Cohesive energy graphite

Because the cohesive energy of the fullerene Cyo is —7.29 eV/atom and that of the graphite sheet is —7.44 eV/atom, the toroidal forms (except torus C192) are energetically stable (see Fig. 5). Finite temperature molecular-dynamics simulations show that all tori (except torus Cm2) are thermodynamically stable. 

The value 125 kcal/mol represents an upper bound to the cohesive energy per carbon atom in graphite, since the interaction between iayers in the buik has not been accounted for. Given the reiativeiy large distance and the physicai properties of graphite, the interiayer interaction energy is estimated to be < 5 kcai/mol. 

This leaves us with a computed resuit in iess than satisfactory agreement with the experimental value of about 170 kcal/mol(57). The neglect of electron correlation and the limited basis set used are the most important sources of the discrepancy. In a previous study on monolayer graphite(56), basis set effects were found to lead to a significant underestimation of the cohesive energy. 

The cohesive energy per carbon atom in a poly-yne ring is only 99.1 kcal/mol, clearly lower than the value in Cc. Anticipating a long and complicated route of formation when starting from graphite, in does not seem likely that any of the larger clusters observed experimentally would have a linear or cyclic chain structure. 

The Wigner Disease . Wigner had contributed to the quantum mechanics of solids with his calculations, together with Seitz, of the cohesive energy of crystals. It was therefore natural for him, especially with his background in chemistry, to worry about the effect of neutron bombardment on the properties of graphite. He, together with F. L. Friedman and F. Seitz, estimated the number of displacements that a moderator atom would suffer in the course of... 

Some of the first molecular mechanics calculations on CNTs were reported by Robertson et al. in a paper published in 1992. By computing the energies for a series of SWCNTs with various diameters (D < 0.9 mn) and chiralities, these authors found that the strain energy per carbon atom (relative to an unfolded, planar sheet of graphite) varied as Several years later, molecular mechanics calculations by Tersoff and Ruoff demonstrated that the energy of interaction per unit surface area between adjacent nanotubes (and consequently, the cohesive energy of a CNT bundle) varied as This dependence was verified in... 

FIGURE 4.8 Molecular model used in the calculation of the cohesive energy of graphite. 

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