1. Institute for Computational Physics, Universität Stuttgart, Allmandring 3, 70569 Stuttgart, Germany
2. Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Max-von-Laue-Str. 3, 60438 Frankfurt, Germany
3. Argonne National Laboratory, 9700 S. Cass Avenue, Building 240, Argonne, Illinois, United States
4. Dipartimento di Fisica, ISC-CNR, Istituto Sistemi Complessi, Università Sapienza, P.le A. Moro 2, 00185 Rome, Italy