High Throughput Screening of Ternary Nitrides with Convolutional Neural Networks

The development of new materials is a core aspect of advancement in synthesis and application for industry. There is a vast number of possible chemical permutations of the basic elements that can be explored to synthesize materials that possess attractive catalytic, mechanical and electrical properties that may not be easily accessible to traditional experimental methods for various reasons, including cost and time considerations. Nitrides, as examples, require very stringent and precise conditions to successfully synthesize making their experimental exploration very slow. In this paper, we employ the use of machine learning algorithms to predict the bulk properties of Ternary Metal Nitrides (TMN), specifically their bulk modulus which is correlated with the hardness of the material. We were able to develop a consistent model with encouraging accuracy, that was able to predict the bulk moduli of materials that previously did not have computed values. The model was trained on $10^3$ ternary materials with known elastic properties and defined structures, and was able to predict the bulk modulus of $\thickapprox 1,000$ Ternary Metal Nitrides (TMNs) to $\thickapprox 80\%$ accuracy. This approach is orders of magnitude faster than the traditional computational approaches like density functional theory (DFT)\cite{dft-paper} which makes exploratory identification of materials with promising properties fast. We propose that such models be used to select interesting candidates for high throughput computation from first principles.Comment: 5 Pages, 5 Figures, 1 Tabl

First principles calculations of the thermoelectric properties of

Oxide based thermoelectric materials have gained considerable interest due to their abundance, low toxic nature and high temperature stability. In the present work, we report the thermoelectric properties of α-MnO2 and β-MnO2 investigated using the Density Functional Theory with a Hubbard correction as implemented in the VASP code. Our calculated band gaps 0.27 eV and 1.28 eV for β-MnO2 and α-MnO2, respectively, are in excellent agreement with the experimental values and hence demonstrate the importance of including a Hubbard correction (U) in studying the physical and electronic properties of manganese oxides. The calculated elastic constants obey the Born Huang elastic stability criteria and therefore indicate that the studied materials are mechanically stable. The computed phonon band structures and the vibrational density of states do not have imaginary frequencies throughout the Brillouin zone and hence is a clear indication of the dynamic stability of these materials. Our calculated lattice thermal conductivities (κL) show a strong anisotropic behaviour along the a and c directions. At room temperature, the results show that acoustic phonon modes contribute ~56.0(55.8)% in α-MnO2 and ~80.4(73.8)% in β-MnO2 to the total κL along the a(c) directions respectively. In addition, the thermoelectric transport coefficients; σ and S2σ display an anisotropic behaviour between a and c directions. We obtained higher power factors, i.e., (447)(435) μW/m K2 for α-MnO2 and (134)(225) μW/m K2 for β-MnO2 with hole doping concentration of 1020 cm−3 along the a(c) directions respectively compared to that of Bi2Te3 (40 μW/K2cm) at 300 K. This large thermoelectric power suggests that these materials may be potential candidates for thermoelectric applications. However, our calculated dimensionless figure of merit for β-MnO2 and α-MnO2 are quite small due to large values of lattice thermal conductivities. Our highest computed ZT values are 0.02 for β-MnO2 with hole doping concentration of 1021 cm−3, and 0.14 for α-MnO2 with electron carrier concentration of 1021 cm−3 at 800 K along the c-direction

Theoretical investigation of the thermoelectric properties of ACuO

The electronic, structural, mechanical, lattice dynamics and the electronic transport properties of ACuO2(A = K, Rb and Cs) are investigated using density functional theory. The calculated elastic constants and their related elastic moduli, phonon spectra and electronic transport properties of these compounds are reported here for the first time. The predicted structural parameters are in excellent agreement with the available experimental data. The obtained lattice thermal conductivities, κL, of ACuO2 (A = K, Rb and Cs) are found to display strong anisotropic features along the a, b and c directions. It is also found that the average room-temperature κL of CsCuO2 is lower than those of RbCuO2 and KCuO2, which is due to its smaller group velocities in the low frequency region i.e., 0 ~ 3 THz. Our calculations also show that the acoustic phonon modes contribute considerably to the total κL along the a and b directions. The electrical conductivity (σ) and electronic thermal conductivity (κel) of ACuO2 (A = K, Rb and Cs) show anisotropic features i.e., σ and κel along the c-axis is significantly larger than along the a and b-axes. Meanwhile, our obtained Seebeck coefficient (S) values are found to be 248, 110 and 91 μV/K for p-doped KCuO2, p-doped RbCuO2 and p-doped CsCuO2 respectively at 300 K along the b-direction. These S values are found to be of the same order of magnitude with that of well known thermoelectric (TE) material, Bi2Te3 (with S of 200 μV/K at 300 K) and the recently discovered metal oxide TE material, NaCo2O4 (with S of 100 μV/K at 300 K). However, our computed figure of merit (ZT) values of ACuO2 (A = K, Rb and Cs) are found to be very small as compared to known thermoelectric materials. For instance, our highest computed ZT value is 0.11 for p-type KCuO2 along the c-direction at 750 K, 0.15 for p-type RbCuO2 and 0.25 for p-type CsCuO2 along the a-direction at 800 K. These small ZT values are caused by large values of the lattice thermal conductivities

Effect of 3d transition metal substitutional dopants and adatoms on mono layer TcS2 ab initio insights

Obodo, Kingsley/0000-0002-1428-2761; Ouma, Cecil/0000-0001-7328-2254WOS: 000575753800009Within the spin polarized density functional theory formalism, the properties (structural, magnetic, electronic and optical) of transition metal (TM) substitutional doping as well as adsorption on monolayer TcS2 has been investigated. the TMs considered in this study were Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn. TM substitutional doping was found to be energetically favored under S-rich conditions compared to Tc-rich conditions. This suggests that it might be possible for substitutional doping to be realized experimentally. the calculated adsorption energies were negative in the case of Sc, Ti, V, Cr, Mn, Ni and Cu adsorption indicating the likelihood of adsorbing these TMs on mono layer TcS2. Both TM substitutional doping and adsorption were found to; induce a net magnetization, induce states within the band gap of the host and also modify the optical absorption spectra of TcS2. Magnetic ground states arising from transition metal doping and adsorption make these systems ideal candidates for magnetic and spintronic applications. Optical anisotropy was observed in the case of electric field parallel E parallel to(z) and perpendicular E perpendicular to(z) to the z-axis

Two-dimensional graphene-HfS(2) van der Waals heterostructure as electrode material for alkali-ion batteries

Poor electrical conductivity and large volume expansion during repeated charge and discharge is what has characterized many battery electrode materials in current use. This has led to 2D materials, specifically multi-layered 2D systems, being considered as alternatives. Among these 2D multi-layered systems are the graphene-based van der Waals heterostructures with transition metal di-chalcogenides (TMDCs) as one of the layers. Thus in this study, the graphene–hafnium disulphide (Gr–HfS2) system, has been investigated as a prototype Gr–TMDC system for application as a battery electrode. Density functional theory calculations indicate that Gr–HfS2 van der Waals heterostructure formation is energetically favoured. In order to probe its battery electrode application capability, Li, Na and K intercalants were introduced between the layers of the heterostructure. Li and K were found to be good intercalants as they had low diffusion barriers as well as a positive open circuit voltage. A comparison of bilayer graphene and bilayer HfS2 indicates that Gr–HfS2 is a favourable battery electrode syste