We present the first large-scale molecular dynamics simulations of hexane on graphite that completely reproduces all experimental features of the melting transition. The canonical ensemble simulations required and used the most realistic model of the system: (i) fully atomistic representation of hexane; (ii) explicit site-by-site interaction with carbon atoms in graphite; (iii) CHARMM force field with carefully chosen adjustable parameters of non-bonded interaction; (iv) numerous $\ge$ 100 ns runs, requiring a total computation time of ca. 10 CPU-years. This has allowed us to determine correctly the mechanism of the transition: molecular reorientation within lamellae without perturbation of the overall adsorbed film structure. We observe that the melted phase has a dynamically reorienting domain-type structure whose orientations reflect that of graphite.
Simulation evidence of an incipient triple point is reported for xenon submonolayers adsorbed on the (111) surface of platinum. This is in stark contrast to the "normal" triple point found in simulations and experiments for xenon on the basal plane surface of graphite. The motions of the atoms in the surface plane are treated with standard 2D "NVE" molecular dynamics simulations using modern interactions. The simulation evidence strongly suggests an incipient triple point in the 120-150 K range for adsorption on the Pt (111) surface while the adsorption on graphite shows a normal triple point …
Simulations of the Chain Length Dependence of the Melting Mechanism in Short-Chained n-alkane Monolayers on Graphite
用分子动力学模拟研究了一系列短链正烷烃、正辛烷（n-C8 H 18）、正癸烷（n-C10 H 22）和正十二烷（n-C12 H 26）在石墨基底表面上的固体单分子膜的熔融转变。利用以前的实验观察这些单分子膜的固相行为，本研究调查的温度依赖性的阶段和相变在这三个单分子膜在固-流相变，并比较所观察到的熔化行为，以前的研究己烷和丁烷单分子膜。特别是，这项研究似乎表明，随着链长的增加，在烷基链中形成的笨拙缺陷的熔融转变的依赖性更大。根据先前提出的足迹减少机制和其中从能量上否定了笨拙缺陷的形成的变化，模拟似乎表明癸烷和十二烷单层通常同样依赖于笨拙缺陷的形成以发生熔融转变，而辛烷单层似乎具有较少的依赖性，但遵循在丁烷和己烷单层中熔化的先前研究中建立的趋势。此外，与最近对己烷单层的研究相比，发现从固体人字形相到取向有序中间相的相变表现出一些差异，这可以解释为源于笨拙缺陷的更大影响。比较实验熔化温度提供在可能的情况下，和应用程序涉及薄膜操纵和润滑进行了讨论。
We present a combined experimental and theoretical study of the self-diffusion of ammonia on exfoliated graphite. Using neutron time-of-flight spectroscopy we are able to resolve the ultrafast diffusion process of adsorbed ammonia, NH$_3$, on graphite. Together with van der Waals corrected density functional theory calculations we show that the diffusion of NH$_3$ follows a hopping motion on a weakly corrugated potential energy surface with an activation energy of about 4 meV which is particularly low for this type of diffusive motion. The hopping motion includes further a significant number o…
A few atomic layers of helium adsorbed on graphite have been attracting much attention as one of the ideal quantum systems in two dimension. Although previous reports on neutron diffraction have shown fundamental structural information in these systems, there still remain many open questions. Here, we propose surface crystal truncation rod (CTR) scatterings using synchrotron radiation X-rays as a promising method to reveal surface and interface structures of helium films on graphite at temperatures below 2 K, based on the preliminary experimental results on a monolayer of He-4 on a thin graphi…
The study of the adsorption phenomenon of helium began many decades ago with the discovery of graphite as a homogeneous substrate for investigation of physically adsorbed monolayer films. In particular, helium monoatomic layers on graphite were found to exhibit a very rich phase diagram. In the present work we have investigated the adsorption phenomenon of helium atoms on graphene and silicene substrates by means of density functional theory with Born-Oppenheimer approximation. Helium-substrate and helium-helium interactions were considered from first principles. Vibrational properties of adso…
The sliding motion of gold slabs adsorbed on a graphite substrate is simulated using molecular-dynamics. The central quantity of interest is the mean lateral force, i.e., the kinetic friction rather than the maximum lateral forces, which correlate with the static friction. For most set-ups, we find Stokesian damping to resist sliding. However, velocity-insensitive (Coulomb) friction is observed for finite-width slabs sliding parallel to the armchair direction if the bottommost layer of the three graphite layers is kept at zero stress rather than at zero displacement. Although the resulting kin…
Commensurate-Incommensurate Transition in Submonolayer $^3$He on Graphite
University of Hyogo（兵库大学）；National Institute of Advanced Industrial Science and Technology (AIST)（产业技术综合研究所）；The University of Osaka（大阪大学）；The University of Tokyo（东京大学）
Spurred by the increasing needs in electrochemical energy storage devices, the electrode/electrolyte interface has received a lot of interest in recent years. Molecular dynamics simulations play a proeminent role in this field since they provide a microscopic picture of the mechanisms involved. The current state-of-the-art consists in treating the electrode as a perfect conductor, precluding the possibility to analyze the effect of its metallicity on the interfacial properties. Here we show that the Thomas-Fermi model provides a very convenient framework to account for the screening of the ele…
Great enthusiasm in single atom catalysts (SACs) for the N2 reduction reaction (NRR) has been aroused by the discovery of Metal (M)-Nx as a promising catalytic center. However,the performance of available SACs,including poor activity and selectivity,is far away from the industrial requirement because of the inappropriate adsorption behaviors of the catalytic centers. Through the first principles high throughput screening, we find that the rational construction of Fe-Fe dual atom centered site distributed on graphite carbon nitride (Fe2/gCN) compromises the ability to adsorb N2H and NH2, achiev…
