[1] Univ Complutense, Fac Quim, Dept Quim Fis, E-28040 Madrid, Spain
[2] Univ Politecn Madrid, ETS Ingenieros Montes, Dept Quim & Bioquim, E-28040 Madrid, Spain
[3] CSIC, Inst Matemat & Fis Fundamental, E-28006 Madrid, Spain
[4] Univ Oxford, Phys & Theoret Chem Lab, Oxford OX1 3QZ, England