scholarly journals Ab initio theory of plasmonic superconductivity within the Eliashberg and density-functional formalisms

2020 ◽  
Vol 102 (21) ◽  
Author(s):  
A. Davydov ◽  
A. Sanna ◽  
C. Pellegrini ◽  
J. K. Dewhurst ◽  
S. Sharma ◽  
...  
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Ab Initio Theory

scholarly journals Ab Initio Theory of Magnetic Correlations in Itinerant Magnets

1997 ◽  
Vol 50 (6) ◽  
pp. 1083
Author(s):  
Michael F. Ling
Keyword(s):  
Magnetic Properties ◽  
Electronic Structure ◽  
Ab Initio ◽  
First Principles ◽  
Density Functional ◽  
Spin Fluctuation ◽  
Structure Theory ◽  
Magnetic Correlations ◽  
Ab Initio Theory ◽  
Quantitative Account

One of the challenging problems in modern magnetism is the description of the paramagnetic state because at finite temperatures the effect of spin fluctuation plays a fundamental role in altering the electronic structure. In magnetic metals, the magnetic properties are linked to the underlying spin-polarised electronic structure in a highly complex manner. In recent years, first-principles electronic structure theories based on the spin density functional (SDF) theory have been able to provide a quantitative account of many ground-state magnetic properties. In this article, the effect of spin fluctuation on the spin-polarised electronic structure and thus the magnetic properties will be discussed and its incorporation into ab initio calculations explained. If the magnetic and compositional ordering energies of magnetic metallic alloys are close, the compositional and magnetic correlations can profoundly influence each other. A theoretical formalism for treating these correlations within the framework of a first-principles electronic structure theory will be elaborated and the application to a number of magnetic alloys discussed and compared with experiments.

scholarly journals Ab initio theory of noble gas atoms in bcc transition metals

2018 ◽  
Vol 20 (25) ◽  
pp. 17048-17058 ◽  
Author(s):  
Chao Jiang ◽  
Yongfeng Zhang ◽  
Yipeng Gao ◽  
Jian Gan
Keyword(s):  
Density Functional Theory ◽  
Transition Metals ◽  
Ab Initio ◽  
Density Functional ◽  
Noble Gas ◽  
Functional Theory ◽  
Ab Initio Theory ◽  
Fundamental Understanding

Systematic ab initio calculations based on density functional theory have been performed to gain fundamental understanding of the interactions between noble gas atoms (He, Ne, Ar and Kr) and bcc transition metals in groups 5B (V, Nb and Ta), 6B (Cr, Mo and W) and 8B (Fe).

scholarly journals Ab initio theory of the negatively charged boron vacancy qubit in hexagonal boron nitride

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Viktor Ivády ◽  
Gergely Barcza ◽  
Gergő Thiering ◽  
Song Li ◽  
Hanen Hamdi ◽  
...  
Keyword(s):  
Boron Nitride ◽  
Ab Initio ◽  
Density Functional ◽  
Hexagonal Boron Nitride ◽  
Energy Levels ◽  
Quantum Bits ◽  
Density Matrix Renormalization ◽  
Ab Initio Theory ◽  
Optically Detected ◽  
Highly Correlated

AbstractHighly correlated orbitals coupled with phonons in two-dimension are identified for paramagnetic and optically active boron vacancy in hexagonal boron nitride by first principles methods which are responsible for recently observed optically detected magnetic resonance signal. Here, we report ab initio analysis of the correlated electronic structure of this center by density matrix renormalization group and Kohn-Sham density functional theory methods. By establishing the nature of the bright and dark states as well as the position of the energy levels, we provide a complete description of the magneto-optical properties and corresponding radiative and non-radiative routes which are responsible for the optical spin polarization and spin dependent luminescence of the defect. Our findings pave the way toward advancing the identification and characterization of room temperature quantum bits in two-dimensional solids.

