scholarly journals TO THE PROBLEM OF APPLICABILITY OF THE TAMMAN TEMPERATURE CONCEPT TO NANOSIZED OBJECTS: TO THE 160TH ANNIVERSARY OF GUSTAV TAMMAN

2021 ◽  
pp. 503-512
Author(s):  
Владимир Михайлович Самсонов ◽  
Игорь Владимирович Талызин ◽  
Владимир Владимирович Пуйтов ◽  
Сергей Александрович Васильев
Keyword(s):  
Molecular Dynamics ◽  
Surface Layer ◽  
Melting Point ◽  
Au Nanoparticles ◽  
Small Object ◽  
Temperature Elevation ◽  
The Core ◽  
Local Species ◽  
Temperature Concept ◽  
Quasicrystalline Structure

Во введении представлен краткий критический обзор имеющихся интерпретаций температуры Таммана, обычно определяемой как T = 0,5T, и температуры Хюттига T = 0,3T, где T - макроскопическое значение температуры плавления материала. Для наночастиц предложено в указанных выше определяющих соотношениях заменить T на температуру плавления малого объекта T, т.е. определить T как 0,5T, а T как 0,3T. В молекулярно-динамических экспериментах на наночастицах Au, осуществленных с помощью LAMMPS, было установлено, что при температуре T=T как в центральной части ГЦК-наночастицы, так и в её поверхностном слое возникают локальные очаги квазикристаллической структуры, которые попеременно идентифицируются программой OVITO то как имеющие кристаллическую структуру, то как не имеющие кристаллической упорядоченности. Однако, вопреки мнению Э. Рукенштейна (1984), при T=T жидкий слой на поверхности кристаллической наночастицы еще не образуется. Вместе с тем в наших молекулярно-динамических экспериментах не обнаружено какое-либо проявление температуры Хюттига T в структуре кристаллических наночастиц Au. The introduction provides a brief critical review of the available definitions and interpretations of the Tamman temperature, usually defined as T = 0,5T, and of the Hüttig temperature T = 0,3T where T is the macroscopic value of the melting point of the material. For a nanoparticle we propose to replace in the above relations T by the melting temperature of the small object T , i.e. to define T as 0,5T and T as 0,3T . In our molecular dynamics experiments on Au nanoparticles, carried out using the LAMMPS program, we found that at the temperature T = T , in both the central part of the fcc nanoparticle (the core) and in its surface layer (the shell), some local species of a quasicrystalline structure appear which are alternately identified either as crystalline or as non-crystalline by the OVITO program. However, contrary to opinion of E. Rukenstein (1984), at T = T , a liquid layer on the surface of the crystalline nanoparticle is not formed yet. However, a liquid-like layer was gradually developed in the course of the further temperature elevation. At the same time, in our molecular dynamics experiments we did not reveal any manifestation of the Huttig temperature T in the structure of crystalline Au nanoparticles reproduced in our molecular dynamics experiments. It is also of interest that in our molecular dynamics experiments the nanoparticle sintering took place not only above the Tammann temperature but below it as well.

Development and Application of Chen-Mobius Lattice Inversion Potential for Pd-Au Alloy

2011 ◽  
Vol 1369 ◽  
Author(s):  
Xianbao Duan ◽  
Zhengzheng Chen ◽  
Neeti Kapur ◽  
Xianghong Hao ◽  
Kyeongjae Cho ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Particle Size ◽  
Melting Point ◽  
Size Dependence ◽  
Au Nanoparticles ◽  
Inversion Method ◽  
Potential Applications ◽  
Simulation Results ◽  
Dynamics Simulations ◽  
Binary Nanoparticles

ABSTRACTBimetallic Pd-Au nanoparticles have received much attention due to their potential applications in catalysis. We have developed a Pd-Au alloy potential based on Chen-Mobius lattice inversion method and applied it to the investigation of the melting of Pd-Au binary nanoparticles via molecular dynamics simulations. Our simulation results show the particle size dependence of the melting point and an enrichment of Au atoms to the surface near melting temperature.

