Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
- Discipline
- Keyword
-
- Molecular dynamics simulation (3)
- Density functional calculation (2)
- Photoelectron spectroscopy (2)
- 2D high-density ice (1)
- 2D low-density ice (1)
-
- 2D monolayer ice clathrate (1)
- Ab initio molecular dynamics (1)
- Amorphous-to-amorphous transition. (1)
- Anion photoelectron spectroscopy (1)
- Antiicing (1)
- Articles (1)
- Atomic energy distribution (1)
- Bandgap engineering (1)
- Bilayer hexagonal silicon (1)
- Bilayer methane hydrate (1)
- Bilayer water and ice (1)
- Boron-nitride nanoribbons (1)
- Carbon nanotube (1)
- Carrier mobility (1)
- Chemical modification (1)
- Cluster (1)
- Clusters (1)
- Copper (1)
- Density functional calculations (1)
- Direct bandgap (1)
- Dual-scale hierarchical structure (1)
- Electronic structures (1)
- First-principles calculations (1)
- Free-energy barrier (1)
- Global minimum search. (1)
Articles 151 - 167 of 167
Full-Text Articles in Physical Sciences and Mathematics
Imaging Point Defects In A Liquid Environment: A Model Afm Study, Kenichiro Koga, Xiao Cheng Zeng
Imaging Point Defects In A Liquid Environment: A Model Afm Study, Kenichiro Koga, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
Effects of the liquid on atomic force microscopy (AFM) imaging are examined for a model system consisting of a hexagonal flake of seven Lennard-Jones (LJ) atoms as a multiatom tip, a monolayer of LJ crystal containing a single point defect as a substrate, and three-site model water as the liquid. A previous simulation [Koutsos et al., Europhys. Lett. 26, 103 (1994)] has shown that the true atomic resolution of a point defect cannot be achieved in vacuum by use of the multiatom tip. Here we examine the feasibility of such atomic resolution when both the tip and substrate are immersed …
A Patching Model For Surface Tension And The Tolman Length, T.V. Bykov, Xiao Cheng Zeng
A Patching Model For Surface Tension And The Tolman Length, T.V. Bykov, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
In the framework of density functional theory (DFT), a patching model for the density profile of the liquid–vapor interface is developed. The patching is based on analytical expressions of the asymptote of the density profiles. Derived from the model the surface tension of planar liquid–vapor interface as well as the Tolman length can be computed from analytic expressions. Two prototype systems are considered; the Yukawa and the Lennard-Jones. As a result, the temperature dependence of the surface tension as well as the Tolman length are obtained. The results are compared with numerical DFT calculations.
Hydrogen Bonding And Cooperative Effects In Mixed Dimers And Trimers Of Methanol And Trifluoromethanol: An Ab Initio Study, Ruben D. Parra, Xiao Cheng Zeng
Hydrogen Bonding And Cooperative Effects In Mixed Dimers And Trimers Of Methanol And Trifluoromethanol: An Ab Initio Study, Ruben D. Parra, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
Ab initio calculations are used to provide information on the mixed dimers and cyclic trimers of the methanol-trifluoromethanol system. In order to better understand the systems, the monomers and their corresponding dimers and trimers are also investigated. Molecular structures and harmonic frequencies are obtained at the B3LYP/6-311++G(d,p) level. Interaction energies are calculated with the MP2 and B3LYP methods using the 6-311++G(d,p), 6-311++G(2d,2p), and 6-311++G(3d,2p) basis sets for the dimers and heterodimers. The 6-311++G(d,p) basis set was used to calculate the …
Molecular Dynamics Study Of A Phase-Separating Fluid Mixture Under Shear Flow, Ryoichi Yamamoto, Xiao Cheng Zeng
Molecular Dynamics Study Of A Phase-Separating Fluid Mixture Under Shear Flow, Ryoichi Yamamoto, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
