The interaction of gold clusters with methanol molecules: Ab initio molecular dynamics of Au⁺ _nCH₃OH and Au_nCH₃OH

Structural, dynamical, and electronic properties of adducts obtained by adsorbing one methanol molecule onto charged and neutral gold clusters, Au⁺ _n-CH₃OH and Au_n-CH₃OH, are investigated using Car-Parrinello ab initio molecular dynamics as a function of the cluster size n. The absorption process occurs by the formation of a Au(Black star)-0 coordination bond to one particular gold atom Au(Black star) without altering the structure of the underlying cluster. This chemical bond is much stronger for the charged metal clusters Au⁺ _n than for the neutral analogs Au_n. In the charged case, the C-O stretching vibration of the interacting methanol molecule is found to increase discontinuously as the underlying cluster structure changes from two-dimensional to three-dimensional. The weaker C-O bond in the neutral species however has "insufficient strength" to be sensitive to changes in coordination number and cluster structure. This leads to a constant C-O stretching frequency as the size of the cluster increases, including the regime where the Au_n cluster changes from planar to three-dimensional.