https://doi.org/10.1351/goldbook.14083
Zero-dimension site (atom, ion, or interstitial position) at a regular surface.
Note: It can be a photocatalytic centre (site) in the ground (not active) state in some particular cases of heterogeneous photocatalysis as, e.g., in the case when pre-physisorbed entities trap photocarriers in the course of the photocatalysed reaction.