Kobaissy, Ali Al-Hadi I.Ayoub, GeorgesShehadeh, Mutasem
17页
查看更多>>摘要：In this work, a physically based model accounting for grain-to-grain interaction and grain refinement mechanisms is proposed to predict the anisotropic mechanical response and the texture evolution in ECAPed Mg-3Al1Zn. The proposed model couples two approaches: crystal plasticity (CP), including twinning, and continuum dislocation dynamics (CDD). A grain refinement mechanism is also integrated into the model in order to predict the formation of refined grains during severe plastic deformation. A robust parameter identification method is proposed, in which experimentally reported process parameters are calibrated to fit the simulated mechanical behavior, texture evolution, and deformation systems-related activities. The anisotropic behavior evolution of the Mg-3Al-1Zn hot-rolled plate is examined by predicting the mechanical behavior, dislocation evolution, and slip/twin systems activities of the ECAPed material. The coupled CP-CDD model predicts grain size reduction with an average grain size which is in agreement with the experimentally measured values. Furthermore, the model generated textures are in accordance with those reported in the literature. Finally, a good agreement between the experimental and predicted true tensile stress-strain curves up to the ultimate tensile strength for both routes 4A and 4 K along extrusion and flow directions was found.
查看更多>>摘要：We study the electronic properties of heterostructures based on monolayer black phosphorus (BP) and two types of borophene (HBoro and Boro delta). The contact between BP and borophene results in the disappearance of Schottky barriers, indicates the metallization of BP. The BP/HBoro forms an n-type Schottky contact and BP/ Boro & UDelta; forms a p-type Schottky contact between the channels and electrodes. The edge modification of BP also affects the Schottky contact type and Schottky barrier heights. Moreover, it is found that the gate voltage can not only effectively modulate the Schottky barrier height but also change the Schottky contact type of BP/borophene structures. The ohmic contact can be achieved at some certain gate voltage. The results provide a promising route to design and fabricate tunable devices based on edge modified BP with borophene electrodes.
查看更多>>摘要：The BoltzWann code uses the first-principles density-functional theory to calculate the material's response to an electric field and temperature gradient within the constant relaxation time approximation. We extend this code to include the response of the system to a magnetic field. The carrier dynamic is described by the semi-classical Boltzmann transport equation. This equation is solved in the presence of an external magnetic field within the constant relaxation time approximation and using the Jones-Zener expansion. This is done through a Wannier interpolation of the density functional theory bands using the Boltzwann code, followed by the computation of group velocities and effective masses leading to the energy-dependent transport function. This work leads to a generalized method for the calculation of thermomagnetic properties of materials. The results are validated by comparison to the analytical solutions of the thermomagnetic properties for several simple energy dispersion types and close agreements at moderate computational costs are achieved. This method can pave the path for the discovery of materials with potentially high thermomagnetic power factor.
查看更多>>摘要：Inevitably, all crystalline materials will contain imperfections that have the ability to modify the properties of the host material. Key to the development of advanced materials is the ability to predict the concentrations of different defects in any given environmental conditions and how the change in the defect population alters the material's properties. Modern first principles atomistic simulation techniques, such as density functional theory (DFT), are now widely employed for the simulation of point defects, however, to develop true insight into a material's defect chemistry, it is essential to link the energies calculated to thermodynamic variables that fully describe its operating conditions. The Defect Analysis Package (DefAP), an open-source Python code, has been designed to fulfil this role. The primary function of the package is to predict the concentrations of defects in materials as a function of key thermodynamic variables, such as temperature and availability of different species, expressed through chemical potentials. Through simple thermodynamic equations, DefAP allows the rapid exploration of a material's defect chemistry allowing direct comparison with experimental observations. Rapid exploration is supported through the use of autoplotting with carefully considered automatic data labelling and simplification options enabling production of publication quality plots. DefAP offers a wide range of options for the calculation of defect and carrier concentrations that can be customised by the user to suit the material studied and an extensive suite of options have been designed for the study of extrinsic defects (e.g. dopants or impurities). The capabilities of DefAP are demonstrated in this paper by studying intrinsic defects in YBa2Cu3O7, P doping in Si, Am accumulation in PuO2, and simultaneous build-up of T and He in Li2TiO3.
查看更多>>摘要：In this paper we have investigated the physical and transport properties of Bismuth Selenide, (Bi2Se3) intercalated with Silver (Ag) (Gold (Au) is included for comparison) via dynamical mean field theory with local density approximation. The band structure of Bi2Se3 with a Dirac cone is strongly influenced by the intercalation phenomena at moderate densities which eventually leads to an orbital selective metal insulator transition leading to superconductivity at low temperatures. The claims on the orbital selectivity are substantiated by computing the density of states. While the onset of superconducting correlations at low temperatures are supported by a sudden drop in the resistivity as a function of temperature and the nature of susceptibility. Further the Fermi surface (FS) maps for low and high temperature yields no FS reconstruction.
