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At finite temperature, the silver-cluster catalysts could have transient meta-stable structures with spin states higher than those of zero kelvin stable structures (singlets for an even number of silver atoms). These transient structures could be crucial in activating adsorbed species like O$_2$. In this work, the temperature-dependent relative stability of Ag$_n$ and Ag$_n$O$_2$ ($n=4,8$) systems are simulated at different finite temperatures, by means of replica-exchange ab initio molecular dynamics (REMD) and efficient Boltzmann-reweighting based methods (e.g., Weighted Histogram Analysis Method, WHAM, and multi-state Bennett acceptance ratio estimator, MBAR). The multi-spin-state free energy surfaces are visualized with the help of Sketch-Map [1]. The results show that meta-stable structures and the spin-polarized states can synergistically influence the activation of the adsorbed O$_2$ molecule.
[1] M. Ceriotti, G. A. Tribello, M. Parrinello, J. Chem. Theory Comput. 9 1521 (2013).
