The effects of plateau width and step-edge kinking on carbon monoxide (CO)-induced restructuring of platinum surfaces were explored using molecular dynamics (MD) simulations. Platinum crystals displaying four different vicinal surfaces [(321), (765), (112), and (557)] were constructed and exposed to partial coverages of carbon monoxide. Platinum–CO interactions were fit to recent experimental data and density functional theory (DFT) calculations, providing a classical interaction model that captures the atop binding preference on Pt. The differences in Pt–Pt binding strength between edge atoms on the various facets were found to play a significant role in step-edge wandering and reconstruction events. Because the mechanism for step doubling relies on a stochastic meeting of two wandering edges, the widths of the plateaus on the original surfaces were also found to play a role in these reconstructions. On the Pt(321) surfaces, the CO adsorbate was found to assist in reordering the kinked step edges into straight {100} edge segments.

We present a new reverse nonequilibrium molecular dynamics method that can be used with nonperiodic simulation cells. This method applies thermal and/or angular momentum fluxes between two arbitrary regions of the simulation and is capable of creating stable temperature and angular velocity gradients while conserving total energy and angular momentum. One particularly useful application is the exchange of kinetic energy between two concentric spherical regions, which can be used to generate thermal transport between nanoparticles and the solvent that surrounds them. The rotational couple to the solvent (a measure of interfacial friction) is also available via this method. As tests of the new method, we have computed the thermal conductivities of gold nanoparticles and water clusters, the interfacial thermal conductivity (G) of a solvated gold nanoparticle, and the interfacial friction of a variety of solvated gold nanostructures.

4-Cyano-4′-pentylbiphenyl (5CB) is a liquid crystal forming compound with a terminal nitrile group aligned with the long axis of the molecule. Simulations of condensed-phase 5CB were carried out both with and without applied electric fields to provide an understanding of the Stark shift of the terminal nitrile group. A field-induced isotropic–nematic phase transition was observed in the simulations, and the effects of this transition on the distribution of nitrile frequencies were computed. Classical bond displacement correlation functions exhibit a ∼2.3 cm–1 red-shift of a portion of the main nitrile peak, and this shift was observed only when the fields were large enough to induce orientational ordering of the bulk phase. Distributions of frequencies obtained via cluster-based fits to quantum mechanical energies of nitrile bond deformations exhibit a similar ∼2.7 cm–1 red-shift. Joint spatial-angular distribution functions indicate that phase-induced anticaging of the nitrile bond is contributing to the change in the nitrile spectrum.

The mechanism and dynamics of surface reconstructions of Pt(557) and Au(557) exposed to various coverages of carbon monoxide (CO) were investigated using molecular dynamics simulations. Metal–CO interactions were parametrized from experimental data and plane-wave density functional theory (DFT) calculations. The large difference in binding strengths of the Pt–CO and Au–CO interactions was found to play a significant role in step-edge stability and adatom diffusion constants. Various mechanisms for CO-mediated step wandering and step doubling were investigated on the Pt(557) surface. We find that the energetics of CO adsorbed to the surface can explain the step-doubling reconstruction observed on Pt(557) and the lack of such a reconstruction on the Au(557) surface. However, more complicated reconstructions into triangular clusters that have been seen in recent experiments were not observed in these simulations.

We report on simulations of heat conduction through Au(111)/hexane interfaces in which the surface has been protected by a mixture of short- and long-chain alkanethiolate ligands. Reverse nonequilibrium molecular dynamics (RNEMD) was used to create a thermal flux between the metal and solvent, and thermal conductance was computed using the resulting thermal profiles near the interface. We find a nonmonotonic dependence of the interfacial thermal conductance on the fraction of long chains present at the interface and correlate this behavior to both solvent ordering and the rate of solvent escape from the thiolate layer immediately in contact with the metal surface. Our results suggest that a mixed vibrational transfer/convection model is necessary to explain the features of heat transfer at this interface. The alignment of the solvent chains with the ordered ligand allows rapid transfer of energy to the trapped solvent and is the dominant feature for ordered ligand layers. Diffusion of the vibrationally excited solvent into the bulk also plays a significant role when the ligands are less tightly packed.

We have developed a new isobaric−isothermal (NPT) algorithm which applies an external pressure to the facets comprising the convex hull surrounding the system. A Langevin thermostat is also applied to the facets to mimic contact with an external heat bath. This new method, the “Langevin Hull”, can handle heterogeneous mixtures of materials with different compressibilities. These systems are problematic for traditional affine transform methods. The Langevin Hull does not suffer from the edge effects of boundary potential methods and allows realistic treatment of both external pressure and thermal conductivity due to the presence of an implicit solvent. We apply this method to several different systems, including bare metal nanoparticles and nanoparticles in an explicit solvent as well as clusters of liquid water. The predicted mechanical properties of these systems are in good agreement with experimental data and previous simulation work.

With the non-isotropic velocity scaling (NIVS) approach to reverse non-equilibrium molecular dynamics (RNEMD), it is possible to impose an unphysical thermal flux between different regions of inhomogeneous systems such as solid/liquid interfaces. We have applied NIVS to compute the interfacial thermal conductance at a metal/organic solvent interface that has been chemically capped by butanethiol molecules. Our calculations suggest that coupling between the metal and liquid phases is enhanced by the capping agents, leading to a greatly enhanced conductivity at the interface. Specifically, the chemical bond between the metal and the capping agent introduces a vibrational overlap that is not present without the capping agent, and the overlap between the vibrational spectra (metal to cap, cap to solvent) provides a mechanism for rapid thermal transport across the interface. Our calculations also suggest that this is a nonmonotonic function of the fractional coverage of the surface, as moderate coverages allow diffusive heat transport of solvent molecules that have been in close contact with the capping agent.