Properties of adsorbates as open quantum systems

We have recently developed a novel cluster-model approach to investigate adsorbate-surface systems. In our approach, a physically relevant subsystem is described as an open quantum system by considering a model cluster subject to the outgoing-wave boundary condition (OBC) at the edge of the cluster. We refer to this model as an open-boundary cluster model (OCM). Many known disadvantages of the conventional cluster-model approach, in which a model cluster is treated as an isolated system, have been remedied by introducing the OBC, whereas the local picture inherent in cluster models still remains valid. In our present research, the adsorption energy and the electron-transfer rate from adsorbates to surfaces are calculated with the OCM. Their dependences on the adsorption-distance and the Fermi energy are reasonably explained by analyzing the quasi-diabatic energy levels based on the local picture of adsorption.