Del Nero, J.Sampaio-Silva, A.Ferreira, D. F.Silva Jr, C. A. B....
6页
查看更多>>摘要：Recently, Me-Graphene (Me-G) was proposed as a graphene (G) allotrope with sp(2)-sp(3) hybridization, near zero Poisson's ratio, sizeable band gap, and high carrier mobility. In this work, we replicate three partially hydro-genated Me-Graphene NanoRibbon (Me-GNR) relaxed unit cells (C13H4, C26H4 and C39H4) of different widths (Me-GNR1, Me-GNR2 and Me-GNR3) and investigate how these molecular devices behave under strain (compression and distension) via DFT/NEGF. Our results show that edge hydrogenation present: (i) metallic behavior for three devices under equilibrium or strain through band structure (BS) and density of states (DOS) at V-e = 0 V which is confirmed by charge density and liquid charge; (ii) negative differential resistance (NDR) for three devices under compression and plateau (resonance) to six other devices; (iii) larger widths increase current and ohmic region; (iv) Molecular Projected Self-Consistent Hamiltonian (MPSH) states that participate of electronic transport are from HOMO -1 up to LUMO + 1; (v) how applied external bias voltage in the device (V-e) affects energy levels distribution through projected density of state (PDOS) and transmittance. These results make Me-GNR be highly promising in nanoelectronics applications such as resonant tunnel diode (RTD) and field effect transistors (FET).
查看更多>>摘要：As an important micro-structure, grain boundary plays a significant role in the micro-structure evolution and mechanical property of metallic materials. In this study, comprehensive molecular dynamics simulations were performed to investigate the propagation mechanisms of intergranular cracks along [1100] symmetric tilt grain boundaries in magnesium bicrystals under tensile loading conditions. The effects of grain boundary misorientation angle, temperature and solid solution were considered. The results show: At low temperature, most of the cracks with different misorientation angles propagate by the brittle cleavage mechanism, which generally agrees with the theoretical predictions based on the Rice's model. With increasing the temperature, the crack propagation mechanism changes, on the one hand, from brittle cleavage to void nucleation, growth and coalescence; on the other hand, the local plastic deformation becomes favorable near the crack tip, due to the dislocation emission and nanograin nucleation via the split of original grain boundary, which relaxes the stress concentration and shields the crack tip. Also, the brittle-to-ductile transition is observed due to the effect of temperature. By adding the alloying elements of Al, Ca, Zn, it is seen that the strength of the grain boundary is enhanced. This work provides insights into the understanding of the ductility of magnesium and its alloys.
查看更多>>摘要：In this paper we continue to develop our structural optimization algorithm built earlier on a numerical platform, the Genetic Hybrid Algorithm (GHA). Our goal now is to extend our algorithm to oxides, find an effective way to search for the known global minimum, alpha-quartz as a test case, and report our results and findings for this system. We studied unit cells of different sizes: 18, 36 and 72 atoms, but most of the presented results are for cases with 18 and 36 atoms. The algorithm makes heavy use of the basin hopping method for searching for the global minimum of the system. We show how we were able to apply basin hopping most effectively in this case and which variables were of importance.We identify three other low energy structures near the global minimum structure, that trap the search. We show that the energy guided basin hopping can be detrimental to the search and structure-based guiding works more reliably. Two different structure based guides were used, one that tries to maximize the shortest silicon-silicon bond in the cell, while the other tries to maximize the calculated order parameter. The guiding was implemented by generating multiple different options for the basin hopping jumps, and doing weighted choosing on those options based on their properties.
查看更多>>摘要：As an insulating material, polyimide (PI) has low intrinsic thermal conductivity and high dielectric constant under high temperature conditions, which causes surface charge accumulation and severely limits the performance of insulation. In this paper, by adapting two-dimensional boron nitride nanosheets (BNNSs), a new type of material model with a PI-BNNS composite structure was established based on a molecular dynamics (MD) simulation method. Meanwhile, the thermal parameter, mechanical parameters, and electrical parameters of models with different doping concentrations at different temperatures were calculated. The results showed that the filling of BNNSs significantly improved the comprehensive performance by changing dielectric constant, breakdown field strength, thermal conductivity and so on. Furthermore, to reveal the microcosmic mechanism of the doping effect, the interfacial interaction intensity was analyzed by calculating the surface binding energy between PI/BNNS. With increasing doping ratio, the van der Waals interaction significantly increased, thus improving the phonon transfer capacity from electron movement to lattice vibration, leading to the mechanical properties and thermal conductivity of the materials significantly improved with increasing doping ratio. The increase in surface binding energy also leads to a deeper trap to capture the charge and produces charge shielding layers to improve the breakdown strength of the system.
查看更多>>摘要：We explore proton diffusion in hydrated, maleic-acid-functionalized chitosan membranes using ab initio molecular dynamics (AIMD) simulations. Our simulations show that more frequent proton hopping between water molecules leads to an increase in the proton diffusion coefficient at higher water content in membranes based on 50 and 100% de-acetylated maleic chitosan. Moreover, mobile protons interact with the oxygen atoms of the 50% de-acetylated polymer's acetyl groups, making them susceptible to protonation. The maleic acid group's three oxygen atoms hydrogen-bond to water molecules in the membrane channels and are protonated less frequently than the acetyl groups.
Rath, SmarakPriyanga, G. SudhaNagappan, N.Thomas, Tiju...
