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

Structures and incremental binding enthalpies were determined for the M+(H2O)(n) ionic clusters, M = Cu, Ag, Au; n = 1-4 (5 for Cu) using correlated ab initio electronic structure methods. The effects of basis set expansion and high-level correlation recovery were found to be significant, in contrast to alkali and alkaline earth cation/water complexes, where correlation of the d electrons is unimportant. The use of a systematic sequence of one-particle basis sets permitted binding enthalpies in the complete basis set limit to be estimated. Overall, the best theoretical binding enthalpies compared favorably with the available experimental data for copper and silver. No experimental data is available for gold/water clusters. The largest deviation was noted for Ag+(H2O)(2), where theory predicts an incremental binding enthalpy of 28 kcal/mol and experiment measures similar to 25 kcal/mol. However, the uncertainty associated with one of the two experimental values is quite large (+/-3 kcal/mol) and almost encompasses the theoretical result. Results were also obtained with the more cost-effective 6-31 + G* basis set and calibrated against the estimated complete basis set limits. (C) 1999 American Institute of Physics. [S0021-9606(99)30103-3].