[1] EMORY UNIV, CHERRY L EMERSON CTR SCI COMPUTAT, ATLANTA, GA 30322 USA
[2] UNIV AUTONOMA BARCELONA, DEPT QUIM, UNITAT QUIM FIS, E-08193 BELLATERRA, BARCELONA, SPAIN
[3] UNIV MONTPELLIER 2, UMR 5636, LAB STRUCT & DYNAM SYST MOL & SOLIDES, F-34095 MONTPELLIER 5, FRANCE