Maksimenko, V. N.Lipnitskii, A. G.Kartamyshev, A., IPoletaev, D. O....
9页
查看更多>>摘要：Tungsten, as the most refractory metal, is applied in fusion reactor in parts subjected to high temperatures and strong neutron irradiation. These factors lead to intense diffusion processes causing degradation of the material. Experimental investigations under such conditions are usually highly complicated and cannot provide a comprehensive understanding of the occurring phenomena. Therefore, their combination with theoretical approaches is required. One of the most robust approaches to simulate diffusion processes is molecular dynamics simulations based on classical interatomic potentials. It allows modeling relatively large samples consisting of several grains, grain boundaries, dislocations, and other types of defects for a reasonable computational time. The reliable simulations of the diffusion process require interatomic potentials satisfying the following criteria: prediction of melting point and thermal expansion as close as possible to the experimental values because the diffusion coefficient strongly depends on the homologous temperature and size factor. In the present paper, we present the new interatomic potential for tungsten, developed within the N-body approach, which reproduces the experimental value of melting temperature (3695 K) and thermal expansion at temperatures up to a melting point. The calculated diffusion coefficient demonstrates adequate agreement with experimental results. The constructed potential is applicable for simulation of processes involving diffusion, one of which is the irradiation damage.
查看更多>>摘要：More and more attention has been paid to the role of the desolvation effect of ions in the electrolyte for supercapacitor in improving its capacitance. We have previously calculated that the complete desolvation size of Li+, Na+, and K+ in the basal plane pore (BPP) is 4.7 angstrom, 4.4 angstrom, and 4.4 angstrom, but the desolvation of the edge plane pore (EPP) is not considered. So in this work, the complete desolvation behaviour of Li+, Na+, and K+ at the EPP in the pore structure of porous carbon materials in the aqueous solution is studied by first-principles calculations. The calculation results show that the solvated Li+ can be completely desolvated when the pore size of EPP is less than 3.61 angstrom, while the solvated Na+ and K+ will not be desolvated under any pore size of EPP. Combining the work of this paper with our previous work, solvated Li+ has desolvation behaviour in both EPP and basal plane pore (BPP). Four models of pores are constructed by the combination of EPP and BPP to discuss the storage of desolvated Li+ in porous carbon materials. The calculation results show that the necking flask like EPP-BPP pore with - 3.61 angstrom outer pore and - 7.4 angstrom inner pore can accommodate more Li+ improving the capacitance of the supercapacitors. The desolvation mechanism of EPP and BPP on the solvated ions has important theoretical guiding significance for designing the pore structure of porous carbon materials.
Papageorgiou, D. G.Andrea, M.Kordos, K.Lidorikis, E....
11页
查看更多>>摘要：Non-fullerene acceptors (NFAs) have demonstrated remarkable performance when used in bulk heterojunction organic solar cell devices. Their exceptional properties, such as the ability to tune their electronic properties by chemical modifications, increased absorption in the visible and near infrared part of the spectrum, and general ease of synthesis, make them a key alternative for traditional fullerene-based acceptors. IDIC is a typical NFA material having a five-membered fused ring core and strong electron withdrawing end groups. In this work we use a multiscale computational approach based on a hopping model and Marcus' charge transport theory to investigate electron and hole transport in crystal and amorphous IDIC samples. The basic transport parameters, namely reorganization energy, electronic couplings and site energies are calculated and compared with the corresponding values for fullerene-based acceptors where available in the literature. Electrostatic and induction contributions to the total energetic disorder are also examined and discussed. Using Kinetic Monte Carlo simulation, the electric field and temperature dependence of mobility is systematically evaluated for electrons and holes, and the data are fitted against the widely used Gaussian Disorder Model. We find that compared to the commonly used PCBM fullerene acceptor, IDIC has larger reorganization energy and similar energetic disorder. However, it exhibits comparable electron mobility, due to enhanced electronic couplings with neighboring molecules in the crystalline brickwork-like structure.
