1. Laboratory for Atomistic and Molecular Mechanics (LAMM), Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA.
2. Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA.
3. Department of Engineering Science, National Cheng Kung University, No.1, University Road, Tainan City 701, Taiwan.
4. Center for Computational Science and Engineering, Schwarzman College of Computing, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA.
5. Center for Materials Science and Engineering, 77 Massachusetts Ave., Cambridge, MA 02139, USA.