Table 1 Calculated lattice parameters a and c (in Å), equilibrium density (ρ in g/cm3), bond length (d in Å) and cohesive energy (Ecoh in eV) of H18 carbon in comparison with those of diamond, graphite and some other carbon allotropes.

From: H18 Carbon: A New Metallic Phase with sp2-sp3 Hybridized Bonding Network

Structure Space group Method a (Å) c (Å) ρ (g/cm3) d (Å) Ecoh (eV/atom)
Diamond LDA 3.535   3.611 1.531 8.927
   PBE 3.572   3.501 1.578 7.780
   Exp.22 3.567   3.520 1.544  
Graphite LDA 2.446 6.594 2.335 1.412 8.918
   PBE 2.467 8.145 1.859 1.424 7.900
   Exp.21 2.460 6.704 2.280 1.420  
T6 LDA 2.567 5.937 3.059 1.522, 1.331 8.416
   PBE37 2.600 6.000 2.952 1.540, 1.340  
BC8 LDA 4.426   3.681 1.446, 1.611 8.239
   PBE 4.477   3.556 1.456, 1.631 7.082
Rh6 LDA 6.914 3.277 2.647 1.469, 1.357 8.441
   PBE 6.885 3.585 2.439 1.491, 1.357 7.400
H18 LDA 7.056 2.563 3.248 1.310–1.609 8.547
   PBE 7.125 2.605 3.135 1.317–1.631 7.269