1. Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom
2. Department of Mechanical and Aerospace Engineering, Sapienza University, 00184 Rome, Italy
3. Ames Research Center, KBR, Inc., Moffett Field, California 94035, United States
4. Computational Biological Center, IBM Thomas J. Watson Research, Yorktown Heights, New York 10598, United States
5. Applied Chemicals and Materials Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States