scholarly journals Computational density-functional approaches on finite-size and guest-lattice effects in CO2@sII clathrate hydrate

2021 ◽  
Vol 154 (4) ◽  
pp. 044301
Author(s):  
Adriana Cabrera-Ramírez ◽  
Raquel Yanes-Rodríguez ◽  
Rita Prosmiti
Keyword(s):  
Density Functional ◽  
Finite Size ◽  
Clathrate Hydrate ◽  
Lattice Effects

scholarly journals Density-functional approximations on CO2@sI clathrate hydrate interactions

2017 ◽  
Vol 875 ◽  
pp. 112015
Author(s):  
Daniel J. Arismendi-Arrieta ◽  
Álvaro Valdés ◽  
Rita Prosmiti
Keyword(s):  
Density Functional ◽  
Clathrate Hydrate

Study on the optical spectra of the oxygen vacancy in ZnWO4 crystal

2021 ◽  
pp. 2150471
Author(s):  
Gaiping Lian ◽  
Tingyu Liu ◽  
Le Yu
Keyword(s):  
Oxygen Vacancy ◽  
Density Functional ◽  
Defect Formation ◽  
Finite Size ◽  
Optical Spectra ◽  
Functional Method ◽  
Hybrid Functional ◽  
Electron Phonon Coupling ◽  
Correction Scheme ◽  
The Density Functional Theory

ZnWO4 is easy to color, which will reduce the luminous efficiency of the crystal and limit the application of the crystal. In order to study the origin of the color in the crystal, in this paper, the effects of the oxygen vacancy on the optical properties for the ZnWO4 crystal have been studied based on the density functional theory (DFT). The hybrid functional method (HSE) and the finite-size correction scheme (FNV) are used to correct the band edge problem and eliminate the artificial interaction of the charged defects, respectively. On the basis of the corrected defect formation energy, we obtain the optical spectra of the [Formula: see text] and [Formula: see text] centers containing electron-phonon coupling. The calculated absorption and luminescence peaks are at 2.54 eV and 0.79 eV for the [Formula: see text] center and at 2.98 eV and 1.09 eV for the [Formula: see text] center, respectively. The calculated absorption band of the [Formula: see text] center is close to the experimental value of 2.48 eV (500 nm), so we speculate that the coloring of the ZnWO4 crystal is related to the [Formula: see text] center. Meanwhile, the existence of oxygen vacancy makes ZnWO4 crystal to have self-absorption and to increase decay time, which greatly affects the scintillation properties of the crystal.

scholarly journals Electronic properties of the coronene series from thermally-assisted-occupation density functional theory

RSC Advances ◽  
2018 ◽  
Vol 8 (60) ◽  
pp. 34350-34358 ◽  
Author(s):  
Chia-Nan Yeh ◽  
Can Wu ◽  
Haibin Su ◽  
Jeng-Da Chai
Keyword(s):  
Density Functional Theory ◽  
Electronic Properties ◽  
Density Functional ◽  
Finite Size ◽  
Comprehensive Understanding ◽  
Functional Theory ◽  
Graphene Flakes

To fully utilize the great potential of graphene in electronics, a comprehensive understanding of the electronic properties of finite-size graphene flakes is essential.

scholarly journals Geometries and Electronic States of Divacancy Defect in Finite-Size Hexagonal Graphene Flakes

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
Lili Liu ◽  
Shimou Chen
Keyword(s):  
Ground State ◽  
First Principles ◽  
Density Functional ◽  
Singlet State ◽  
Tight Binding ◽  
Finite Size ◽  
Electronic States ◽  
Closed Shell ◽  
Graphene Flakes ◽  
Self Consistent

The geometries and electronic properties of divacancies with two kinds of structures were investigated by the first-principles (U) B3LYP/STO-3G and self-consistent-charge density-functional tight-binding (SCC-DFTB) method. Different from the reported understanding of these properties of divacancy in graphene and carbon nanotubes, it was found that the ground state of the divacancy with 585 configurations is closed shell singlet state and much more stable than the 555777 configurations in the smaller graphene flakes, which is preferred to triplet state. But when the sizes of the graphene become larger, the 555777 defects will be more stable. In addition, the spin density properties of the both configurations are studied in this paper.

Picosecond Electronic and Structural Dynamics in Photo-excited Monolayer MoSe2

MRS Advances ◽  
2018 ◽  
Vol 3 (6-7) ◽  
pp. 391-396
Author(s):  
Lindsay Bassman ◽  
Aravind Krishnamoorthy ◽  
Aiichiro Nakano ◽  
Rajiv K. Kalia ◽  
Hiroyuki Kumazoe ◽  
...  
Keyword(s):  
Structural Dynamics ◽  
Material Properties ◽  
Density Functional ◽  
Electronic Excitation ◽  
Field Effect Transistors ◽  
Finite Size ◽  
Optical Control ◽  
Quantum Molecular Dynamics ◽  
Strong Light ◽  
Dynamics Simulations

Monolayers of semiconducting transitional metal dichalcogenides (TMDC) are emerging as strong candidate materials for next generation electronic and optoelectronic devices, with applications in field-effect transistors, valleytronics, and photovoltaics. Prior studies have demonstrated strong light-matter interactions in these materials, suggesting optical control of material properties as a promising route for their functionalization. However, the electronic and structural dynamics in response to electronic excitation have not yet been fully elucidated. In this work, we use non-adiabatic quantum molecular dynamics simulations based on time-dependent density functional theory to study lattice dynamics of a model TMDC monolayer of MoSe2 after electronic excitation. The simulation results show rapid, sub-picosecond lattice response, as well as finite-size effects. Understanding the sub-picosecond atomic dynamics is important for the realization of optical control of the material properties of monolayer TMDCs, which is a hopeful, straightforward tactic for functionalizing these materials.

