The diamond sample with its heavily damaged central part caused by the energetic displacement of 12 atoms at T = 0 K, as described above, was heated to 3000K and its structural evolution was followed by the MD procedure. The annealing was also applied to a sample damaged by the displacement of only one atom, in order to study the influence that the density of defects has on the structure obtained after annealing. Heating the sample was achieved by the input of initial random atomic velocities according to the Boltzman distribution. Periodic boundary conditions were used, and the atomic velocities of the four outermost layers were rescaled at each step of the computation to maintain the temperature at 3000 K during the entire simulation. These boundary atoms are far enough from the damaged region so that the dynamic behavior of the atoms inside the damage region was not affected by the rescaling procedure.
This annealing process effectively simulates an annealing process under constant volume and temperature, i.e. under high internal pressure. The sample was annealed during 20 ps, and averages of the atomic coordinates were computed for every 0.25 ps interval (a typical period of oscillation in diamond is 0.025 ps). This procedure was repeated six times, changing only the initial random atomic velocity vectors. Our final estimates of the statistical properties of the samples obtained are averages over the six different configurations. It has to be mentioned that similar qualitative results were obtained by applying a Nose-Hoover thermostat .
The slightly damaged sample was also annealed at 3000 K during 20 psec, using the same procedure as that discribed above. However, to speed up the structural changes induced by annealing, a temperature of 4000 K (below the melting temperature) was also applied. This led to very appealing results.