Density functional theory study of the interaction of carbon monoxide with bimetallic Co-Mn clusters.

Using spin-polarized density functional calculations, we have studied the interaction of carbon monoxide (CO) with bimetallic Co(n)Mn (n = 1-6) and Co(n)Mn(6-n) (n = 0-6) clusters. Various adsorption sites including atop, hollow, and bridge adsorption patterns and different possible spin states are considered. The CO molecule prefers to adsorb at the Co site rather than at the Mn site. Atop adsorption structure is energetically more favored over the hollow and bridge adsorption ones for the bimetallic clusters with an exception of Co(5)Mn. Large adsorption energy is found at Co(3)Mn, Co(2)Mn(4), and Co(3)Mn(3), associating with the relative stability of the bare Co-Mn clusters and the electrostatic interactions as well as adsorption patterns. The activation of the C-O bond and the red shift of the C-O stretching frequency are sensitive to the adsorption sites and high chemical activity is identified for Co(6), Co(5)Mn, and Mn(6) clusters. More interestingly, the adsorption of CO has different influence on the magnetism of the clusters: the magnetic moment remains unchanged for CoMn and Co(2)Mn, while it is reduced by 2 μ(B) for Co(n)Mn (n = 3-6) and Co(n)Mn(6-n) (n = 0-5) and is enhanced by 2 μ(B) for Mn(6) when a CO molecule is loaded to the cluster.