Open-boundary cluster model implemented in first-principles calculations for electronic excited states of an adsorbate-surface system

Our recently developed open-boundary cluster model (OCM), which allows us to calculate electronic states of a semi-infinite adsorbate-surface system with a finite-small cluster, has been implemented in first-principles calculations to investigate excited states of a real system of a low-coverage Cs/Cu(111). The first-principles calculations are based on a real-space density functional theory (DFT) approach, and the Cs/Cu(111) system is reasonably represented in terms of a cluster of CsCu13 within the OCM approach. An absorption spectrum and the lifetime of excited states of the system are calculated successfully within the linear-response approximation, and the computed results qualitatively agree with experimental observations. Such excited properties are difficult to calculate by using a conventional cluster model (CCM) approach. Despite these advantages, the OCM-DFT approach requires a computational cost almost identical to the cost of CCM.