The solid-liquid interfacial free energy of close-packed metals: hard spheres and the Turnbull coefficient

Largely due to its role in nucleation and crystal-growth, the free energy of the crystal-melt interfacial free energy is an object of considerable interest across a number of scientific disciplines, especially in the materials-, colloid- and atmospheric sciences. Over fifty years ago, Turnbull observed that the interfacial free energies (scaled by the mean interfacial area per particle) of a variety of metallic elements exhibit a linear correlation with the enthalpy of fusion. This correlation provides an important empirical "rule-of-thumb" for estimating interfacial free energies, but lacks a compelling physical explanation. In this work we show that the interfacial free energies for close-packed metals are linearly correlated with the melting temperature, and are therefore primarily entropic in origin. We also show that the slope of this linear relationship can be determined with quantitative accuracy using a hard-sphere model, and that the correlation with the enthalpy of fusion reported by Turnbull follows as a consequence of the fact that the entropy of fusion for close-packed metals is relatively constant.Comment: 3 pages, 1 figure, to appear in J. Chem. Phy

Direct calculation of the crystal-melt interfacial free energies for continuous potentials: Application to the Lennard-Jones system

Extending to continuous potentials a cleaving wall molecular-dynamics simulation method recently developed for the hard-sphere system [Phys.Rev.Lett 85, 4751 (2000)], we calculate the crystal-melt interfacial free energies, $\gamma$, for a Lennard-Jones system as functions of both crystal orientation and temperature. At the triple point, T* = 0.617, the results are consistent with an earlier cleaving potential calculation by Broughton and Gilmer [J. Chem. Phys. {\bf 84}, 5759 (1986)], however, the greater precision of the current calculation allows us to accurately determine the anisotropy of $\gamma$. From our data we find that, at all temperatures studied, $\gamma_{111} < \gamma_{110} < \gamma_{100}$. Comparison is made to the results from our previous hard-sphere calculation and to recent results for Ni by Asta, Hoyt and Karma [Phys. Rev. B, 66 100101(R) (2002)].Comment: 7 pages, 3 figures, 2 table

Molecular dynamics simulation of binary hard-sphere crystal/melt interfaces

We examine, using molecular dynamics simulation, the structure and thermodynamics of the (100) and (111) disordered face-centered cubic (FCC) crystal/melt interfaces for a binary hard-sphere system. This study is an extension of our previous work, [Phys. Rev. E 54, R5905 (1996)], in which preliminary data for the (100) interface were reported. Density and diffusion profiles on both fine- and course-grained scales are calculated and analyzed leading to the conclusion that equilibrium interfacial segregation is minimal in this system.Comment: 7 pages, 7 figures, to appear in Molecular Physic

Solid-liquid interfacial premelting

We report the observation of a premelting transition at chemically sharp solid-liquid interfaces using molecular-dynamics simulations. The transition is observed in the solid-Al/liquid-Pb system and involves the formation of a liquid interfacial film of Al with a width that grows logarithmically as the bulk melting temperature is approached from below, consistent with current theories of premelting. The premelting behavior leads to a sharp change in the temperature dependence of the diffusion coefficient in the interfacial region, and could have important consequences for phenomena such as particle coalescence and shape equilibration, which are governed by interfacial kinetic processes.Comment: 6 pages, 4 figure

Weighted‐density‐functional theory calculation of elastic constants for face‐centered‐cubic and body‐centered‐cubic hard‐sphere crystals

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/97/4/10.1063/1.463059.The isothermal elastic constants for the face‐centered‐cubic (fcc) and body‐centered‐cubic (bcc) hard‐sphere crystal are calculated for a range of densities using the modified weighted‐density functional of Denton and Ashcroft [Phys. Rev. A 3 9, 4701 (1989)]. The fcc elastic constants are shown to be in excellent agreement with the computer simulation data and to represent a significant improvement over the predictions of other density‐functional methods. The bcc crystal is predicted correctly to be unstable to shear, in agreement with simulation. This fact supports the conclusion that the bcc hard‐sphere solid, even though mechanically unstable, is well described by such methods

A molecular-dynamics algorithm for mixed hard-core/continuous potentials

We present a new molecular-dynamics algorithm for integrating the equations of motion for a system of particles interacting with mixed continuous/impulsive forces. This method, which we call Impulsive Verlet, is constructed using operator splitting techniques similar to those that have been used successfully to generate a variety molecular-dynamics integrators. In numerical experiments, the Impulsive Verlet method is shown to be superior to previous methods with respect to stability and energy conservation in long simulations.Comment: 18 pages, 6 postscript figures, uses rotate.st

To Trust or Not: The Effects of Monitoring Intensity on Discretionary Effort, Honesty, and Problem Solving Ability

Managerial accounting researchers and practitioners are increasingly concerned with the effects of formal organizational controls on agent behavior. This three-paper dissertation extends this line of research by experimentally examining the effects of monitoring intensity on three important work behaviors which, generally, are not directly observable by the organizational control system: discretionary effort, problem solving ability, and honesty. Together, these studies help fill a gap in the managerial accounting literature by examining the relationship between the monitoring environment and agent behavior. The principal-agent theory of the firm suggests that tighter monitoring by the principal will increase the agent’s work effort at best, and have no effect at worst. However, the psychology literature suggests that monitoring may actually reduce effort by “crowding out” an individual’s intrinsic motivation to perform unmeasured or unrewarded work related tasks. In Paper 1, I test for the crowding out effect of monitoring and find mixed results. In Paper 2, I investigate the effects of monitoring intensity on various aspects of problem solving ability and creativity. Past research suggests that strict environmental controls can have detrimental effects on creative thinking. I extend this line of literature by investigating how monitoring affects an individual’s problem solving ability. In general, I find that monitoring intensity is negatively associated with problem solving ability. In Paper 3, I investigate how monitoring intensity affects an individual’s propensity toward dishonesty using a 3x2 experimental design where the participants are given a simple task, with a monetary reward based on performance, in one of the three monitoring treatments—trust, human monitoring, or electronic monitoring—and in one of two outcome reporting regimes—self-report or verified. I find an inverted-U shape relationship between monitoring intensity and dishonesty, where dishonesty is highest under human monitoring. Organizations are increasing their use of all types of surveillance and controls, and, in general, trust is increasingly discouraged within organizations. These papers add to the managerial accounting literature by shedding light on how different monitoring environments can change human behavior. This line of research can only increase in importance as regulation increases and monitoring technology becomes more advanced, reliable, and accessible

Generating Generalized Distributions from Dynamical Simulation

We present a general molecular-dynamics simulation scheme, based on the Nose' thermostat, for sampling according to arbitrary phase space distributions. We formulate numerical methods based on both Nose'-Hoover and Nose'-Poincare' thermostats for two specific classes of distributions; namely, those that are functions of the system Hamiltonian and those for which position and momentum are statistically independent. As an example, we propose a generalized variable temperature distribution that designed to accelerate sampling in molecular systems.Comment: 10 pages, 3 figure