1. Laboratory for Atomistic and Molecular Mechanics (LAMM) Massachusetts Institute of Technology Cambridge MA 02139 USA
2. Department of Civil and Industrial Engineering University of Pisa Pisa 56122 Italy
3. Department of Surgical Medical Molecular Pathology and Emergency Care University of Pisa Pisa 56124 Italy
4. Department of Chemistry Photonics and Energy Research Laboratory University of Texas Rio Grande Valley Edinburg TX 78539 USA