Comparative study of nudged elastic band and molecular dynamics methods for diffusion kinetics in solid-state electrolytes

Considerable efforts are being made to transition current lithium-ion and sodium-ion batteries towards the use of solid-state electrolytes.Computational methods,specifically nudged elastic band(NEB)and molecular dynamics(MD)methods,provide powerful tools for the design of solid-state electrolytes.The MD method is usually the choice for studying the materials involving complex multiple diffusion paths or having disordered structures.However,it relies on simulations at temperatures much higher than working temperature.This paper studies the reliability of the MD method using the system of Na diffusion in MgO as a benchmark.We carefully study the convergence behavior of the MD method and demonstrate that total effective simulation time of 12 ns can converge the calculated diffusion barrier to about 0.01 eV.The calculated diffusion barrier is 0.31 eV from both methods.The diffusion coefficients at room temperature are 4.3×10^(-9) cm^(2)⋅s^(−1) and 2.2×10^(-9) cm^(2)⋅s^(−1),respectively,from the NEB and MD methods.Our results justify the reliability of the MD method,even though high temperature simulations have to be employed to overcome the limitation on simulation time.

Structural,electronic and elastic properties of YCu from first principles

The structural, electronic and elastic properties of YCu compound in the B2 （CsCl） phase were investigated using the density functional theory （DFT） within the generalized gradient approximation （GGA）. The electronic density of states （DOS） obtained in this way accorded weU with the results of a recent study utilizing the full-potential linearized augmented plane wave （FLAPW） method. We also found that the density of d-states at the Fermi energy was low. The calculated equilibrium properties such as lattice constant, bulk modulus and its first derivative, and the elastic constants were in good agreement with experimental and theoretical results.

Band structure properties of elastic waves propagating in the nanoscaled nearly periodic layered phononic crystals

The localization factor is used to describe the band structures for P wave propagating normally in the nanoscaled nearly periodic layered phononic crystals. The localization factor is calculated by the transfer matrix method based on the nonlocal elastic continuum theory.Three kinds of nearly periodic arrangements are concerned, i.e., random disorder, quasiperiodicity and defects. The influences of randomly disordered degree of the sub-layer＇s thickness and mass density, the arrangement of quasi-periodicity and the location of defect on the band structures and cut-off frequency are analyzed in detail.

Effects of RE(La,Ce)on fcc-bcc martensitic transformation of iron via Bain transformation path

The fundamental understanding of the effects of rare earth(RE)on the phase transformation of Fe-based alloys is essential in the development of advanced RE-containing high strength steels.In this work,we investigated the effects of La and Ce on the martensitic phase transformation of Fe in terms of the driving force and minimum energy path(MEP)using the first-principles calculations.The calculations of formation energy show that the RE substitution increases the stabilization of fcc-Fe and decreases that of bcc-Fe,thus decreasing the driving force of phase transformation.Meanwhile,the analysis based on the generalized solid-state nudged elastic band(G-SSNEB)method indicates that in the RE-containing systems,an additional energy barrier appears when the phase transformation proceeds along the Bain transition path to c/a ratio of 1.14 in the FM state,which is associated with a sudden decrease in magnetization due to the hybridization between the orbits of the RE atoms and those of the nearest neighbor Fe atoms.The results of potential-energy surfaces(PES)confirm that magnetic ordering and lattice volume change simultaneously with the Bain transition,and in comparison to pure Fe,the variation between the onset and the end structural volumes of the phase transformation is slight for the REcontaining Fe systems.

Stability, Accuracy and Cost of NEB and String Methods

In this paper,the zero-temperature string method and the nudged elastic band method for computing the transition paths and transition rates between metastable states are investigated.The stability,accuracy as well as computational cost of the two methods are discussed.The results are verified by numerical experiments.