41 research outputs found
Molecular Dynamics Simulation for the (Magic Number) Size Effect in Nucleation and Evaporation of Clusters
Cluster formation of Lennard-Jones particles (65, 536 atoms in a unit cell with overall number density equal to 0.0149) was simulated by molecular dynamics. The temperature was controlled to decrease linearly with time by various thermostats, starting from a gas state temperature and ending at zero temperature. Nucleation (aggregation) and evaporation processes of clusters are separately analyzed. No particular size dependence in the former process was found. Evaporation process made the clusters into the stable structure of the particular sizes (13, 19, 23, etc.) in cooperate with cooling the clusters
Molecular Dynamics Calculation for the Clustering Process from Gas and Liquid
Molecular dynamics calculation of two clustering processes for atoms of Lennard-Jones (L-J) potential and water molecules is described. One clustering process is under the adiabatic condition from the gas state by lowering of the temperature. Another is thermal decomposition of liquid droplet. The system consists of 8192 L-J atoms or 512 water molecules. Vibrational, rotational, and translational temperature and potential energy were used to analyze the clustering process. Clear magic number was not observed in any proces
Molecular Dynamics Simulation for the Formation of Magic-Number Clusters with a Lennard-Jones Potential
Colossal reversible barocaloric effects in a plastic crystal mediated by lattice vibrations and ion diffusion
Solid-state methods for cooling and heating promise a more sustainable
alternative to current compression cycles of greenhouse gases and inefficient
fuel-burning heaters. Barocaloric effects (BCE) driven by hydrostatic pressure
() are especially encouraging in terms of large adiabatic temperature
changes ( K) and colossal isothermal entropy changes
( JKkg). However, BCE typically require
large pressure shifts due to irreversibility issues, and sizeable
and seldom are realized in a same material. Here, we demonstrate
the existence of colossal and reversible BCE in LiCBH, a
well-known solid electrolyte, near its order-disorder phase transition at
K. Specifically, for GPa we
measured JKkg and K, which individually rival with state-of-the-art
barocaloric shifts obtained under similar pressure conditions. Furthermore,
over a wide temperature range, pressure shifts of the order of GPa yield
huge reversible barocaloric strengths of
JKkgMPa. Molecular dynamics simulations were carried out
to quantify the role of lattice vibrations, molecular reorientations and ion
diffusion on the disclosed colossal BCE. Interestingly, lattice vibrations were
found to contribute the most to while the diffusion of lithium
ions, despite adding up only slightly to the accompanying entropy change, was
crucial in enabling the molecular order-disorder phase transition. Our work
expands the knowledge on plastic crystals and should motivate the investigation
of BCE in a variety of solid electrolytes displaying ion diffusion and
concomitant molecular orientational disorder.Comment: 13 pages, 7 figure
Mixed alkali-ion transport and storage in atomic-disordered honeycomb layered NaKNi2TeO6
Honeycomb layered oxides constitute an emerging class of materials that show interesting physicochemical and electrochemical properties. However, the development of these materials is still limited. Here, we report the combined use of alkali atoms (Na and K) to produce a mixed-alkali honeycomb layered oxide material, namely, NaKNi2TeO6. Via transmission electron microscopy measurements, we reveal the local atomic structural disorders characterised by aperiodic stacking and incoherency in the alternating arrangement of Na and K atoms. We also investigate the possibility of mixed electrochemical transport and storage of Na+ and K+ ions in NaKNi2TeO6. In particular, we report an average discharge cell voltage of about 4 V and a specific capacity of around 80 mAh g–1 at low specific currents (i.e., < 10 mA g–1) when a NaKNi2TeO6-based positive electrode is combined with a room-temperature NaK liquid alloy negative electrode using an ionic liquid-based electrolyte solution. These results represent a step towards the use of tailored cathode active materials for “dendrite-free” electrochemical energy storage systems exploiting room-temperature liquid alkali metal alloy materials
Ring Mechanism of Fast Na+Ion Transport in Na2LiFeTeO6: Insight from MolecularDynamics Simulation
Honeycomb layered oxides have attracted recent attention because of their rich crystal chemistry. However, the atomistic mechanisms of cationic transport in these structures remain vastly unexplored. Herein, we perform an extensive, systematic molecular dynamics study on Na2LiFeTeO6 using combined force-field and first-principles-based molecular dynamics simulations. We use are fined set of inter-atomic potential parameters of a previously reported potential model that represents various structural and transport properties of this recently reported promising material for all-solid-state battery applications. The present simulation study elucidates the roles of octahedral ordering and entropic contributions in Na+-ion distribution in the ab-plane. Our theoretical simulation also develops a ring-like atomistic diffusion mechanism and relevant atomistic energy barriers that help to understand the origin of fast ion conduction in honeycomb layered oxides