10页
查看更多>>摘要：An approach that would allow quick determination of compositions that are most likely to be direct band gap materials would significantly accelerate research on light-harvesting materials. Inorganic perovskites are attractive for this purpose since they afford compositional flexibility, while also offering stability. Here, ABX(3) inorganic perovskites (A and B are cations and X is an anion) are classified into direct band gap and indirect band gap materials by using the XGBOOST (eXtreme Gradient BOOST) classifier. We use a dataset containing 1528 ABX(3) compounds (X = O, F, Cl, Br, I, S, Se, Te, N, or P) along with information on the nature of their band gap (direct or indirect). All the data is taken from the Materials Project database. Descriptors for these materials are generated using the Matminer python package. Ten-fold cross-validation with the XGBOOST classifier is used on the dataset and the average accuracy is found to be 72.8%. To generate a confusion matrix, the dataset is once again split into a training set and a testing set after cross-validation. Subsequently, the confusion matrix is generated for that particular test set. It is found that the precision for the prediction of direct band gap materials is 81% i.e., 81% of the materials predicted to be direct band gap materials are actually direct band gap materials. Thus, machine learning can be an effective tool for discovering novel direct band gap perovskites. Finally, SHAP (SHapley Additive exPlanations) analysis is performed to determine the most important descriptors. One key insight gained from the SHAP analysis is that the absence of transition metals and elements belonging to groups IIIA to VIIIA with atomic number greater than 20 increases the probability of the perovskite having a direct band gap.
Cooke, Peter I. C.Magdau, Ioan B.Ackland, Graeme J.
13页
查看更多>>摘要：We calculate the eigenstates of a diatomic molecule in a range of model mean-field potentials, and evaluate the evolution of their associated Raman spectra with field strength. We demonstrate that dramatic changes in the appearance of the Raman spectrum for a diatomic molecule occur without any associated change in the symmetry of the surrounding potential. The limiting cases of the quantum eigenstates correspond, in the classical sense, to free rotation, and libration of well-oriented molecules. However, there are also many mixed modes which are neither rotons nor librons. The consequence for Raman spectroscopy is a series of complications - the non-harmonic potential splits the Raman active modes, and breaks the selection rules on forbidden modes. The mass-dependence of the various states is different - rotors, oscillators and reorientations have 1/m, 1/root m and weaker mass dependence respectively. This may allow one to identify the character of the mode with isotope spectroscopy. However it is complicated by mixed modes and transitions between two different eigenstates with different character. We conclude that significant changes in the Raman spectrum of molecular systems are insufficient to demonstrate a phase transition since such changes can also occur in a fixed symmetry potential upon increasing field strength.
查看更多>>摘要：Quaternary Heusler Alloys (QHAs) have become increasingly attractive as thermoelectric and spintronic mate-rials. Density functional theory (DFT) calculations are utilized to investigate the structural, dynamic, elastic, thermodynamic, electronic, magnetic, thermoelectric properties are studied for the new ZrTiRhZ (Z = Ge, Sn) QHAs. Based on the energy minimization, these two new alloys are stable in Type-III structure. The two QHAs are found to be half-metallic with a semiconducting behavior in minority-spin channel and a spin-polarization of 100%. In addition, they show a total magnetic moment of 3 mu B obeying the Slater Pauling rule (Mtot = (Ztot-21) mu B). The semi-classical Boltzmann theory are used to calculate the transport coefficients (Seebeck coefficient (S), electrical conductivity (a), electronic conductivity (kappa e) and power factor (PF), whereas the lattice thermal conductivity (kappa L) is calculated by using the Slack model. The highest values of the figure-of-merit (ZT) are 0.51 and 2.92 for ZrTiRhSn and ZrTiRhGe QHAs, respectively. The half-metallic behavior and high figure-of-merit values of ZrTiRhZ (Z = Ge, Sn) QHAs are promising for applications in spintronic and thermoelectric devices.
查看更多>>摘要：Material properties and fracture characteristics are among the most prominent parameters that should be considered for a wide range of graphene applications. This article reviews recent advances in theoretical studies on the mechanical properties and fracture behaviors of graphene, focusing on the effect of various simulation models. Most studies investigated single-layer graphene sheets (SLGSs) under uniaxial tensile tests using different common interatomic potentials, particularly AIREBO. Although researchers have examined a similar problem, specifically for pristine graphene, the differences in the reported values are considerable. These discrepancies are most evident in fracture strength, failure strain, and Young's modulus. The cause of this issue has not been well explained in former research, and there are still controversies. So far, only a handful of studies have addressed this issue. The out-of-plane effects and defining different shapes for an initial defect/crack are some of the explored factors. This investigation helps to comprehend these points and somewhat clarifies the reasons for the discrepancies in the literature.
查看更多>>摘要：The present work investigated the O-2-adsorption behaviors on the {110} surface of binary MC and ternary M6C6 (M-6 = Zr5Ti, Zr5Ta, Hf5Ti, Hf5Ta) carbides via the first-principles calculations. Several structural units of ternary carbides are first constructed for the calculations, in which the Zr5TiC6 structure with the substitutional Ti atoms in an ordered packing is the most stabilized configuration for O-2-adsorption due to the most negative adsorption energy. The additions of Ti and Ta into ZrC and HfC could result in different distributions of electric structures and more negative primary O-2-adsorption energies in ternary carbides, indicating that Ti and Ta have much stronger interactions with O-2 than the base element Zr or Hf. For the secondary O-2-adsorption, the addition of Ti renders the Zr5TiC6 and Hf5TiC6 carbides with more positive adsorption energies compared with ZrC and HfC, which would prohibit effectively the further oxidation into the matrix, leading to an improvement of oxidation resistance of carbides. However, the total O-2-adsorption energies in Ta-added Zr5TaC6 and Hf5TaC6 carbides are the most negative, indicating that the addition of Ta is not conducive to anti-oxidation.
NSTL
Elsevier