Molecular Dynamics Study of Thermodynamic Properties of Cu-Pd Clusters

2015 ◽  
Vol 723 ◽  
pp. 747-751
Author(s):  
H. Huang ◽  
Z.F. Cheng ◽  
X.Y. Xiao ◽  
J.H. Xia ◽  
T.Z. Liu ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Melting Point ◽  
Core Layer ◽  
Dynamics Simulation ◽  
Bimetallic Clusters ◽  
Embedded Atom Method ◽  
Fourth Layer ◽  
The Core ◽  
Embedded Atom ◽  
Pd Clusters

This paper studies the melting of Cu-Pd bimetallic clusters with different Pd positions by using molecular dynamics simulation with a general embedded-atom method. The melting of clusters with 55 Pd atomic distributing different positions where the core-layer, second-layer, third-layer, fourth-layer and mixed. It is found that the changing of melting point is strongly related to the position of Pd atomic. The results indicate that the Pd atoms doped in the core layer and surface layer, below the melting point of the second layer and third layer. Meanwhile, this indicate that the Pd atomic doped in the second layer and third layer, the structure of cluster is relatively stable. The irregular phenomena of the melting were induced by the Pd position. This gives a new method to tune the melting point in bimetallic clusters.

Molecular Dynamics Simulations on Melting of Aluminum

2013 ◽  
Vol 423-426 ◽  
pp. 935-938 ◽  
Author(s):  
Ji Feng Li ◽  
Xiao Ping Zhao ◽  
Jian Liu
Keyword(s):  
Molecular Dynamics ◽  
Melting Point ◽  
Molecular Dynamics Simulations ◽  
High Pressures ◽  
Ambient Pressure ◽  
Initial Porosity ◽  
Equilibrium Melting Point ◽  
Porosity Effect ◽  
Dynamics Simulations ◽  
Experimental Melting Point

Molecular dynamics simulations were performed to calculate the melting points of perfect crystalline aluminum to high pressures. Under ambientpressure, there exhibits about 20% superheating before melting compared to the experimental melting point. Under high pressures, thecalculated melting temperature increases with the pressure but at a decreasing rate, which agrees well with the Simon's melting equation. Porosity effect was also studied for aluminum crystals with various initial porosity at ambient pressure, which shows that the equilibrium melting point decreases with the initial porosity as experiments expect.

On the interface of organic aerosols: molecular level understanding of surface melting, mixing and water adsorption/desorption dynamics

2021 ◽  
Author(s):  
Josip Lovrić ◽  
Xiangrui Kong ◽  
Sofia M. Johansson ◽  
Erik S. Thomson ◽  
Jan B. C. Pettersson
Keyword(s):  
Physical Chemistry ◽  
Molecular Dynamics ◽  
Melting Point ◽  
Molecular Beam ◽  
Molecular Level ◽  
Organic Aerosols ◽  
Md Simulations ◽  
Valeric Acid ◽  
Good Representative ◽  
Hydrophilic Character

<p>The detailed description of organic aerosols surfaces in the atmosphere remains an open issue, which limits our ability to understand and predict environmental change. Important research questions concern the hydrophobic/hydrophilic character of fresh and aged aerosols and the related influence on water uptake in solid, liquid as well in intermediate state.  Also, surface characterization remains big challenge but we find it reachable by conjunction of Molecular Dynamics (MD) simulations and the environmental molecular beam (EMB) experimental method.  A  picture of the detailed molecular-level behavior of water molecules on organic surfaces is beginning to rise based on detailed experimental and theoretical studies; one example is a recent study that investigates water interactions with solid and liquid n-butanol near the melting point [1], another example focus on interaction of water with solid nopinone [2]. From the other side, in order to characterize surface properties during and before melting we employ MD simulations of n-butanol, nopinone and valeric acid. Nopinone (C<sub>9</sub>H<sub>14</sub>O) is a reaction product formed during oxidation of β-pinene and has been found in both the gas and particle phases of atmospheric aerosol. n-butanol (C<sub>4</sub>H<sub>9</sub>OH) is primary alcohol, naturally occurs scarcely and here serves as good representative for alcohols. In the same way valeric acid (CH<sub>3</sub>(CH<sub>2</sub>)<sub>3</sub>COOH) serves as a good representative for a family of carboxylic acids. Valeric acid is, as n-butanol, straight-chain molecule. We show that a classical force field for organic material is able to model crystal and liquid structures. The surface properties near the melting point of the condensed phase are reported, and the hydrophobic and hydrophilic character of the surface layer is discussed.  Overall surface melting dynamic is presented and quantified in the terms of structural and geometrical properties. Mixing of a methanol with the solid nopinone surface is examined and hereby presented.</p><p><strong>References</strong></p><p>[1] Johansson, S. M., Lovrić, J., Kong, X., Thomson, E. S., Papagiannakopoulos, P., Briquez, S., Toubin, C, Pettersson, J. B. C. (2019). Understanding water interactions with organic surfaces: environmental molecular beam and molecular dynamics studies of the water–butanol system. Physical Chemistry Chemical Physics. https://doi.org/10.1039/C8CP04151B   </p><p>[2] Johansson, S. M., Lovrić, J., Kong, X., Thomson, E. S., Hallquist, M., & Pettersson, J. B. C. (2020). Experimental and Computational Study of Molecular Water Interactions with Condensed Nopinone Surfaces Under Atmospherically Relevant Conditions. The Journal of Physical Chemistry A, acs.jpca.9b10970. https://doi.org/10.1021/acs.jpca.9b10970</p><p>Keywords: Molecular Dynamics, organic crystal, organic aerosols, water uptake, surface procesess, molecular level</p>