Molecular dynamics simulation is carried out to study domain structures and rheological properties of a two-dimensional phase-separating binary fluid mixture under shear flow. In the early stage of the phase separation, anisotropic composition fluctuations appear immediately after the quench. As the domain grows, the anisotropy in the composition fluctuations increases. The quenched system eventually reaches a dynamical steady state, in which anisotropic domain structures are preserved. In the steady state, the shortest characteristic length scale R⊥ of domains decreases with increasing shear rate γ̇ as R⊥∼γ̇-1/3. Stringlike domain structures are observed in the strong shear regime, …
Formation Free Energy Of Clusters In Vapor-Liquid Nucleation: A Monte Carlo Simulation Study, K.J. Oh, Xiao Cheng Zeng
Formation Free Energy Of Clusters In Vapor-Liquid Nucleation: A Monte Carlo Simulation Study, K.J. Oh, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
The formation free energy of clusters in a supersaturated vapor is obtained by a constrained Monte Carlo technique. A key feature of this approach is to set an upper limit to the size of cluster. This maximum cluster size serves essentially as an extra thermodynamic variable that constrains the system. As a result, clusters larger than the critical cluster of nucleation in the supersaturated vapor can no longer grow beyond the limiting size. Like changing the overall density of the system, changing the maximum cluster size also results in a different supersaturation and thereby a different formation free energy. However, …
Thermodynamic Expansion Of Nucleation Free-Energy Barrier And Size Of Critical Nucleus Near The Vapor-Liquid Coexistence, Kenichiro Koga, Xiao Cheng Zeng
Thermodynamic Expansion Of Nucleation Free-Energy Barrier And Size Of Critical Nucleus Near The Vapor-Liquid Coexistence, Kenichiro Koga, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
Nucleation free-energy barrier height and size of the critical nucleus are expanded in powers of the chemical potential difference between the supersaturated vapor (or expanded liquid) in the metastable state and the saturated vapor-liquid system in the stable equilibrium state at the same temperature. The coefficients in the expansions are expressed in terms of the thermodynamic properties at the stable equilibrium state. Comparisons with the results obtained from the density-functional calculation for nucleation of the Lennard–Jones fluid show that systematic improvement in predicting properties of the critical nucleus, either liquid droplet or vapor cavity, is achieved by adding the higher …
Effect Of Uniform Electric Field On Homogeneous Vapor–Liquid Nucleation And Phase Equilibria. Ii. Extended Simple Point Charge Model Water, G.T. Gao, K.J. Oh, Xiao Cheng Zeng
Effect Of Uniform Electric Field On Homogeneous Vapor–Liquid Nucleation And Phase Equilibria. Ii. Extended Simple Point Charge Model Water, G.T. Gao, K.J. Oh, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
The effects of a uniform electric field on homogeneous vapor–liquid nucleation of the extended simple point charge (SPC/E) model water have been simulated. A grand canonical Monte Carlo simulation approach [I. Kusaka et al., J. Chem. Phys. 108, 3416 (1998)], which directly gives the equilibrium distribution of physical clusters, is employed to calculate the formation free energy of the SPC/E water cluster. The results show that the formation free energy is lowered in a uniform field if the chemical potential of the supersaturated vapor is fixed; in this case, the field enhances the rate of nucleation. However, if the vapor …
The Effect Of A Uniform Electric Field On Homogeneous Vapor–Liquid Nucleation In A Dipolar Fluid. I. Stockmayer Fluid, K.J. Oh, G.T. Gao, Xiao Cheng Zeng
The Effect Of A Uniform Electric Field On Homogeneous Vapor–Liquid Nucleation In A Dipolar Fluid. I. Stockmayer Fluid, K.J. Oh, G.T. Gao, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
