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Register a new userReconciling simulated melting and ground-state properties of metals with a modified embedded-atom method potential
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We propose a modification of the embedded-atom method-type potential aiming at reconciling simulated melting and ground-state properties of metals by means of classical molecular dynamics. Considering titanium, magnesium, gold, and platinum as case studies, we demonstrate that simulations performed with the modified force field yield quantitatively correctly both the melting temperature of the metals and their ground-state properties. It is shown that the accounting for the long-range interatomic interactions noticeably affect the melting point assessment. The introduced modification weakens the interaction at interatomic distances exceeding the equilibrium one by a characteristic vibration amplitude defined by the Lindemann criterion, thus allowing for the correct simulation of melting, while keeping its behavior in the vicinity of the ground state minimum. The modification of the many-body potential has a general nature and can be applicable to metals with different characteristics of the electron structure as well as for many different molecular and solid state systems experiencing phase transitions.
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We develop an Fe-C-H interatomic potential based on the modified embedded-atom method (MEAM) formalism based on density functional theory to enable large-scale modular dynamics simulations of carbon steel and hydrogen.
Transition metal dichalcogenides (TMDs) are layered semiconducting van der Waal crystals and promising materials for a wide range of electronic and optoelectronic devices. Realizing practical electrical and optoelectronic device applications requires a connection between a metal junction and a TMD semiconductor. Hence, a complete understanding of electronic band alignments and the potential barrier heights governing the transport through a metal-TMD-metal junction is critical. But, there is a knowledge gap; it is not clear how the energy bands of a TMD align while in contact with a metal as a function of the number of layers. In pursuit of removing this knowledge gap, we have performed conductive atomic force microscopy (CAFM) of few layered (1-5) MoS2 immobilized on ultra-flat conducting Au surfaces (root mean square (RMS) surface roughness <0.2 nm) and indium tin oxide (ITO) substrate (RMS surface roughness <0.7 nm) forming a vertical metal (conductive-AFM tip)-semiconductor-metal device. We have observed that the current increases as the number of layers increases up to 5 layers. By applying Fowler-Nordheim tunneling theory, we have determined the barrier heights for different layers and observed that the barrier height decreases as the number of layers increases. Using density functional theory (DFT) calculation, we successfully demonstrated that the barrier height decreases as the layer number increases. By illuminating the TMDs on a transparent ultra-flat conducting ITO substrate, we observed a reduction in current when compared to the current measured in the dark, hence demonstrating negative photoconductivity. Our study provides a fundamental understanding of the local electronic and optoelectronic behaviors of TMD-metal junction, and may pave an avenue toward developing nanoscale electronic devices with tailored layer-dependent transport properties.
In this paper, we investigate the ground-state properties of a bosonic Tonks-Girardeau gas confined in a one-dimensional periodic potential. The single-particle reduced density matrix is computed numerically for systems up to $N=265$ bosons. Scaling analysis of the occupation number of the lowest orbital shows that there are no Bose-Einstein Condensation(BEC) for the periodically trapped TG gas in both commensurate and incommensurate cases. We find that, in the commensurate case, the scaling exponents of the occupation number of the lowest orbital, the amplitude of the lowest orbital and the zero-momentum peak height with the particle numbers are 0, -0.5 and 1, respectively, while in the incommensurate case, they are 0.5, -0.5 and 1.5, respectively. These exponents are related to each other in a universal relation.
We developed new modified embedded-atom method (MEAM) interatomic potentials for the Mg-Al alloy system using a first-principles method based on density functional theory (DFT). The materials parameters, such as the cohesive energy, equilibrium atomic volume, and bulk modulus, were used to determine the MEAM parameters. Face-centered cubic, hexagonal close packed, and cubic rock salt structures were used as the reference structures for Al, Mg, and MgAl, respectively. The applicability of the new MEAM potentials to atomistic simulations for investigating Mg-Al alloys was demonstrated by performing simulations on Mg and Al atoms in a variety of geometries. The new MEAM potentials were used to calculate the adsorption energies of Al and Mg atoms on Al (111) and Mg (0001) surfaces. The formation energies and geometries of various point defects, such as vacancies, interstitial defects and substitutional defects, were also calculated. We found that the new MEAM potentials give a better overall agreement with DFT calculations and experiments when compared against the previously published MEAM potentials.
The ground state electronic structure and magnetic behaviors of curium dioxide (CmO$_{2}$) are controversial. In general, the formal valence of Cm ions in CmO$_{2}$ should be tetravalent. It implies a $5f^{6.0}$ electronic configuration and a non-magnetic ground state. However, it is in sharp contrast with the large magnetic moment measured by painstaking experiments. In order to clarify this contradiction, we tried to study the ground state electronic structure of CmO$_{2}$ by means of a combination of density functional theory and dynamical mean-field theory. We find that CmO$_{2}$ is a wide-gap charge transfer insulator with strong 5$f$ valence state fluctuation. It belongs to a mixed-valence compound indeed. The predominant electronic configurations for Cm ions are $5f^{6.0}$ and $5f^{7.0}$. The resulting magnetic moment agrees quite well with the experimental value. Therefore, the magnetic puzzle in CmO$_{2}$ can be appropriately explained by the mixed-valence scenario.
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