scholarly journals Dynamical Effective Field Model for Interacting Ferrofluids: I. Derivations for homogeneous, inhomogeneous, and polydisperse cases

2021 ◽  
Author(s):  
Angbo Fang
Keyword(s):  
Information Transfer ◽  
Density Functional ◽  
Field Model ◽  
Finite Size ◽  
Effective Field ◽  
Theoretical Ground ◽  
Local Magnetization ◽  
Relaxation Equation ◽  
Magnetization Relaxation ◽  
Demagnetizing Field

Abstract Quite recently I have proposed a nonperturbative dynamical effective field model (DEFM) to quantitatively describe the dynamics of interacting ferrofluids. Its predictions compare very well with the results from Brownian dynamics simulations. In this paper I put the DEFM on firm theoretical ground by deriving it within the framework of dynamical density functional theory (DDFT), taking into account nonadiabatic effects. The DEFM is generalized to inhomogeneous finite-size samples for which the macroscopic and mesoscopic scale separation is nontrivial due to the presence of long-range dipole-dipole interactions. The demagnetizing field naturally emerges from microscopic considerations and is consistently accounted for. The resulting mesoscopic dynamics only involves macroscopically local quantities such as local magnetization and Maxwell field. Nevertheless, the local demagnetizing field essentially couples to magnetization at distant macroscopic locations. Thus, a two-scale parallel algorithm, involving information transfer between different macroscopic locations, can be applied to fully solve the dynamics in an inhomogeneous sample. I also derive the DEFM for polydisperse ferrofluids, in which different species can be strongly coupled to each other dynamically. I discuss the underlying assumptions in obtaining a thermodynamically consistent polydisperse magnetization relaxation equation, which is of the same generic form as that for monodisperse ferrofluids. The theoretical advances presented in this paper are important for both qualitative understanding and quantitative modeling of the dynamics of ferrofluids and other dipolar systems.

First-principles study on the optical spectra of ZrO2 crystal with oxygen vacancy

2019 ◽  
Vol 33 (31) ◽  
pp. 1950372
Author(s):  
Rui Guo ◽  
Tingyu Liu ◽  
Yazhou Lu ◽  
Qiuyue Li ◽  
Xuping Jiao ◽  
...  
Keyword(s):  
Oxygen Vacancy ◽  
Density Functional ◽  
Defect Formation ◽  
Finite Size ◽  
Optical Spectra ◽  
Photocatalytic Ability ◽  
Luminescence Peak ◽  
Electron Phonon Coupling ◽  
Correction Scheme ◽  
F Center

In this paper, we present the optical spectra of the ZrO2 crystal containing oxygen vacancy based on the Density Functional Theory (DFT). The finite-size correction scheme (FNV) is employed to eliminate the artificial interactions and correct the defect formation energy of oxygen vacancies with three different charges (0, +1, +2). Besides, we use hybrid density functionals to relieve the band edge problem. Finally, we obtain the optical spectra for the F center and F[Formula: see text] center containing the electron–phonon coupling. The absorption peak of F center of threefold coordinate oxygen vacancy (V[Formula: see text]) near 446 nm (2.78 eV) agrees well with the experimental value (2.83 eV), which can enhance the visible light photocatalytic ability of ZrO2. The luminescence peak of the F[Formula: see text] center of fourfold coordinate oxygen vacancy (V[Formula: see text]) is 561 nm (2.21 eV), which is close to the experimental value (2.5 eV).

scholarly journals Electronic and Optical Properties of the Narrowest Armchair Graphene Nanoribbons Studied by Density Functional Methods

2016 ◽  
Vol 69 (9) ◽  
pp. 960 ◽  
Author(s):  
Chia-Nan Yeh ◽  
Pei-Yin Lee ◽  
Jeng-Da Chai
Keyword(s):  
Density Functional Theory ◽  
Optical Properties ◽  
Ground State ◽  
Density Functional ◽  
Graphene Nanoribbons ◽  
Finite Size ◽  
Functional Theory ◽  
Electronic And Optical Properties ◽  
Armchair Graphene Nanoribbons ◽  
Armchair Graphene

In the present study, a series of planar poly(p-phenylene) (PPP) oligomers with n phenyl rings (n = 1–20), designated as n-PP, are taken as finite-size models of the narrowest armchair graphene nanoribbons with hydrogen passivation. The singlet-triplet energy gap, vertical ionization potential, vertical electron affinity, fundamental gap, optical gap, and exciton binding energy of n-PP are calculated using Kohn-Sham density functional theory and time-dependent density functional theory with various exchange-correlation density functionals. The ground state of n-PP is shown to be singlet for all the chain lengths studied. In contrast to the lowest singlet state (i.e., the ground state) of n-PP, the lowest triplet state of n-PP and the ground states of the cation and anion of n-PP are found to exhibit some multi-reference character. Overall, the electronic and optical properties of n-PP obtained from the ωB97 and ωB97X functionals are in excellent agreement with the available experimental data.

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