The rate of homogeneous vapor–liquid nucleation is controlled mainly by the Gibbs formation free energy of critical clusters. Within the framework of thei/υ cluster theory of Reiss and co-workers, the formation free energies of Stockmayer clusters in the presence of a uniform electric field are determined. The Helmholtz free energy of the clusters, an input required in the i/υ cluster theory, is calculated via Monte Carlo simulations. The most significant result is that as a uniform electric field is applied the formation free energy at fixed supersaturation of the vapor becomes larger than that in the absence …
Validity Of Tolman’S Equation: How Large Should A Droplet Be?, Kenichiro Koga, Xiao Cheng Zeng, A.K. Shchekin
Validity Of Tolman’S Equation: How Large Should A Droplet Be?, Kenichiro Koga, Xiao Cheng Zeng, A.K. Shchekin
Xiao Cheng Zeng Publications
Surface tension and the length δ (distance between the Gibbs surface of tension Rs and the equimolar surface Re) of simple liquid droplet (Lennard-Jones and Yukawa) are computed over a wide range of droplet sizes up to about 4x106 molecules. The study is based on the Gibbs theory of capillarity combined with the density–functional approach to gas–liquid nucleation. Since this method provides behavior of the surface tension fully consistent with the tension of the planner surface, the constant in Tolman’s equation δx can be determined unequivocally from the asymptotic behavior of σ s . Comparison …
Contribution Of The Center-Of-Mass Fluctuation Of A Liquid Cluster To The Free Energy: A Monte Carlo Simulation Study, K.J. Oh, Xiao Cheng Zeng
Contribution Of The Center-Of-Mass Fluctuation Of A Liquid Cluster To The Free Energy: A Monte Carlo Simulation Study, K.J. Oh, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
The contribution of the center-of-mass (CM) fluctuation of a liquid cluster to the Helmholtz free energy was first discussed by Reiss, Katz, and Cohen (RKC). They argued that this contribution can be assessed via the free energy difference between the cluster with a fixed boundary centered on a fixed CM, and the cluster in which the CM was allowed to fluctuate. They estimated the free energy difference is to be about 20 kbT. Here kb is the Boltzmann constant and T is the temperature of the system. To examine this estimate, Abraham et al. later calculated …
Freezing Of Confined Water: A Bilayer Ice Phase In Hydrophobic Nanopores, Kenichiro Koga, Xiao Cheng Zeng, Hideki Tanaka
Freezing Of Confined Water: A Bilayer Ice Phase In Hydrophobic Nanopores, Kenichiro Koga, Xiao Cheng Zeng, Hideki Tanaka
Xiao Cheng Zeng Publications
Molecular dynamics simulations were performed to study the phase behavior of a thin film of water confined to a slit nanopore with smooth walls. A first-order water-to-ice freezing transition has been observed. The resulting ice, which is a crystal of bilayer consisting of rows of distorted hexagons, does not resemble any ice crystals found so far. The confined water contracts upon freezing when the confinement load is low ( ∼0.5 kbar) and expands when the load is high (10 kbar). The residual entropy of the bilayer ice can be calculated exactly, which is about half of the entropy of the …
Scanning Motions Of An Atomic Force Microscope Tip In Water, Kenichiro Koga, Xiao Cheng Zeng
Scanning Motions Of An Atomic Force Microscope Tip In Water, Kenichiro Koga, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
Integral equation techniques are used to study scanning motions of a single-atom tip of the atomic force microscope (AFM) over a rigid, hydrophobic monolayer substrate in water. The calculated force curve is found to be oscillatory, in agreement with recent AFM experiments, which can lead to multiple scanning trajectories for the tip under a constant load. The unique trajectory along which the system is thermodynamically stable is revealed. This study shows that the tip may take a hopping motion over a defect-free substrate due to layering of water molecules between the tip and substrate.
