ANALYSIS OF THE THERMAL PROPERTIES OF ZINC OXIDE USING THE ReaxFF REACTIVE FORCE FIELD

Open Access
Author:
Krishnasamy Bharathi, Arvind
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 05, 2010
Committee Members:
  • Adrianus C Van Duin, Thesis Advisor
Keywords:
  • nanowire
  • Zinc Oxide
  • ReaxFF
Abstract:
The objective of this paper is to determine the thermal conductivity of Zinc Oxide nanowire by equilibrium and non-equilibrium molecular dynamics (EMD and NEMD) simulations using the ReaxFF reactive force field [19]. While EMD uses an equilibrated system and statistical averaging; NEMD uses cooling/heating rates in order to calculate the conductivity. The validity of the methods is first verified using Argon as a test case. The thermal conductivity of Argon thus calculated is compared with the results obtained by Bhowmick and Shenoy [69]. We then study the effects of system size using EMD method and effects of periodic boundary conditions - 1D, 2D and bulk variation of conductivity with temperature are analyzed using NEMD simulations. The results obtained compare favorably with those measured experimentally [46][47]. This indicates that the EMD and NEMD methods are reliable alternatives to the traditional Green-Kubo approach [51]; which is traditionally employed in MD-based thermal conductivity determination. In conjunction with ReaxFF, these methods are computationally cheaper than the Green-Kubo method and can be used to determine the thermal conductivity of materials involved in surface chemistry reactions such as catalysis and sintering. The effect of chemistry on the thermal conductivity of Zinc Oxide is studied. Sintering is taken as the chemical process of interest and is simulated using ReaxFF force field for Zinc Oxide [58] in the presence of water. Effect of sintering temperature is also observed. A clear drop in the conductivity of Zinc Oxide due to the formation of hydroxyl grain-boundaries between the different Zinc Oxide clusters is noted. However, this deterioration is smaller when we use higher sintering temperatures. Due to a relatively small number of atoms (960) and the non-homogeneousness of the cluster; (mix of Zinc Oxide and water) the error bars on thermal conductivity are large. This indicates the need for performing larger-scale simulations in order to determine the effect of sintering on thermal-conductivity more accurately.