1. Department of Physics, University of Massachusetts, Amherst, Massachusetts 01003, Department of Physics, University of North Texas, Denton, Texas 76203, INEST Group Postgraduate Program and Research Center, Philip Morris USA, Richmond, Virginia 23234, Harrington Department of Bioengineering, Arizona State University, Tempe, Arizona 85287, and NIST Center for Theoretical and Computational Nanosciences, Gaithersburg, Maryland 20899