Theory of the scanning tunneling microscope: Xe on Ni and Al

We present a theory for the scanning tunneling microscope (STM) current based on a Keldysh Green function formalism. In our formalism, we solve self-consistently an ab initio linear combination of atomic orbitals Hamiltonian within a local density formalism. Total energy calculations for xenon deposited on metal surfaces are performed to obtain the equilibrium position, and the Green functions needed to compute the current are obtained at the same time. Structural and nonstructural effects that can influence the correct interpretation of experimental STM results are studied. We find good agreement between our calculations and experimental images taken under highly controlled conditions, and we conclude that STM images should be analyzed by comparing iteratively the theory and the experiment, much in the same way as it is usually done for other surface sensitive techniques Like low-energy electron diffraction, photoelectron diffraction, surface-extended x-ray-absorption fine structure spectroscopy, etc.