

Nisarg K. Bhatt ◽

Brijmohan Y. Thakore ◽

P.R. Vyas ◽

A.Y. Vahora ◽

Asvin R. Jani

Keyword(s):

Density Functional ◽

Tight Binding ◽

Mean Field ◽

Field Potential ◽

Theoretical Data ◽

Test Case ◽

Generalized Gradient ◽

Core Electrons ◽

Vibrational Free Energy ◽

Semi Empirical

Commonly employed quasiharmonic approximation (QHA) is inadequate to account for intrinsic anharmonism such as phonon-phonon interaction, vacancy contribution, etc. Though anharmonic contributions are important at high temperatures and low pressure, complete ab initio calculations are scanty due largely to laborious computational requirements. Nevertheless, some simple semi-empirical schemes can be used effectively to incorporate the anharmonism. In this regards, in the present study we have proposed a simple computational scheme to include the effect of vacancy directly into the description within the mean-field potential approach, which calculates vibrational free energy of ions. Validity of the scheme is verified by taking calcium oxide as a test case. Equilibrium properties at (T,P) = (0,0) condition is obtained within the tight-binding second-moment approximation (TB-SMA), whose parameters were determined through first principles density functional theory. Kohn-Sham equations for core electrons were solved using ultrasoft plane-wave pseudopotential employing the generalized gradient approximation for exchange and correlation. Present findings for thermal expansion and high-T EOS clearly show perceptible improvement over the case when vacancy contribution was not included. Some related thermodynamic properties are also calculated and compared with the available experimental and theoretical data.

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Study of thermo-elastic and lattice dynamics properties of half-Heusler compounds XMgAl (X = Li, Na) by computational investigations

Modern Physics Letters B ◽

10.1142/s0217984919500933 ◽

2019 ◽

Vol 33 (08) ◽

pp. 1950093 ◽

Cited By ~ 1

Author(s):

A. Afaq ◽

Abu Bakar ◽

M. Rizwan ◽

M. Aftab Fareed ◽

H. Bushra Munir ◽

...

Keyword(s):

Debye Temperature ◽

Elastic Constants ◽

Density Functional ◽

Phonon Dispersion ◽

Dynamic Properties ◽

Mechanical Parameters ◽

Heusler Compounds ◽

Generalized Gradient ◽

Text Type ◽

Quantum Espresso

In this study, thermo-elastic and lattice dynamic properties of XMgAl (X = Li, Na) half-Heusler compounds are investigated using density functional theory implemented in WIEN2k and Quantum ESPRESSO codes. Generalized gradient approximation (GGA) as an exchange correlation function has been used in Kohn–Sham equations. Firstly, the structure of these Heusler compounds is optimized and then these optimized parameters are used to find three elastic constants [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text] type structures. Three elastic constants are then used to determine different elastic moduli like bulk modulus, shear modulus, Young’s modulus and other mechanical parameters like Pugh’s ratio, Poisson’s ratio, anisotropic ratio, sound velocities, Debye temperature and melting temperature. On behalf of these mechanical parameters, the brittle/ductile nature and isotropic/anisotropic behavior of the materials has been studied. Different regions of vibrational modes in the materials are also discussed on behalf of Debye temperature calculations. The vibrational properties of the half-Heusler compounds are computed using Martins–Troullier pseudo potentials implemented in Quantum ESPRESSO. The phonon dispersion curves and phonon density of states in first Brillion zone are obtained and discussed. Reststrahlen band of LiMgAl is found greater than NaMgAl.

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