Structures and binding enthalpies of M+ (H2O)(n) clusters, M=Cu, Ag, Au

Structures and incremental binding enthalpies were determined for the M+(H2 O)(n) ionic clusters, M = Cu, Ag, Au; n = 1-4 (5 for Cu) using correlated a b initio electronic structure methods. The effects of basis set expansion a nd high-level correlation recovery were found to be significant, in contras t to alkali and alkaline earth cation/water complexes, where correlation of the d electrons is unimportant. The use of a systematic sequence of one-pa rticle basis sets permitted binding enthalpies in the complete basis set li mit to be estimated. Overall, the best theoretical binding enthalpies compa red favorably with the available experimental data for copper and silver. N o experimental data is available for gold/water clusters. The largest devia tion was noted for Ag+(H2O)(2), where theory predicts an incremental bindin g enthalpy of 28 kcal/mol and experiment measures similar to 25 kcal/mol. H owever, the uncertainty associated with one of the two experimental values is quite large (+/-3 kcal/mol) and almost encompasses the theoretical resul t. Results were also obtained with the more cost-effective 6-31 + G* basis set and calibrated against the estimated complete basis set limits. (C) 199 9 American Institute of Physics. [S0021-9606(99)30103-3].