Amorphous carbon at low densities: An ab initio study. (May 2017)

• Record Type: Journal Article
• Authors: Bhattarai, Bishal; Drabold, D.A.
• Is Part Of: Carbon. Volume 115(2017)
• Page Start: 532
• Page End: 538
• Publication Date: 2017-05
• Subjects: Ab initio -- Low density -- Amorphous carbon -- Phonons -- Specific heat; Carbon -- Periodicals; Carbone -- Périodiques; Koolstof; Toepassingen; Electronic journals; 546.681
• DOI: 10.1016/j.carbon.2017.01.031
• Languages: English
• ISSNs: 0008-6223

Abstract

Abstract: In this paper, we present new computer models of low-density amorphous carbon, and study the structural, electronic and vibrational properties all based upon plane-wave density functional methods. The static structure factor and real space pair-correlation function is in agreement with available experimental data. We observe chains of sp bonded carbon in the models, along with sp 2 and sp 3 structures in varying concentrations. These models provide atomistic insight into the microstructure of the system, delineating variation in bonding ( s p 2, s p 3 and s p ) preferences as a function of density. For these low densities, the vibrational density of states is computed for the first time, along with localization of modes and the specific heat with comparison to experiments. We contrast the amorphous three dimensional networks with amorphous graphene, which bears a striking similarity in the radial distribution functions, but shows a distinct signature in the vibrational density of states. The vibrational modes are analyzed and discussed, and animations of particularly interesting modes are provided as Supplementary Material. The modes are generally well extended, but are more complex than simple molecular pictures that are sometimes invoked, in some cases even revealing mixing among modes of different type. Graphical abstract: Structure of low-density amorphous carbon from accurate ab initio computations. Left: 1.50 gm/cc, Right: 0.92 gm/cc. Red atoms are sp bonded, grey sp 2 and blue sp 3 (periodic boundary conditions are employed). Note the appearance of sp conformations, especially at the lower density.