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  1. Article ; Online: Density of States for Warped Energy Bands.

    Mecholsky, Nicholas A / Resca, Lorenzo / Pegg, Ian L / Fornari, Marco

    Scientific reports

    2016  Volume 6, Page(s) 22098

    Abstract: Warping of energy bands can affect the density of states (DOS) in ways that can be large or subtle ... explicit calculations of DOS and their effective masses for warped energy dispersions originally derived ... defined as pertaining to any multivariate energy function E(k) that does not admit a second-order ...

    Abstract Warping of energy bands can affect the density of states (DOS) in ways that can be large or subtle. Despite their potential for significant practical impacts on materials properties, these effects have not been rigorously demonstrated previously. Here we rectify this using an angular effective mass formalism that we have developed. To clarify the often confusing terminology in this field, "band warping" is precisely defined as pertaining to any multivariate energy function E(k) that does not admit a second-order differential at an isolated critical point in k-space, which we clearly distinguish from band non-parabolicity. We further describe band "corrugation" as a qualitative form of band warping that increasingly deviates from being twice differentiable at an isolated critical point. These features affect the density-of-states and other parameters ascribed to band warping in various ways. We demonstrate these effects, providing explicit calculations of DOS and their effective masses for warped energy dispersions originally derived by Kittel and others. Other physical and mathematical examples are provided to demonstrate fundamental distinctions that must be drawn between DOS contributions that originate from band warping and contributions that derive from band non-parabolicity. For some non-degenerate bands in thermoelectric materials, this may have profound consequences of practical interest.
    Language English
    Publishing date 2016-02-24
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 2615211-3
    ISSN 2045-2322 ; 2045-2322
    ISSN (online) 2045-2322
    ISSN 2045-2322
    DOI 10.1038/srep22098
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  2. Article ; Online: Computational Study of Elastic, Structural, Electronic, and Optical Properties of GaMF 3 (M = Be and Ge) Fluoroperovskites, Based on Density Functional Theory

    Hukam Khan / Mohammad Sohail / Nasir Rahman / Rajwali Khan / Mudasser Hussain / Asad Ullah / Aurangzeb Khan / Abed Alataway / Ahmed Z. Dewidar / Hosam O. Elansary / Kowiyou Yessoufou

    Molecules, Vol 27, Iss 16, p

    2022  Volume 5264

    Abstract: ... can be studied easily using their band gap energy. At high energy ranges, these substances demonstrate ... compound is insulating in nature. The involvement of various electronic states in band structures is ... calculated using the theory of the density of states. The different optical properties of these compounds ...

    Abstract This paper explains our first-principle computational investigation regarding the structural, optical, elastic, and electrical characteristics of gallium-based GaMF 3 (M = Be and Ge) perovskite-type (halide-perovskite) compounds. Our current computation is based on density functional theory (DFT) and is achieved with the help of the WIEN2k code. We used the Birch–Murnaghan equation for optimization; in both compounds, we found that both GaBeF 3 and GaGeF 3 compounds are structurally stable. For the computation of elastic characteristics, the IRelast package for calculating elastic constants (ECs) is utilized. These compounds are mechanically ductile, scratch-resistant, anisotropic, and mechanically stable, showing huge opposition to plastic strain. The modified Becke–Johnson (TB-mBJ) potential approximation method is used to calculate different physical characteristics and shows that GaGeF 3 behaves as a metal, whereas the GaBeF 3 compound is insulating in nature. The involvement of various electronic states in band structures is calculated using the theory of the density of states. The different optical properties of these compounds can be studied easily using their band gap energy. At high energy ranges, these substances demonstrate strong absorption. At low energies, the GaGeF 3 compound is transparent, while the GaBeF 3 compound is opaque to incoming photons. Investigation of the optical characteristics has led us to the conclusion that both GaGeF 3 and GaBeF 3 compounds can be used for high-frequency ultraviolet device applications. This computational work is considered to be the first time that we can study these compounds, which to our knowledge have not previously been experimentally validated.
    Keywords density functional theory ; fluoroperovskite ; optical properties ; structural properties ; electronic properties ; Organic chemistry ; QD241-441
    Subject code 540
    Language English
    Publishing date 2022-08-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article ; Online: Accurate prediction of the electronic properties of low-dimensional graphene derivatives using a screened hybrid density functional.

    Barone, Veronica / Hod, Oded / Peralta, Juan E / Scuseria, Gustavo E

    Accounts of chemical research

    2011  Volume 44, Issue 4, Page(s) 269–279

    Abstract: ... description of their band structure and density of states, their work function, and their magnetic ordering ... of these magnetic states in graphene nanoribbons can give rise to a half-metallic behavior when a transverse ... the correct prediction of the trigonal warping splitting in metallic nanotubes. The results predicted by HSE ...

    Abstract Over the last several years, low-dimensional graphene derivatives, such as carbon nanotubes and graphene nanoribbons, have played a central role in the pursuit of a plausible carbon-based nanotechnology. Their electronic properties can be either metallic or semiconducting depending purely on morphology, but predicting their electronic behavior has proven challenging. The combination of experimental efforts with modeling of these nanometer-scale structures has been instrumental in gaining insight into their physical and chemical properties and the processes involved at these scales. Particularly, approximations based on density functional theory have emerged as a successful computational tool for predicting the electronic structure of these materials. In this Account, we review our efforts in modeling graphitic nanostructures from first principles with hybrid density functionals, namely the Heyd-Scuseria-Ernzerhof (HSE) screened exchange hybrid and the hybrid meta-generalized functional of Tao, Perdew, Staroverov, and Scuseria (TPSSh). These functionals provide a powerful tool for quantitatively studying structure-property relations and the effects of external perturbations such as chemical substitutions, electric and magnetic fields, and mechanical deformations on the electronic and magnetic properties of these low-dimensional carbon materials. We show how HSE and TPSSh successfully predict the electronic properties of these materials, providing a good description of their band structure and density of states, their work function, and their magnetic ordering in the cases in which magnetism arises. Moreover, these approximations are capable of successfully predicting optical transitions (first and higher order) in both metallic and semiconducting single-walled carbon nanotubes of various chiralities and diameters with impressive accuracy. This versatility includes the correct prediction of the trigonal warping splitting in metallic nanotubes. The results predicted by HSE and TPSSh provide excellent agreement with existing photoluminescence and Rayleigh scattering spectroscopy experiments and Green's function-based methods for carbon nanotubes. This same methodology was utilized to predict the properties of other carbon nanomaterials, such as graphene nanoribbons. Graphene nanoribbons may be viewed as unrolled (and passivated) carbon nanotubes. However, the emergence of edges has a crucial impact on the electronic properties of graphene nanoribbons. Our calculations have shown that armchair nanoribbons are predicted to be nonmagnetic semiconductors with a band gap that oscillates with their width. In contrast, zigzag graphene nanoribbons are semiconducting with an electronic ground state that exhibits spin polarization localized at the edges of the carbon nanoribbon. The spatial symmetry of these magnetic states in graphene nanoribbons can give rise to a half-metallic behavior when a transverse external electric field is applied. Our work shows that these properties are enhanced upon different types of oxidation of the edges. We also discuss the properties of rectangular graphene flakes, which present spin polarization localized at the zigzag edges.
    Language English
    Publishing date 2011-04-19
    Publishing country United States
    Document type Journal Article
    ZDB-ID 1483291-4
    ISSN 1520-4898 ; 0001-4842
    ISSN (online) 1520-4898
    ISSN 0001-4842
    DOI 10.1021/ar100137c
    Database MEDical Literature Analysis and Retrieval System OnLINE

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