scholarly journals Bayesian Optimization of Hubbard U’s for Investigating InGaN Superlattices

2021 ◽  
Vol 2 (3) ◽  
pp. 370-381
Author(s):  
Maxim N. Popov ◽  
Jürgen Spitaler ◽  
Lorenz Romaner ◽  
Natalia Bedoya-Martínez ◽  
René Hammer
Keyword(s):  
Electric Fields ◽  
Density Functional ◽  
Local Density ◽  
Bayesian Optimization ◽  
Hybrid Functional ◽  
Electronic Band ◽  
Functional Theory ◽  
Hubbard U ◽  
Electronic Band Structures ◽  
Standard Density

In this study, we undertake a Bayesian optimization of the Hubbard U parameters of wurtzite GaN and InN. The optimized Us are then tested within the Hubbard-corrected local density approximation (LDA+U) approach against standard density functional theory, as well as a hybrid functional (HSE06). We present the electronic band structures of wurtzite GaN, InN, and (1:1) InGaN superlattice. In addition, we demonstrate the outstanding performance of the new parametrization, when computing the internal electric-fields in a series of [InN]1–[GaN]n superlattices (n = 2–5) stacked up along the c-axis.

scholarly journals Intercalated architecture of MA2Z4 family layered van der Waals materials with emerging topological, magnetic and superconducting properties

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Lei Wang ◽  
Yongpeng Shi ◽  
Mingfeng Liu ◽  
Ao Zhang ◽  
Yi-Lun Hong ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Layer Structure ◽  
Atomic Layer ◽  
Type I ◽  
Hybrid Functional ◽  
Functional Theory ◽  
Valence Electrons ◽  
Nonmagnetic Metals ◽  
Standard Density

AbstractThe search for new two-dimensional monolayers with diverse electronic properties has attracted growing interest in recent years. Here, we present an approach to construct MA2Z4 monolayers with a septuple-atomic-layer structure, that is, intercalating a MoS2-type monolayer MZ2 into an InSe-type monolayer A2Z2. We illustrate this unique strategy by means of first-principles calculations, which not only reproduce the structures of MoSi2N4 and MnBi2Te4 that were already experimentally synthesized, but also predict 72 compounds that are thermodynamically and dynamically stable. Such an intercalated architecture significantly reconstructs the band structures of the constituents MZ2 and A2Z2, leading to diverse electronic properties for MA2Z4, which can be classified according to the total number of valence electrons. The systems with 32 and 34 valence electrons are mostly semiconductors. Whereas, those with 33 valence electrons can be nonmagnetic metals or ferromagnetic semiconductors. In particular, we find that, among the predicted compounds, (Ca,Sr)Ga2Te4 are topologically nontrivial by both the standard density functional theory and hybrid functional calculations. While VSi2P4 is a ferromagnetic semiconductor and TaSi2N4 is a type-I Ising superconductor. Moreover, WSi2P4 is a direct gap semiconductor with peculiar spin-valley properties, which are robust against interlayer interactions. Our study thus provides an effective way of designing septuple-atomic-layer MA2Z4 with unusual electronic properties to draw immediate experimental interest.

scholarly journals The Magnetic Band-Structures of Ordered PtxFe1−x, PtxCo1−x, and PtxNi1−x (x = 0.25, 0.50, and 0.75)

2020 ◽  
Vol 6 (4) ◽  
pp. 61
Author(s):  
Ian Shuttleworth
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
High Symmetry ◽  
Band Structures ◽  
Electronic Band ◽  
Functional Theory ◽  
Ni Alloys ◽  
Spin Polarized ◽  
Electronic Band Structures

The electronic band structures of the ordered L12 and L10 phases of the PtxM1−x (M = Fe, Co and Ni) alloys were investigated using spin-polarized density functional theory (DFT). The relative contributions of both itinerant (Stoner) and localized magnetism at the high-symmetry k-points were determined and discussed qualitatively. Significant directional effects were identified along the A and R directions of the L10 and L12 alloys, respectively, and are discussed in terms of charge channeling effects.

scholarly journals Evolution of Dirac Cone in Disclinated Graphene

2018 ◽  
Vol 57 (2) ◽  
pp. 137-142 ◽  
Author(s):  
M.A. Rozhkov ◽  
A.L. Kolesnikova ◽  
I. Hussainova ◽  
M.A. Kaliteevskii ◽  
T.S. Orlova ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Density Functional Theory ◽  
Band Structure ◽  
Density Functional ◽  
Md Simulation ◽  
Dirac Cone ◽  
Electronic Band ◽  
Functional Theory ◽  
Periodic Distribution ◽  
Electronic Band Structures

Abstract Graphene crystals, containing arrays of disclination defects, are modeled and their energies are calculated using molecular dynamics (MD) simulation technique. Two cases are analyzed in details: (i) pseudo-graphenes, which contain the alternating sign disclination ensembles and (ii) graphene with periodic distribution of disclination quadrupoles. Electronic band structures of disclinated graphene crystals are calculated in the framework of density functional theory (DFT) approach. The evolution of the Dirac cone and magnitude of band gap in the band structure reveal a dependence on the density of disclination quadrupoles and alternating sign disclinations. The electronic properties of graphene with disclination ensembles are discussed.

scholarly journals Machine learning the Hubbard U parameter in DFT+U using Bayesian optimization

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Maituo Yu ◽  
Shuyang Yang ◽  
Chunzhi Wu ◽  
Noa Marom
Keyword(s):  
Machine Learning ◽  
Transition Metal Oxides ◽  
Density Functional ◽  
Functional Results ◽  
Bayesian Optimization ◽  
Hybrid Functional ◽  
Band Structures ◽  
Local Exchange ◽  
Functional Theory ◽  
Exchange Correlation

AbstractWithin density functional theory (DFT), adding a Hubbard U correction can mitigate some of the deficiencies of local and semi-local exchange-correlation functionals, while maintaining computational efficiency. However, the accuracy of DFT+U largely depends on the chosen Hubbard U values. We propose an approach to determining the optimal U parameters for a given material by machine learning. The Bayesian optimization (BO) algorithm is used with an objective function formulated to reproduce the band structures produced by more accurate hybrid functionals. This approach is demonstrated for transition metal oxides, europium chalcogenides, and narrow-gap semiconductors. The band structures obtained using the BO U values are in agreement with hybrid functional results. Additionally, comparison to the linear response (LR) approach to determining U demonstrates that the BO method is superior.

