1. Department of Mathematics and Computer Science, Freie Universität Berlin, Arnimallee 6, 14195 Berlin, Germany
2. Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305, USA
3. Department of Biochemistry and Molecular Biology, Gordon Center for Integrative Science, The University of Chicago, Chicago, Illinois 60637, USA
4. School of Mathematical Sciences, Tongji University, Shanghai 200092, People’s Republic of China
5. Department of Chemistry, Rice University, 6100 Main St., Houston, Texas 77005, USA