Green's function calculation of Ballistic Electron Emission Microscopy currents (BEEM v2.1)

We describe the FORTRAN-90 program BEEM v2.1 for the computation of real an d reciprocal space currents in Ballistic Electron Emission Microscopy (BEEM ), and Spectroscopy (BEES). Based on a LCAO Hamiltonian, the equilibrium on e-particle Green's functions of a semi-infinite crystal are obtained using a decimation technique. By means of Keldysh's formalism, the STM tip is cou pled to this crystal, and expressions for BEEM currents in real and recipro cal space are obtained. Finally, a Dyson-like equation and a self-consisten t charge neutrality condition are applied to incorporate reconstructed or r elaxed layers in the surface region. Running demos for Au and CoSi2 are pro vided. (C) 2000 Published by Elsevier Science B.V. All rights reserved.