Schematic representation of the -graphene composite. (a) The complex is positioned with a Cp ligand parallel to and at a fixed distance from the surface of the graphene sheet. (b)–(d) provide projection views of the “stack,” “bridge,” and “hexagon” positions, respectively.
Interaction energy curves [ (Å) vs (eV)] for (a) -graphene (“stack” configuration) and (b) -graphene (“bridge” configuration).
(Color online) Optimized structure for (‖). Radial deformation of the SWNT is visible in the cross sectional view of this composite.
(Color online) Electronic band structures for (a) an isolated (17,0) SWNT, (b) (‖), and (c) (⊥). Valence and conductance bands of the isolated (17,0) SWNT are superimposed (red dashed lines) on (b) and (c) for comparative purposes.
(Color online) Electronic band structures for (a) an isolated (12,0) SWNT, (b) (‖), and (c) (⊥). Valence and conductance bands of the isolated (12,0) SWNT are superimposed (red dashed lines) on (b) and (c) for comparative purposes.
Contour plots of (the first derivative of the electron density) for (a) (‖) and (b) (⊥).
Electronic band structures for (a) (⊥), (b) (‖), (c) (‖), and (d) (⊥). In band structure plots (a)–(d) the Fermi level is shifted to . indicates the SOMO of and indicates the conductance band of the SWNT. Band structures (a)–(d) are placed in order of increasing charge transfer from to the SWNT.
Reference configuration and cutoff radii (a.u.) of the H, C, Fe, and Co pseudopotentials. Ionic pseudopotentials were generated for Fe and Co, while neutral pseudopotentials were generated for C and H.
Calculated average bond lengths (Å) and angles for and (standard deviations are provided in parentheses). represents the spin where is equivalent to one unpaired electron (upe). The dihedral angle is measured in the plane of the Cp ring. The angle represents the angle between the metal-ring centroid normals. Symmetry of the input structure for each organometallic complex is denoted as either “A” (eclipsed) or “B” (staggered).
Equilibrium structures [average bond lengths and angles ( between the metal-ring centroid normals; ring dihedral) for , and equilibrium Cp-graphene separation ] and formation energies (, , , ; units eV) for -graphene composites calculated in both total energy [geometry optimization (GO)] and single point (SP) calculations. The Mulliken charge, of , and the spin density (number of unpaired electrons) for the metallocene in these composites are also provided.
Summary of the results obtained from first principles pseudopotential calculations on composites. The symbols ⊥ and ‖ indicate a perpendicular and parallel orientation of the axis of with the major axis of the SWNT. SP indicates that the equilibrium structure was located from a series of single point calculations (rather than a total energy optimization). Structural information for these composites includes the equilibrium Cp-SWNT separation , average CH-SWNT distance, and the percentage radial distortion (r.d.) of the SWNT. and quantify the perturbation of and the SWNT, respectively, from their equilibrium structures. is the overall formation energy (BSSE-corrected) of the composite. The Mulliken charge of in these composites is also provided.
Calculated spin density for the metallocene and nanotube fragments in .
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