New electron states that float on semiconductor and metal surfaces

We report first-principle electronic-structure calculations using the local density approximation in the density functional theory for Si(1 0 0) and Al(1 0 0) surfaces. We find a novel class of surface electron states that are distributed not near atomic arrays but float around with the maximum amplitudes being substantially separated from matters. We also find that the origin of the unusual character is quantum spill of electron density from matters and exchange-correlation effects among electrons.