Small rings and amorphous tetrahedral carbon

Abstract

We apply first-principles density-functional calculations to study strain in dense amorphous tetrahedral carbon (a-tC). While the large strain present in small-ring structures, particularly three-member rings, could argue against their existence in a-tC, we demonstrate, based on energetic arguments, that strained small ͑threeand four-member͒ rings are plausible topological microstructural elements. We present two bulk carbon structures made up entirely of fourfold-coordinated atoms: the first with every atom in one three-member ring, the second with every atom in one four-member ring. Calculations show these bulk ring structures are relatively low in energy, only 0.37 and 0.23 eV/atom above diamond, respectively. This computed strain energy is much less than that present in recent models for a-tC. We examine properties of these structures with the intention to provide benchmark calculations for more approximate models, and to investigate the impact small rings might have on the properties of a-tC. We use a recently developed linear-response algorithm to compute phonon spectra for these ring structures.

Compressed carbon nanotubes: A family of new multifunctional carbon allotropes

“…As a consequence, a great number of metastable carbon structures can be produced by compressing small SWCNTs in our simulations. Some previously proposed structures, such as 3D (2,2)-II (Bct-C 4 36), 3D (2,2)-III (Cco-C 8 25), 3D (5,0)-III37, and 3D (3,3)-I38, have been identified along with more new structures. The transition pressures for small ( n ,0) SWCNTs are usually less than 20 GPa, whereas those for small ( n , n ) SWCNTs usually exceed 20 GPa.…”

Raman Spectroscopy of Amorphous Carbon

“…One possibility is that the three-coordinated carbon atoms are assembled into chains which have conjugated n;-bonding. This possibility is supported by theoretical simulation [4,6] and measurements of electronic transport [ I 41, which suggest an average chain length of 13 atoms. Polyvinyl chloride (PVC) is a polymer which spontaneously generates conjugated polyene chains when it degrades by evolution of hydrogen chloride:…”

“…Fullerenes and nanotubes [I61 include these types of rings, with the sixmembered components forming flat sheets and the five-and seven-membered components providing curvature. These complex structures may include tens to hundreds of carbon atoms in sheets or ribbons, which may be too large to model with simulation protocols that use 100 -300 atoms per unit cell [4][5][6]. While no experimental confirmation of the presence of n;-bonded rings exists, theoretical calculations [ I 71 have predicted the Raman frequencies of five -to seven-membered, n;-bonded carbon rings.…”

Global search for low-lying crystal structures using the artificial force induced reaction method: A case study on carbon

“…Furthermore, many stable structures have been predicted theoretically. M-carbon, [313,324] 8-tetra(2,2) tubulane [127] (or bct C 4 [293,329]) or other names [132,288,305,308,332,334,348] ) Cco-C 8 [343] (or Z-carbon [345] ), and so forth have been predicted recently from first principles. [2] R. C. DeVries, Ann.…”