查看更多>>摘要：Variations in the chemical composition or thermomechanical processing of metallic materials result in a vast landscape of possible microstructural morphologies. While this creates ample opportunities for alloys with improved mechanical performance, the design process is challenging due to the morphological complexity and the range of deformation micro-mechanisms involved. Empirically based statistical approaches are well suited to address some of these challenges. Previously, a model based on n-point statistics and principal component analysis was successfully used for predicting damage nucleation based on the microstructural morphology of dual-phase steels. Here, we give an in-depth exploration and analysis of such algorithms as applied to experimental data. First, we investigate model architecture by implementing and testing over 1000 model variants. This leads to improved predictive ability and several alternate architectures including one with a Fourier transformation instead of a n-point statistics transformation. Second, we analyze the noise, resolution and data quantity impact to give guidelines on the necessary data required to train a predictive model. Third, we investigate which morphological features are utilized by the model to make predictions by inputting artificiallyconstructed microstructures, inverting the model, examination of the basis image, and variation of model hyperparameters. It is found that grain boundary fluctuations less than 1 mu m are correlated to damage nucleation. This is consistent with observations in the literature on the effect of grain size and interconnected martensite regions on damage nucleation. Furthermore, it may give insights into the superior mechanical properties of alloys with bimodal grain size distributions. This demonstrates a unique approach of elucidating morphological effects from a single alloy by exploiting microstructural heterogeneity. It may be applied to other microstructures as well.
查看更多>>摘要：Nanoparticles (NPs) are widely used to tune the mechanical and physical properties of carbon nanotube (CNT) networks in many practical applications. However, the distribution of NPs in CNT networks and their effects on microstructural evolutions and mechanical properties remain elusive. We employed the coarse-grained molecular dynamics (CGMD) simulations to systematically investigate these issues. First, we found that compared to ambient temperature and the frequency of cyclic loads, the relative cohesion energy of NPs and strain amplitude of cyclic loads are more important factors for controlling the aggregation of NPs; it was also revealed that NPs with larger relative cohesion energy and in larger-strain cyclic loads would aggregate more severely in CNT networks. Second, we observed that the Young's modulus and the tensile strength of the material can be increased by up to -3.2 and -2.0 times, respectively, at the critical volume fraction of NPs (-21.6%). Finally, the underlying mechanisms by which NPs strengthen the inter-tube joints and constrain the bundling of CNTs are unveiled. These results should be useful for the optimal design of CNT-based advanced materials.
Qureshi, Muhammad WaqasMa, XinxinTang, GuangzePaudel, Ramesh...
19页
查看更多>>摘要：Using first-principles density functional theory (DFT), the ground state physical properties of the newly synthesized noble-metal-containing Ti3AuC2 MAX phase have been investigated. The effect of transition-element Ti replacement (V and Cr) on physical properties, including structural, elastic, electronic, thermal, and optical are presented. The optimized lattice parameters of Ti3AuC2 MAX phase are in good agreement with the experimental values and decrease when we replace Ti with V and then Cr. The magnetic properties of M3AuC2 are predicted by using generalized gradient approximation (GGA) incorporating onsite electron correlation parameter (Hubbard U parameter) within DFT. Out of three studied MAX phases, V3AuC2 and Cr3AuC2 phases exhibit magnetism. The thermodynamical stability of M3AuC2 (M = Ti, V, and Cr) phases is discussed by the formation enthalpy with respect to their most competing phases. The electronic structure reveals that these phases have metallic nature and are electrically anisotropic. The M-element replacement has an effect on the bonding properties of M3AuC2. The bonding between M-C is in the order of Cr3AuC2 > V3AuC2 > Ti3AuC2 according to their peak positions and heights of density of states in the occupied site, which is also confirmed from the charge density distribution. The elastic properties indicate that M3AuC2 phases are ductile, machinable, less stiff, and better resistant to thermal shock and are elastically anisotropic. To understand the properties of M3AuC2 for the extreme environment, we employed a quasi-harmonic Debye model at the pressure and temperature range of 0-50 GPa and 0-1600 K, respectively. Additionally, we evaluated thermal conductivity and melting temperature to further understand the potential of these MAX phases in coating applications at elevated temperature. In relation to optical properties, these MAX phases have a reasonable absorption coefficient in the visible as well as in the ultra-violet regions. The reflectivity of M3AuC2 phases is polarization dependent and of 45 % against the visible region, which reveals its potential as coating material to minimize solar heating.
