1. Computer Science Faculty, University of Coruña, E-15071 A Coruña,
Spain
2. Department of Physical Chemistry
and Center for Research in Biological Chemistry and Molecular Materials
(CIQUS), University of Santiago de Compostela, E-15782 Santiago de Compostela, Spain
3. Department of Mathematics, Technical University of Denmark, DK-2800 Kongens Lyngby,
Denmark
4. Department of Chemistry
and
Biochemistry, University of California,
Los Angeles, California 90095-1569, United States