查看更多>>摘要：Materials strength plays a key role in determining the mechanical response of engineered structures. As such, accurate strength models are crucial in simulations involving complex loading conditions, particularly when deformation in the plastic regime is deemed important. In this work, a Gaussian process based surrogate for a finite element simulation of a Taylor impact test is developed and used for Bayesian calibration of the Preston- Tonks-Wallace strength model. The surrogate model is shown to closely approximate the salient features of the Taylor cylinder deformation and is validated against simulation output before being used in the strength model calibration routine. The results show that Taylor impact test data can be used in the calibration of constitutive equations through the use of a combination of data science techniques, namely Gaussian processes and Bayesian inference.
Peng, JianBridges, Craig A.Lee, SangkeunHaynes, J. Allen...
7页
查看更多>>摘要：Although it is of scientific and practical importance, the state-of-the-art of predicting the thermal expansion of oxides over broad temperature and composition ranges by physics-based atomistic simulations is currently limited to qualitative agreements. We present an emerging machine learning (ML) approach to accurately predict the thermal expansion of cubic oxides with a dataset consisting of experimentally measured lattice parameters while using the metal cation polyhedron and temperature as descriptors. High-fidelity ML models that can accurately predict temperature- and composition-dependent lattice parameters of cubic oxides with isotropic thermal expansions have been successfully trained. The ML-predicted thermal expansions of oxides not included in the training dataset have shown good agreement with available experiments. The limitations of the current approach and challenges to go beyond cubic oxides with isotropic thermal expansion are also briefly discussed.
查看更多>>摘要：MoS2/WS2 heterostructures are widely used in photonic and optoelectronic devices due to their excellent electronic properties and high chemical stability. Herein, we systematically investigated the graphdiyne@MoS2/WS2 heterojunction which demonstrates enhanced performance in the short-wavelength infrared regime. The bidirectional heterostructures have a much smaller bandgap (0.495 eV) compared to MoS2/WS2 (1.71 eV), which will extend the light absorption wavelengths. Further, the perpendicular electric field can effectively tune the band alignment of the bidirectional heterostructures. The critical electric fields, at which the transformation from type-I to type-II and semiconductor-to-metal transition occur, are calculated to be 0.2 V/A and 0.5 V/A, respectively. Our results show that the bidirectional heterostructures graphdiyne@MoS2/WS2 could be applied in the field of infrared photonics and optoelectronics.
查看更多>>摘要：Electronic and magnetic properties of sub-unit cell Fe2O3 (0001) films with variant thicknesses (N = 1 ~ 6, the number of Fe-O octahedral slabs) on the Al2O3 (0001) substrate are investigated by first-principles calculations. Five different magnetic configurations are comparatively studied:(i) Type I (++|- - ) with spins parallel within each Fe-O octahedral slab and antiparallel between two neighboring Fe-O octahedral slabs; (ii) Type II (+- |+- ) with spins antiparallel within each Fe-O octahedral slab and between two neighboring Fe-O octahedral slabs; (iii) Type III (++|++) with spins parallel for all Fe; (iv) Type IV (++|+- ) with spins parallel and antiparallel within each Fe bilayer but parallel between two neighboring Fe-O octahedral slabs; and (v) Type V (- +|+- ) with spins antiparallel within each Fe-O octahedral slab but parallel between two neighboring Fe-O octahedral slabs. It is found that ferromagnetic configuration (++) is stabilized for monolayer (N = 1) Fe2O3 with the lowest formation energy. The magnetic property of sub-unit cell Fe2O3 (0001) films depends on the film thickness. The Fe2O3 thin films comprising of odd number (N = 1, 3, 5) of Fe-O octahedral slabs are ferromagnetic, while those of even number (N = 2, 4, 6) of Fe-O octahedral slabs are antiferromagnetic. The band gap of sub-unit cell Fe2O3 films is obviously lower than that of the bulk. These findings can not only reveal the magnetic coupling nature in subunit cell antiferromagnetic crystals, but also promote the applications of Fe2O3 ultrathin films in magnetic and electronic devices.
查看更多>>摘要：Gas-phase GeMgn- (n = 2-12) clusters were fully researched through CALYPSO and Gaussian software with DFT in this work. Structural evolution studies show that all GeMgn- (n = 3-12) clusters grow based on tetrahedron like and tent-like geometries. It is found that GeMg8- cluster possesses the highest relative stability and can be regarded as a "magic " cluster. The charge transfer property is illustrated by calculations showing that Ge atoms always passively accept electrons, while Mg-n hosts always lose electrons. The valence electron configuration confirms that the cluster formation is mainly originated from the interaction of the 4s4p-orbitals hybridization of Ge with the 3s3p-orbitals hybridization of Mg atoms. The simulated PES of the ground state of GeMgn- (n = 2-12) clusters were also reported. ELF analysis indicates that Mg-Mg covalent bonding occurs in clusters larger than GeMg4- and Ge-Mg bonding is affected by Mg-Mg bonding into the low ELF region. DOS analysis was implemented for the GeMg8- cluster and it can be found that the Ge and Mg atoms contribute to the orbitals mainly from the sigma-bonds. Finally, to provide data support for finding GeMg8- cluster in spectroscopic experiments, theoretical calculations of IR and Raman spectra of GeMg8- were performed.
NSTL
Elsevier