Molecular dynamics simulations of diamond-like carbon overcoat

• Main Author: Lim, Chu Ern.
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/54014
• Institution: Nanyang Technological University

Molecular dynamics (MD) simulation of diamond-like carbon (DLC) structure was conducted using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). MD simulation was done with the aim to obtain the highest sp3 bonds content through the implementation of different factors such as interaction potentials, cooling rates, thermostats and densities. The system with 1000 carbon atoms simulated in a simulation box were studied using Adaptive Interatomic Reactive Empirical Bond Order (AIREBO) potential and the Reactive Force Field (ReaxFF) potential models. Two different thermostats were used to control the temperature during the simulations: Berendsen and Langevin. All simulations were repeated with three different densities of 3.0g/cm3, 3.3g/cm3 and 3.53g/cm3 and two cooling rates of 1015K/s and 1016K/s. AIREBO potential is the improved version of Reactive Empirical Bond Order (REBO) potential. AIREBO potential improves the REBO potential’s repulsive and attractive pair interaction function by including long range atomic interaction, torsional term and non-bonded interactions. ReaxFF potential made use of two general relationships which lead to the proper dissociation of bonds of separated atoms ‒ firstly between bond order and bond energy, and secondly between bond distance and bond order. Berendsen thermostat is neither a canonical nor a stochastic thermostat, while Langevin thermostat is both canonical and stochastic. Langevin thermostat uses frictional drag force and random force of the system to ensure the desired temperature of the system is achieved. On the contrary, Berendsen thermostat uses its kinetic energy to ensure that the temperature matches the desired temperature. Four observations have been made from the MD simulation results. Firstly, results have shown that the use of ReaxFF potential displayed better results as compared to that of AIREBO potential. Secondly, the use of Langevin thermostat produced slightly more sp3 bonds as compared to Berendsen thermostat. Thirdly, results have shown that the amount of sp3 bonds achieved increases with increasing density used. Finally, the amount of sp3 bonds produced using cooling rates of 1015 K/s and 1016 K/s does not differ much.