Surface and Near-Surface Atom Dynamics During Low Energy Xe Ion Bombardment of Si and Fcc Surfaces

1990 ◽  
Vol 193 ◽  
Author(s):  
M. V. R. Murty ◽  
H. S. Lee ◽  
Harry A. Atwater
Keyword(s):  
Molecular Dynamics ◽  
Surface Layer ◽  
Ion Bombardment ◽  
Low Energy ◽  
Surface Processes ◽  
Defect Production ◽  
Near Surface ◽  
Qualitative Nature ◽  
Dynamics Simulations ◽  
Atom Dynamics

ABSTRACTSurface and near-surface processes have been studied during low energy Xe ion bombardment of Si (001) and fcc surfaces using molecular dynamics simulations. Defect production is enhanced near the surface of smooth Si (001) surfaces with respect to the bulk in the energy range 20–150 eV, but is not confined exclusively to the surface layer. The extent and qualitative nature of bombardment-induced dissociation of small fcc islands on an otherwise smooth fcc (001) surface is found to depend strongly on island cohesive energy.

scholarly journals How Atoms of Polycrystalline Nb 20.6 Mo 21.7 Ta 15.6 W 21.1 V 21.0 refractory High-Entropy Alloys Rearrange during the Melting Process

2021 ◽  
Author(s):  
Shin-Pon Ju ◽  
Chen-Chun Li
Keyword(s):  
Molecular Dynamics ◽  
Melting Point ◽  
Single Crystal ◽  
Melting Temperature ◽  
Md Simulation ◽  
Melting Process ◽  
Structural Rearrangement ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Melting Mechanism

Abstract The melting mechanism of single crystal and polycrystalline Nb 20.6 Mo 21.7 Ta 15.6 W 21.1 V 21.0 RHEAs was investigated by the molecular dynamics (MD) simulation using the 2NN MEAM potential. For the single crystal RHEA, the density profile displays an abrupt drop from 11.25 to 11.00 g/cm 3 at temperatures from 2910 to 2940 K, indicating all atoms begin significant local structural rearrangement. For polycrystalline RHEAs, a two-stage melting process is found. In the first melting stage, the melting of the grain boundary (GB) regions firstly occurs at the pre-melting temperature, which is relatively lower than the corresponding system-melting point. At the pre-melting temperature, most GB atoms have enough kinetic energies to leave their equilibrium positions, and then gradually induce the rearrangement of grain atoms close to GB. In the second melting stage at the melting point, most grain atoms have enough kinetic energies to rearrange, resulting in the chemical short-ranged order (CSRO) changes of all pairs.

scholarly journals Phonon Abundance-Stiffness-Lifetime Transition from the Mode of Heavy Water to Its Confinement and Hydration

2018 ◽  
Author(s):  
Chang Sun
Keyword(s):  
Molecular Dynamics ◽  
Heavy Water ◽  
Surface Stress ◽  
Vibration Mode ◽  
Hydration Shell ◽  
Solution Viscosity ◽  
The Core ◽  
Spatially Resolved ◽  
Skin Formation ◽  
Phonon Lifetime

<div>A combination of the temporally- and spatially-resolved phonon spectroscopy has enabled calibration of hydrogen bond transition from the vibration mode of heavy water to the core-shelled nanodroplet and the sub-nanosized ionic hydration shell in terms of phonon abundance-lifetime-stiffness. It is uncovered that charge injection by salt solvation and skin formation by molecular undercoordination (often called confinement) share the same supersolidity of H–O (D–O as a probe) bond contraction, O:H elongation, and electron polarization. The bond transition stems the solution viscosity, surface stress, and slows down the molecular dynamics. The skin reflection further hinders phonon energy dissipation and thus lengthens the phonon lifetime of the nanodroplet.</div>

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