Toward A Molecular Theory Of Vapor-Phase Nucleation. V. Self-Consistency In The Decoupled Dimer Limit, K.J. Oh, Xiao Cheng Zeng, H. Reiss
Toward A Molecular Theory Of Vapor-Phase Nucleation. V. Self-Consistency In The Decoupled Dimer Limit, K.J. Oh, Xiao Cheng Zeng, H. Reiss
Xiao Cheng Zeng Publications
The previous papers of this series introduced a molecular i / υ cluster theory of vapor phase nucleation. This theory differs from most conventional ones in that the cluster (due to fluctuation) is not only characterized by its number of particles i but also by a spherical volume υ. Thus the free energy of formation of the cluster is not merely a one-dimensional function of the number of particles i but a two-dimensional function of both i and v (i.e., it is a free energy surface). In the first stage of this development (Refs. 1–3) the theory is based on …
Solvent-Induced Interactions Between Hydrophobic And Hydrophilic Polyatomic Sheets In Water And Hypothetical Nonpolar Water, Kenichiro Koga, Xiao Cheng Zeng, Hideki Tanaka
Solvent-Induced Interactions Between Hydrophobic And Hydrophilic Polyatomic Sheets In Water And Hypothetical Nonpolar Water, Kenichiro Koga, Xiao Cheng Zeng, Hideki Tanaka
Xiao Cheng Zeng Publications
Hydrophobic and hydrophilic interactions are two major intermolecular forces between hydrophobic nonpolar and hydrophilic polar sites of macromolecules or materials surfaces in solvents. To further understand these two interactions at the microscopic level, an idealized polyatomic model is devised, which includes hydrophobic, hydrophilic, and partially hydrophilic polyatomic planar square molecular sheets. The hydrophobic molecular sheet is composed of the Lennard-Jones particles while the hydrophilic molecular sheet consists of positive and negative charge sites. In the framework of the extended reference interaction site model integral equation theory the solvent-induced interactions (or the potential of mean forces) between two parallel molecular sheets …
Vapor–Liquid Coexistence Of Quasi-Two-Dimensional Stockmayer Fluids, G.T. Gao, Xiao Cheng Zeng, Wenchuan Wang
Vapor–Liquid Coexistence Of Quasi-Two-Dimensional Stockmayer Fluids, G.T. Gao, Xiao Cheng Zeng, Wenchuan Wang
Xiao Cheng Zeng Publications
A quasi-two-dimensional (2D) Stockmayer model is developed in which the center of mass of the molecule is confined on a plane while the dipole of the molecule can rotate freely in three dimensional space. This model entails essential characteristics of systems such as dipolar molecules physisorbed on a solid surface, or a Langmuir monolayer consisting of short-chain molecules with a dipolar tail. The Gibbs ensemble Monte Carlo technique is employed to determine the vapor– liquid equilibria of the model fluids. An Ewald sum for this quasi-2D model is formulated to account for the long-range dipolar interactions. Three systems with different …
Thermal Nucleation And Cavitation In Helium-3 Fluids, Xiao Cheng Zeng, D.W. Oxtoby, E. Cheng
Thermal Nucleation And Cavitation In Helium-3 Fluids, Xiao Cheng Zeng, D.W. Oxtoby, E. Cheng
Xiao Cheng Zeng Publications
We have investigated droplet nucleation and bubble cavitation in the quantum fluid helium-3 based on a nonlocal density-functional approach. A marked effect of droplet (or bubble) curvature on the rate of droplet nucleation or cavitation has been found. Without considering this curvature effect (as in the classical theory of nucleation) the droplet nucleation rate for helium-3 could be underestimated (i.e., near 1 K) or overestimated (i.e., near 2.5 K) by orders of magnitude, respectively; for bubble cavitation, the rate could be underestimated by more than twenty orders of magnitude (near 1 K).
Gas–Liquid Nucleation In Two-Dimensional Fluids, Xiao Cheng Zeng
Gas–Liquid Nucleation In Two-Dimensional Fluids, Xiao Cheng Zeng
Xiao Cheng Zeng Publications
A nonclassical theory of nucleation, based on the density-functional (DF) approach, is developed for the gas–liquid transitions of two-dimensional (2D) Lennard-Jones (LJ) fluids. The methods of Weeks–Chandler–Andersen perturbation theory are used to approximate the LJ potential with a temperature-dependent hard-disk diameter plus an attractive tail. The resulting free energy functional is then used to calculate the free energy barrier to nucleation. We find that the curvature of the 2D nucleus is not important to the rate of nucleation (in contrast to the 3D counterpart). The effect of curvature is readily inferred from the ratio of nucleation rate from classical Becker–Dö̈ring …