Model calculation for the tunnel current from a tungsten tip to a Ni(100) surface with a chemisorbed oxygen atom

The tunnel current between a Ni(100) surface with a chemisorbed oxygen atom and a tip described by a single tungsten atom chemisorbed on a W(110) surface is calculated for different distances. The calculations are based on a model Hamiltonian and allow for tip–surface interaction. At small surface–tip separations (≤6 A) a negative corrugation is found, i.e., Oad induces a dent in the constant current contours, in contrast to the contours of total charge density and that at EF. At larger distances they all exhibit a positive corrugation with maxima at the position of the Oad.