RESUMEN
We employ Monte Carlo simulation in the semi-grand canonical ensemble to obtain the coarse-grained free energy corresponding to an embedded-atom method description of a binary alloy. In particular, the Ginzburg-Landau free energy for a Cu-Ni alloy was determined from a tabulated histogram of the joint probability density of composition, energy, and volume. Using histogram reweighting techniques, the free energy is extrapolated to a range of points in parameter space from a small number of simulations. The results are interpreted by comparing the free energy with that corresponding to a regular solution model of an alloy. In addition, we obtain expressions for thermodynamic quantities in terms of the joint cumulants of the probability density at a given temperature and chemical potential difference. These expressions may then be likewise extrapolated to obtain the dependence of the composition on the temperature and the chemical potential difference over a wide range of parameter space.
RESUMEN
The adhesion and friction between pairs of ordered and disordered self-assembled monolayers on SiO2 are studied using molecular dynamics. The disorder is introduced by randomly removing chains from a well ordered crystalline substrate and by attaching chains to an amorphous substrate. The adhesion force between monolayers at a given separation increases monotonically with chain length at full coverage and with coverage for fixed chain length. Friction simulations are performed at shear velocities between 0.02-2 m/s at constant applied pressures between 200 and 600 MPa. Stick-slip motion is observed at full coverage but disappears with disorder. With random defects, the friction becomes insensitive to chain length, defect density, and substrate.
RESUMEN
Molecular dynamics simulations for three embedded atom method (EAM) function sets are used to determine the liquid/vapor surface tension gamma for Al, Ni, Cu, Ag, and Au. The three EAM models differ in both the functional forms employed and the fitting procedure used. All the EAM potentials underestimate gamma but one of the models performs consistently better than the others. We show that including a correction to the local charge density associated with gradients in the density together with exploiting the invariance of the EAM potentials to appropriate transformations in the charge density can lead to improved values for gamma, as well as for solid free surface energies, within existing EAM function sets.
