Browsing by Author "Kvashnin, Alexander G."

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    Electronic Properties of Functionalized Diamanes for Field-Emission Displays
    (Amerian Chemical Society, 2023) Tantardini, Christian; Kvashnin, Alexander G.; Azizi, Maryam; Gonze, Xavier; Gatti, Carlo; Altalhi, Tariq; Yakobson, Boris I.
    Ultrathin diamond films, or diamanes, are promising quasi-2D materials that are characterized by high stiffness, extreme wear resistance, high thermal conductivity, and chemical stability. Surface functionalization of multilayer graphene with different stackings of layers could be an interesting opportunity to induce proper electronic properties into diamanes. Combination of these electronic properties together with extraordinary mechanical ones will lead to their applications as field-emission displays substituting original devices with light-emitting diodes or organic light-emitting diodes. In the present study, we focus on the electronic properties of fluorinated and hydrogenated diamanes with (111), (110), (0001), (101̅0), and (2̅110) crystallographic orientations of surfaces of various thicknesses by using first-principles calculations and Bader analysis of electron density. We see that fluorine induces an occupied surface electronic state, while hydrogen modifies the occupied bulk state and also induces unoccupied surface states. Furthermore, a lower number of layers is necessary for hydrogenated diamanes to achieve the convergence of the work function in comparison with fluorinated diamanes, with the exception of fluorinated (110) and (2̅110) films that achieve rapid convergence and have the same behavior as other hydrogenated surfaces. This induces a modification of the work function with an increase of the number of layers that makes hydrogenated (2̅110) diamanes the most suitable surface for field-emission displays, better than the fluorinated counterparts. In addition, a quasi-quantitative descriptor of surface dipole moment based on the Tantardini–Oganov electronegativity scale is introduced as the average of bond dipole moments between the surface atoms. This new fundamental descriptor is capable of predicting a priori the bond dipole moment and may be considered as a new useful feature for crystal structure prediction based on artificial intelligence.
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    Material hardness descriptor derived by symbolic regression
    (Elsevier, 2024) Tantardini, Christian; Zakaryan, Hayk A.; Han, Zhong-Kang; Altalhi, Tariq; Levchenko, Sergey V.; Kvashnin, Alexander G.; Yakobson, Boris I.
    Hardness is a materials’ property with implications in several industrial fields, including oil and gas, manufacturing, and others. However, the relationship between this macroscale property and atomic (i.e., microscale) properties is unknown and in the last decade several models have unsuccessfully tried to correlate them in a wide range of chemical space. The understanding of such relationship is of fundamental importance for discovery of harder materials with specific characteristics to be employed in a wide range of fields. In this work, we have found a physical descriptor for Vickers hardness using a symbolic-regression artificial-intelligence approach based on compressed sensing. SISSO (Sure Independence Screening plus Sparsifying Operator) is an artificial-intelligence algorithm used for discovering simple and interpretable predictive models. It performs feature selection from up to billions of candidates obtained from several primary features by applying a set of mathematical operators. The resulting sparse SISSO model accurately describes the target property (i.e., Vickers hardness) with minimal complexity. We have considered the experimental values of hardness for binary, ternary, and quaternary transition-metal borides, carbides, nitrides, carbonitrides, carboborides, and boronitrides of 61 materials, on which the fitting was performed.. The found descriptor is a non-linear function of the microscopic properties, with the most significant contribution being from a combination of Voigt-averaged bulk modulus, Poisson’s ratio, and Reuss-averaged shear modulus. Results of high-throughput screening of 635 candidate materials using the found descriptor suggest the enhancement of material’s hardness through mixing with harder yet metastable structures (e.g., metastable VN, TaN, ReN2, Cr3N4, and ZrB6 all exhibit high hardness).
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    Theoretical study of adsorption properties and CO oxidation reaction on surfaces of higher tungsten boride
    (Springer Nature, 2024) Radina, Aleksandra D.; Baidyshev, Viktor S.; Chepkasov, Ilya V.; Matsokin, Nikita A.; Altalhi, Tariq; Yakobson, Boris I.; Kvashnin, Alexander G.
    Most modern catalysts are based on precious metals and rear-earth elements, making some of organic synthesis reactions economically insolvent. Density functional theory calculations are used here to describe several differently oriented surfaces of the higher tungsten boride WB5-x, together with their catalytic activity for the CO oxidation reaction. Based on our findings, WB5-x appears to be an efficient alternative catalyst for CO oxidation. Calculated surface energies allow the use of the Wulff construction to determine the equilibrium shape of WB5-x particles. It is found that the (010) and (101) facets terminated by boron and tungsten, respectively, are the most exposed surfaces for which the adsorption of different gaseous agents (CO, CO2, H2, N2, O2, NO, NO2, H2O, NH3, SO2) is evaluated to reveal promising prospects for applications. CO oxidation on B-rich (010) and W-rich (101) surfaces is further investigated by analyzing the charge redistribution during the adsorption of CO and O2 molecules. It is found that CO oxidation has relatively low energy barriers. The implications of the present results, the effects of WB5-x on CO oxidation and potential application in the automotive, chemical, and mining industries are discussed.