Simple-cubic three-dimensional C60 polymer

We study the structural phase transition of orientationally ordered simple-cubic (sc) C60 under pressure by using the tight-binding molecular dynamics method. We investigate the system under five pressure values, 10, 20, 30, 40, and 50 GPa. Under 10 and 20 GPa, sc C60 transforms into a new sc three-dimensional (3D) C60 polymer. We study the structural stability as well as the electronic properties of this sc 3D C60 polymer using the density-functional total-energy calculation with the local-density approximation, and this new sc 3D polymer phase is predicted to be highly stable. Interestingly, the lattice constant of this new sc 3D polymer phase is found to be close to those of both the face-centered-cubic (fcc) 3D phase of Yamanaka et al. [J. Am. Chem. Soc. 130 (2008) 4303] and that of Mezouar et al. [Phys. Rev. B 68 (2003) 193414]. In addition, the material is predicted to be a semiconductor. Moreover, it is even found from simulated structure factors for this new sc 3D polymer phase that this new sc 3D polymer phase might satisfy the extinction rule of fcc when the antiphase boundary defects exist in the crystal, indicating that this phase can be a candidate for one of main phases in the experimental samples.