Article Cite This: J. Chem. Theory Comput. XXXX, XXX, XXX−XXX
pubs.acs.org/JCTC
ReaxFF Molecular Dynamics Simulation for the Graphitization of Amorphous Carbon: A Parametric Study Kejiang Li,*,† Hang Zhang,‡ Guangyue Li,§ Jianliang Zhang,†,# Mohammed Bouhadja,∥ Zhengjian Liu,† Adam Arnold Skelton,○,△ and Mansoor Barati⊥ †
School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, P.R. China Modern Technology and Education Centre, North China University of Science and Technology, Tangshan 063009, P.R. China § College of Chemical Engineering, North China University of Science and Technology, Tangshan, Tangshan 063009, P.R. China ∥ Laboratoire de Physique de la Matière Condensée, Université Picardie Jules Verne, Amiens 80000, France ⊥ Department of Materials Science and Engineering, University of Toronto, Toronto, ON M5S 3E4, Canada # School of Chemical Engineering, The University of Queensland, St Lucia, QLD 4072, Australia ○ Department of Chemistry, University of Liverpool, Liverpool L69 3BX, United Kingdom △ School of Health Sciences, University of KwaZulu-Natal, Durban 4001, South Africa ‡
S Supporting Information *
ABSTRACT: A parametric study of ReaxFF for molecular dynamics simulation of graphitization of amorphous carbon was conducted. The responses to different initial amorphous carbon configurations, simulation time steps, simulated temperatures, and ReaxFF parameter sets were investigated. The results showed that a time step shorter than 0.2 fs is sufficient for the ReaxFF simulation of carbon using both Chenoweth 2008 and Srinivasan 2015 parameter sets. The amorphous carbon networks produced using both parameter sets at 300 K are similar to each other, with the first peak positions of pair distribution function curves located between the graphite sp2 bond peak position and the diamond sp3 bond peak position. In the graphitization process, the graphene fragment size increases and the orientation of graphene layers transforms to be parallel with each other with the increase of temperature and annealing time. This parallel graphene structure is close to the crystalline graphite. Associated with this graphitization is the presence of small voids and pores which arise because of the more efficient atomic packing relative to a disordered structure. For all initial densities, both potential parameter sets exhibit the expected behavior in which the sp2 fraction increases significantly over time. The sp2 fraction increases with increasing temperature. The differences of sp2 fraction at different temperatures are more obvious in lower density at 1.4 g/cm3. When density is increased, the gap caused by different temperatures becomes small. This study indicates that both Chenoweth 2008 and Srinivasan 2015 potential sets are appropriate for molecular dynamics simulations in which the growth of graphitic structures is investigated. and N increases to 8−10. The third stage (1500−2000 °C) corresponds to the release of in-plane defects. A considerable increase in thickness, and then, the coalescence of adjacent columns can be observed due to the disappearance of misoriented single BSU. The fourth stage (>2100 °C) corresponds to the annealing of all distortions. The layers become stiff and perfect. The heteroatoms and both the interlayer and in-plane defects have gradually disappeared, leading to the start of graphite crystal growth. To further understand the carbonization process, molecular dynamics (MD) simulation has been employed to build various
1. INTRODUCTION The structural transformation of carbon (coke or coal char) during heat treatment determines its properties in both ambient and high temperatures. Oberlin et al.1,2 conducted comprehensive high resolution transmission electron microscopy (HRTEM) studies of carbon structure during heat treatment, demonstrating four stages for the change of microtexture during carbonization up to 3000 °C.1,3 The first stage (
