Calculated electronic density of states and structural properties of tetrahedral amorphous carbon

A series of tetrahedral amorphous carbon structures with different microsco pic mass densities was generated by calculations based on the density funct ional theory with a local density approximation and using a method of melti ng-cooling cycles. A detailed investigation of the properties of the simula ted structures has been carried out. particularly, the short-range order, n earest neighbour distances, fractions of sp(1), sp(2) and sp(3) sites, aver age C-C-C bond angles and electronic density of states have been analysed. The simulated structures and calculated properties are in good agreement wi th those obtained by others and with the experimental data. An unexpected o bservation is the presence of planar structures, which are typical for grap hite, in the sample with low density. In addition, the nearest neighbour di stance in the sample with mass density 3.54 g/cm(3) is different from those reported previously. Possibilities to compare the density of states obtain ed from the simulations with the experimental results from scanning tunnell ing spectroscopy and X-ray near edge spectrum are discussed. (C) 2000 Elsev ier Science S.A. All rights reserved.