Surface barrier in metals: A new model with application to W(001)

A new model of the surface barrier at a metal surface is presented. It is one dimensional, has two adjustable parameters $z_0$, the location of the image plane, and $\lambda$, which determines the length scale of the transition from vacuum to bulk), and its form is suggested by the results of self-consistent electronic-structure calculations for a five-layer film of W(001) described here. The optimum form for electrons with incident energies below 10 eV is determined by comparison with available low-energy-electron-diffraction data from W(001).