1. Department of Computer Science, Texas Tech University, Lubbock, Texas 79409-3104, United States
2. Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, United States
3. Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel
4. Dipartimento di Chimica, Università degli Studi di Milano, via Golgi 19, 20133 Milano, Italy