FIRST-PRINCIPLES STUDIES ON THE ELECTRONIC STRUCTURE OF LuPd2Si2

2009 ◽  
Vol 23 (32) ◽  
pp. 5929-5934 ◽  
Author(s):  
T. JEONG
Keyword(s):  
Band Structure ◽  
First Principles ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Local Density ◽  
Spin Orbit Coupling ◽  
Electronic Band ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Structure Scheme

The electronic band structure of LuPd 2 Si 2 was studied based on the density functional theory within local density approximation and fully relativistic schemes. The Lu 4f states are completely filled and have flat bands around -5.0 eV. The fully relativistic band structure scheme shows that spin–orbit coupling splits the 4f states into two manifolds, the 4f7/2 and the 4f5/2 multiplet.

Systematic first principles calculations of the effects of stacking faults defects on the 4H-SiC band structure

2010 ◽  
Vol 1246 ◽  
Author(s):  
Massimo Camarda ◽  
pietro delugas ◽  
Andrea Canino ◽  
Andrea Severino ◽  
nicolo piluso ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Stacking Faults ◽  
Perfect Crystal ◽  
First Principles Calculations ◽  
Electronic Band ◽  
Functional Theory ◽  
Experimental Findings ◽  
Electronic Band Structures ◽  
Formation Energies

AbstractShockley-type Stacking faults (SSF) in hexagonal Silicon Carbide polytypes have received considerable attention in recent years since it has been found that these defects are responsible for the degradation of forward I-V characteristics in p-i-n diodes. In order to extend the knowledge on these kind of defects and theoretically support experimental findings (specifically, photoluminescence spectral analysis), we have determined the Kohn-Sham electronic band structures, along the closed path Γ-M-K-Γ, using density functional theory. We have also determined the energies of the SSFs with respect to the perfect crystal finding that the (35) and (44) SSFs have unexpectedly low formation energies, for this reason we could expect these two defects to be easily generated/expanded either during the growth or post-growth process steps.

Electronic band structures of Ge1−xSnx semiconductors: A first-principles density functional theory study

2013 ◽  
Vol 113 (6) ◽  
pp. 063517 ◽  
Author(s):  
Ming-Hsien Lee ◽  
Po-Liang Liu ◽  
Yung-An Hong ◽  
Yen-Ting Chou ◽  
Jia-Yang Hong ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Density Functional Theory Study ◽  
Band Structures ◽  
Electronic Band ◽  
Functional Theory ◽  
Electronic Band Structures

scholarly journals Comparative Analysis of DFTU, ACBN0, and Hybrid Functionals on the Spin Density of YTiO3 and SrRuO3+

2021 ◽  
Vol 11 (2) ◽  
pp. 616
Author(s):  
Francesca Menescardi ◽  
Davide Ceresoli
Keyword(s):  
Density Functional Theory ◽  
Quantum Theory ◽  
Spin Density ◽  
Density Functional ◽  
Functional Theory ◽  
Atomic Orbitals ◽  
Hubbard U ◽  
Density Map ◽  
Hybrid Functionals ◽  
Standard Density

We present a quantitative analysis of the theoretical spin density map of two ferromagnetic perovskites, YTiO3 and SrRuO3. We calculated the spin density using the standard density functional theory (DFT)+U method, where the Hubbard U correction is applied to the Ti and Ru ions, and with the pseudo-hybrid ACBN0 method, where the Hubbard U parameters are determined self-consistently. The ACBN0 calculations yielded a large value of the Hubbard U of the oxygen 2p orbitals. We also used the screened hybrid HSE06 functional, which is widely used to describe the electronic structure of oxides. We used the Quantum Theory of Atoms in Molecules (QTAIM) theory and integrated the spin density in the atomic basins instead of projecting on atomic orbitals. This way, our results can be compared to experimental reports as well as to other DFT calculations.

DENSITY FUNCTIONAL CALCULATION OF THE ELECTRONIC STRUCTURES OF SOME A5B6C7-TYPE CRYSTALS

2009 ◽  
Vol 23 (01) ◽  
pp. 97-104 ◽  
Author(s):  
HARUN AKKUS
Keyword(s):  
Density Functional ◽  
Density Functional Calculation ◽  
Generalized Gradient ◽  
Band Structures ◽  
Electronic Band ◽  
Functional Theory ◽  
Pseudopotential Theory ◽  
The Density Functional Theory ◽  
Indirect Band Gap ◽  
Electronic Band Structures

The electronic band structures of some A 5 B 6 C 7-type ternary compounds, BiSeI , BiSI , BiSCl , BiSBr , BiSeBr and SbSeBr , are investigated using the density functional theory and pseudopotential theory under the generalized gradient approximation (GGA). The electronic band structures obtained show that these crystals, except for BiSeI , have an indirect band gap.

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