查看更多>>摘要：We propose here a method to generate random networked amorphous structure using only readily available short-range properties like bond lengths, bond angles and connectivity of the constituents. This method is a variant of Monte-Carlo (MC) method wherein the basic constituents of an amorphous network i.e. rigid polyhedral units are connected randomly obeying certain steric constraints. The algorithm is designed to reproduce the medium-range order universally observed in glasses. The method resembles the reverse MC (RMC) method where a random move of an atom inside a box is accepted or rejected depending upon whether it decreases or increases the deviation from the experimentally observed features. However unlike RMC, this method does not demand large experimental sets of scattering data which are difficult to obtain for glasses. It rather relies on the stochasticity of MC method to produce glassy structures. The method presented here examines the possibility of developing glassy structures without employing either the computationally demanding melt-quench simulation or the information demanding RMC method. The algorithm is first validated against SiO2 glass structure by comparing with the available structures from other methods and experimental data. The method is then extended for developing more complex Iron Phosphate Glass (IPG) structures and a comparative study of the generated models is done with existing models of IPG developed using melt-quench scheme in classical Molecular Dynamics (MD). Through this study we conclude that the IPG model developed using MC method and subsequently equilibrated using MD agrees in all structural aspects with the model of IPG generated using melt-quench simulation, projecting the current recipe as an interesting alternative to melt-quench simulation for developing glass models.
查看更多>>摘要：In this paper, the segregation tendency of elements M (Re, Co, Cr, Mo, Ti) near the complex and intrinsic stacking fault (CSF and SISF) on gamma'- Ni3Al (111) plane as well as the influence of the segregation on the mechanical properties were studied by the first-principle method. The results show that Co and Cr atoms tend to segregate to CSF and Co also has segregation tendency for SISF. Comparison of metallic radius of alloying element can predict preliminary the segregation tendency which decreases along with the increase of metallic radius of M, except for Re. Segregation of M depends on their strong interactions with their surrounding Ni atoms near SFs, rather than the minimization of elastic strain. In addition, the Re effect is not induced by its interaction with the two SFs in gamma' phase. Meanwhile, the effects of segregated elements Co and Cr on the mechanical properties are further dis-cussed. The results show that segregation of the two elements to CSF results in higher interfacial stability and the improvement of plastic deformation ability, but Co near SISF is beneficial to increase work-hardening. This work will provide insight for the composition design and improvement of processing technology of Ni-based super-alloys and even other alloys.
查看更多>>摘要：Classical molecular dynamics is one of the most important methods for exploring material properties and uncovering physical mechanism, but the predicted results strongly depend on the used potentials. Using ab initio molecular dynamics simulations to obtain atomic conformations and the associated energy and force as training set and testing set, we developed a Gaussian approximation potential model for single-layer MoS2 based on the machine learning method. The phonon dispersion relations calculated from the developed potential are compared well to that of density functional theory, which confirms the accuracy of the developed potential in the harmonic interaction. We also calculated the temperature-dependent Raman-active phonon frequency and linewidth of the single-layer MoS2 using classical molecular dynamics. The obtained temperature-dependent phonon frequency and linewidth are compared with the corresponding experimental results, indicating that the developed potential still has high accuracy in the anharmonic interactions. The detailed process and methods to obtain the MoS2 potential in this work can be extended and applied to the development and investigation of the high-precision potential of emerging new materials.
查看更多>>摘要：In this study, a group of W-Ta-V ternary alloys with continuously changing compositions was investigated using the first principles approach. The structures and elastic properties of the ternary W-Ta-V alloys were investigated. The alloys had the random BCC structure. The elastic constants, elastic moduli, and other mechanical parameters of the ternary W-Ta-V alloys were determined. The results showed that the elastic properties of the ternary W-TaV alloys generally decrease with the addition of Ta and V. At the same time, the ductility of W was effectively improved by alloying Ta and V. The electronic structure analysis, including density of state and electron localization function, showed that alloying Ta and V improves the metallicity of W, and the types and strength of bonds affect the stability and elastic modulus of the alloys.
NSTL
Elsevier