Classical Nonequilibrium Molecular Dynamics Research Articles

Molecular Dynamics Evaluation of Thermal Transport in Naked and Oxide-Coated Silicon Nanowires

The thermal conductivities (κ) of Si nanowires (SiNWs) with naked and sub-nm-oxidized surfaces have been evaluated by nonequilibrium classical molecular dynamics simulations. For the naked SiNWs, the dependence of κ on the cross-sectional area qualitatively agreed with previous Monte Carlo simulations and experiments. It was confirmed that κ was not sensitive to cross-sectional shape or crystalline orientation. The κ of the SiOx-coated SiNWs was decreased compared with that of the naked SiNWs when both types of NW had the same crosssection. However, the κ corresponding to the core part of Si (including the interfacial layer between the Si core and surface SiOx) was equivalent to the κ of the naked SiNWs. The presence of a surface oxide does not modulate the internal thermal conduction of the SiNWs.

Ultrafast Energy Transfer from the Intramolecular Bending Vibration to Librations in Liquid Water

A theoretical study of the water bend-to-libration energy transfer in liquid H(2)O has been performed by means of nonequilibrium classical molecular dynamics computer simulations. Attention has been focused on the time scale and mechanism of the decay of the fundamental H(2)O bend vibration and the related issue of the decay of water librational (hindered rotational) excitations, including the important role of that for the excited molecule itself. The time scales found are 270 fs for the decay of the average energy of an H(2)O molecule excited to the nu = 1 state of the bending oscillator and less than 100 fs for excess rotational (librational) kinetic energy, both consistent with recent ultrafast infrared experimental results. The energy flow to the excited molecule rotation and through the first several solvent shells around the excited water molecule is discussed in some detail.

Nonequilibrium molecular dynamics simulations of vibrational energy relaxation of HOD in D2O

Vibrational energy relaxation of HOD in deuterated water is investigated performing classical nonequilibrium molecular dynamics simulations. A flexible SPC/E model is employed to describe the intermolecular interactions and the intramolecular potential of the D(2)O solvent. A more accurate intramolecular potential is used for HOD. Our results for the OH stretch, OD stretch, and HOD bend vibrational relaxation times are 2.7, 0.9, and 0.57 ps, respectively. Exciting the OH stretching mode the main relaxation pathway involves a transition to the bending vibration. These results are in agreement with recent semiclassical Landau-Teller calculations. Contrary to this previous work, however, we observe a strong coupling of bending and OH stretching mode to the HOD rotation. As a result almost half of the total vibrational energy is transferred through the HOD rotation to the bath. At the same time the most efficient acceptor mode is the D(2)O rotation indicating the importance of resonant libration-to-libration energy transfer. We also find significant vibrational excitation of the D(2)O bending mode of the D(2)O solvent by V-V energy transfer from the HOD bending mode.

Classical Simulation of Quantum Energy Flow in Biomolecules

Based on a comparison of classical and quantum-mechanical perturbation theory, the validity of classical nonequilibrium molecular dynamics simulations to describe vibrational energy redistribution in biomolecules is studied. Adopting a small model peptide in aqueous solution as an example, the theory correctly predicts quantum correction factors that need to be applied to the results of classical simulations in order to match the correct quantum results.

Molecular Dynamics Simulation of Interfacial Thermal Resistance Between a (10,10) Carbon Nanotube and SiO2

AbstractUnderstanding thermal transport between carbon nanotubes (CNTs) and dielectric substrates is important both for nanoscale thermal management and CNT device applications. We investi-gate thermal transport between a (10,10) CNT and an SiO2 substrate through non-equilibrium classical molecular dynamics (MD) simulations. The thermal boundary conductance (TBC) is computed by setting up a temperature pulse in the CNT and monitoring its relaxation. The TBC is found to scale nearly linearly with temperature between 200�600 K, where a quantum correction is applied to the CNT heat capacity through its phonon density of states. However, the TBC ap-pears most sensitive to the strength the CNT-substrate interaction, which linearly modulates it between 0.05�0.30 WK-1m-1, in the range suggested by recent experimental data.

