Theoretical Biology and Biophysics Group, Los Alamos National Laboratory, New Mexico, United States of America.|BioSciences Division, Los Alamos National Laboratory, New Mexico, United States of America.|BioSciences Division, Los Alamos National Laboratory, New Mexico, United States of America.|Department of Chemistry, University of Chicago, Illinois, United States of America.|Theoretical Biology and Biophysics Group, Los Alamos National Laboratory, New Mexico, United States of America.