To eliminate the undesirable contacts including overlapping and close contact, a 10,000 step energy minimization was adopted. After this stage, a simulated NVT annealing stage that consisted of ten annealing cycles wherein the temperature was ramped from 300 K to 1000 K and back to 300 K in 20 K intervals during each cycle, with NVT-MD at each interval that lasted for 100 ps with a time step of 1.0 fs. This simulated annealing stage was then followed by another an NPT annealing pro- cedure. Generally, there are mainly two methods to judge the equilibrium: (1) temperature equilibrium,requiring that the standard deviation is less than 10%; (2) energy equilibrium, requiring that energy is constant or fluctuates up and down along the constant value. As showed in Figs. 2 and 3, the temperature and energy of the system met the above equilibrium standard, indicating that the system reached equilibrium during 1000 ps simulation time, but one never knows if the simulation was continued for another 1000 ps whether a new energy might not be reached, owing to the difficulty of minimising a long chain.