Lattice thermal conductivity of SiC nanowires

We present non-equilibrium classical molecular dynamics simulationsfor the lattice thermal transport of SiC nanowires and bulkβ-SiC. The thermal conductivity of the nanowires is strongly reduced compared to the SiCbulk value. In our approach only the phonon contribution to the heat flow is considered,neglecting any electronic components. We investigate the dependence of the thermalconductivity on the wire cross section and consider the influence of different wire surfaceson the thermal transport.

Comparative study between continuum and atomistic approaches of liquid flow through a finite length cylindrical nanopore

Steady state pressure driven flow of liquid argon through a finite length cylindrical nanopore was investigated numerically by classical Navier-Stokes (NS) hydrodynamic models and nonequilibrium molecular dynamics (MD) simulations. In both approaches, the nanopore was nominally 2.2 nm in diameter and 6 nm long. For the MD simulations, the intermolecular properties of the walls were specified independently from the liquid. Comparisons between the approaches were made in terms of the gross feature of total flow rate through the nanopore, as well as the more refined considerations of the spatial distributions of pressure, density, and velocity. The results showed that for the NS equations to predict the same trends in total flow rate with increasing pressure difference as the MD simulation, submodels for variations in density and viscosity with pressure are needed to be included. The classical NS boundary conditions quantitatively agreed with the flow rate predictions from MD simulations only under the condition of having a neutral-like solid-liquid interaction. Under these conditions, the NS and MD models also agreed well in streamwise distributions of pressure, density, and velocity, but not in the radial direction.

Towards Multiscale Modeling of Metals via Embedded Particle Computer Simulation

The embedded atom method is adapted to study solid friction and the mechanical behavior of a model metal which incorporates the effect of electronic glue in its structure. The elastic properties of real metals are reproduced by a set of basic model potentials as revealed by analytic considerations. A slightly modified version of a classical nonequilibrium molecular dynamics computer simulation is employed to study the dynamics and structural changes of the model metal undergoing a process of solid friction and an uniaxial compression in order to analyze, e.g., plastic yield, transient friction coefficients, and the underlying structure. Under the appropriate choice of parameters, the model turns out to also be applicable for studying multiscale structures in porous metals.

Thermal conductivity of uranium dioxide by nonequilibrium molecular dynamics simulation

The thermal conductivity of ${\mathrm{UO}}_{2}$ pellet, which is used as nuclear fuel, was calculated using the nonequilibrium classical molecular dynamics method by Evans and Morriss. The result of calculation from 300--3000 K obtained presents the same tendency as experiments below 2400 K. Above 2400 K, a different tendency was observed in which the electron conduction was not negligible. The thermal conductivity using the nonequilibrium molecular dynamics method was calculated with about 1/10 number of simulation steps compared with the equilibrium molecular dynamics simulation. It was found that the nonequilibrium molecular dynamics simulation is quite effective.

Electronic spectra from molecular dynamics: a simple approach

Abstract : A method is illustrated for computing the contours of electronic absorption bands from classical equilibrium or nonequilibrium molecular dynamics (or equally for equilibrium systems from Monte Carlo or explicit integration over coordinates). The inputs to the calculations are the potential energy curves for the different electronic states and the electronic transition dipole moments between the states as functions of nuclear coordinates. A simple quantum correction by temperature scaling is demonstrated for the thermal equilibrium case. A test is carried out for the I2 visible absorption spectrum involving transitions from the ground X 0+ sub G(1 sigma) to the excited A 1 sub u(3 Pi) 0+ sub u (3 Pi) and B u (II) states, for thermal equilibrium gas phase I2. The electronic band contours are computed and shown to be remarkably similar to the measured contours.