E. R. Hernández

Mechanical Properties, Thermal Stability and Heat Transport in Carbon Nanotubes

Ever since the discovery of carbon nanotubes (CNTs) in the early 1990s, it wasanticipated that these nanostructures would have truly remarkable mechanical andheat-transport properties, given the strength of the carbon-carbon bond withingraphene layers in graphite. Nowadays, there is growing evidence, coming fromboth experimental and theoretical studies, that CNTs do indeed have anoutstandingly high Young’s modulus, high thermal stability and thermalconductivity. In this contribution, we provide an overview of the current stateof knowledge on these properties in CNTs and related nanostructures.

Path integral calculation of free energies: Quantum effects on the melting temperature of neon

The path integral formulation has been combined with several methods to determine free energies of quantum many-body systems, such as adiabatic switching and reversible scaling. These techniques are alternatives to the standard thermodynamic integration method. A quantum Einstein crystal is used as a model to demonstrate the accuracy and reliability of these free energy methods in quantum simulations. Our main interest focuses on the calculation of the melting temperature of Ne at ambient pressure, taking into account quantum effects in the atomic dynamics. The free energy of the solid was calculated by considering a quantum Einstein crystal as reference state, while for the liquid, the reference state was defined by the classical limit of the fluid. Our findings indicate that, while quantum effects in the melting temperature of this system are small, they still amount to about 6% of the melting temperature, and are therefore not negligible. The particle density as well as the melting enthalpy and entropy of the solid and liquid phases at coexistence is compared to results obtained in the classical limit and also to available experimental data.

Path-integral molecular dynamics simulation of diamond

Diamond is studied by path integral molecular dynamics simulations of the atomic nuclei in combination with a tight-binding Hamiltonian to describe its electronic structure and total energy. This approach allows us to quantify the influence of quantum zero-point vibrations and finite temperatures on both the electronic and vibrational properties of diamond. The electron-phonon coupling mediated by the zero-point vibration reduces the direct electronic gap of diamond by 10 %. The calculated decrease of the direct gap with temperature shows good agreement with the experimental data available up to 700 K. Anharmonic vibrational frequencies of the crystal have been obtained from a linear-response approach based on the path integral formalism. In particular, the temperature dependence of the zone-center optical phonon has been derived from the simulations. The anharmonicity of the interatomic potential produces a red shift of this phonon frequency.At temperatures above 500 K, this shift is overestimated in comparison to available experimental data. The predicted temperature shift of the elastic constant c_{44} displays reasonable agreement with the available experimental results.

Path-integral molecular dynamics simulation of 3C-SiC

Molecular dynamics simulations of

Hydrogen and muonium in diamond: A path-integral molecular dynamics simulation

3C\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}

Nanotubes and nanowires: the effect of impurities and defects on their electronic properties

have been performed as a function of pressure and temperature. These simulations treat both electrons and atomic nuclei by quantum mechanical methods. While the electronic structure of the solid is described by an efficient tight-binding Hamiltonian, the nuclei dynamics is treated by the path-integral formulation of statistical mechanics. To assess the relevance of nuclear quantum effects, the results of quantum simulations are compared to others where either the Si nuclei, the C nuclei, or both atomic nuclei are treated as classical particles. We find that the experimental thermal expansion of

Molecular Dynamics Simulations of Nanotube Growth

3C\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}

Using Thermal Gradients for Actuation in the Nanoscale

is realistically reproduced by our simulations. The calculated bulk modulus of

First-principles studies of the diffusion of B impurities and vacancies in SiC

3C\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}

Evolution-operator method for density functional theory

and its pressure derivative at room temperature show also good agreement with the available experimental data. The effect of the electron-phonon interaction on the direct electronic gap of