Ab-Initio Theory of Defect Structure in a-Si iH

1986 ◽  
Vol 70 ◽  
Author(s):  
Yaneer Bar-Yam ◽  
J. D. Joannopoulos
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Atomic Number ◽  
Defect Structure ◽  
Density Functional ◽  
Functional Theory ◽  
Pseudopotential Theory ◽  
Recent Advances ◽  
Ab Initio Theory ◽  
Amorphous Si

ABSTRACTIt has recently become feasible that theory Will be able to predict the structure of solids “ab-initio”, using only the atomic number of the constituent atoms as input. This is based on recent advances in density-functional theory and pseudopotential theory. A simple physical introduction of the concepts underlying these theories is presented. Special emphasis is given to examining the structure and effective correlation energies of defects in amorphous Si.

A Combined ab initio and Density Functional Study of the Electronic Structure of Thymine and 2-Thiothymine Radicals

2003 ◽  
Vol 68 (12) ◽  
pp. 2322-2334 ◽  
Author(s):  
Robert Vianello ◽  
Zvonimir B. Maksić
Keyword(s):  
Ab Initio ◽  
Spin Density ◽  
Density Functional ◽  
Radical Cations ◽  
Functional Study ◽  
Theory Approach ◽  
Functional Theory ◽  
Adiabatic Ionization Potential ◽  
Highest Occupied Molecular Orbital ◽  
Positively Charged

The electronic and energetic properties of thymine (1) and 2-thiothymine (2) and their neutral and positively charged radicals are considered by a combined ab initio and density functional theory approach. It is conclusively shown that ionization of 1 and 2 greatly facilitates deprotonation of the formed radical cations thus making the proton transfer between charged and neutral precursor species thermodynamically favourable. The adiabatic ionization potential of 1 and 2 are analysed. It appears that ADIP(1) is larger than ADIP(2) by 10 kcal/mol, because of greater stability of the highest occupied molecular orbital (HOMO) of the former. It is also shown beyond any doubt that the spin density in neutral and cationic radical of 2 is almost exclusively placed on the σ-3p AO of sulfur implying that these two systems represent rather rare sigma-radicals. In contrast, the spin density of radicals of 1 is distributed over their π-network.

scholarly journals Phonons in Short-Period GaN/AlN Superlattices: Group-Theoretical Analysis, Ab initio Calculations, and Raman Spectra

Nanomaterials ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 286
Author(s):  
Valery Davydov ◽  
Evgenii Roginskii ◽  
Yuri Kitaev ◽  
Alexander Smirnov ◽  
Ilya Eliseyev ◽  
...  
Keyword(s):  
Theoretical Analysis ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Raman Spectra ◽  
Density Functional ◽  
Structural Characteristics ◽  
Vibrational Modes ◽  
Phonon Modes ◽  
Short Period ◽  
Group Theoretical Analysis

We report the results of experimental and theoretical studies of phonon modes in GaN/AlN superlattices (SLs) with a period of several atomic layers, grown by submonolayer digital plasma-assisted molecular-beam epitaxy, which have a great potential for use in quantum and stress engineering. Using detailed group-theoretical analysis, the genesis of the SL vibrational modes from the modes of bulk AlN and GaN crystals is established. Ab initio calculations in the framework of the density functional theory, aimed at studying the phonon states, are performed for SLs with both equal and unequal layer thicknesses. The frequencies of the vibrational modes are calculated, and atomic displacement patterns are obtained. Raman spectra are calculated and compared with the experimental ones. The results of the ab initio calculations are in good agreement with the experimental Raman spectra and the results of the group-theoretical analysis. As a result of comprehensive studies, the correlations between the parameters of acoustic and optical phonons and the structure of SLs are obtained. This opens up new possibilities for the analysis of the structural characteristics of short-period GaN/AlN SLs using Raman spectroscopy. The results obtained can be used to optimize the growth technologies aimed to form structurally perfect short-period GaN/AlN SLs.

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