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Manuscript Title: Green's function calculation of Ballistic Electron Emission Microscopy currents (BEEM v2.1).
Authors: K. Reuter, P.L. de Andres, F.J. Garcia-Vidal, D. Sestovic, F. Flores, K. Heinz
Program title: BEEM
Catalogue identifier: ADLR_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 127(2000)327
Programming language: Fortran.
Computer: Alpha DEC 3000/400.
Operating system: OSF1 DEC-Unix v4.0.
RAM: 32M words
Word size: 64
Peripherals: disc.
Keywords: Solid state physics, Ballistic electron, Emission microscopy, Green's functions, Decimation, Layer-doubling, Surface electronic, Structure.
Classification: 7.2.

Nature of problem:
We describe the Fortran-90 program BEEM v2.1 for the computation of real and reciprocal space currents in Ballistic Electron Emission Microscopy (BEEM), and Spectroscopy (BEES) [1-4].

Solution method:
Based on a LCAO Hamiltonian, the equilibrium one-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 coupled to this crystal, and expressions for BEEM currents in real and reciprocal space are obtained. Finally, a Dyson-like equation and a self-consistent charge neutrality condition are applied to incorporate reconstructed or relaxed layers in the surface region.

Running time:
The test run took about 1 hr for Au and about 6 hrs for CoSi2 (once the decimation is stored, the run takes around 0.5-0.6 hrs for both Au and CoSi2).

[1] F.J. Garcia-Vidal, P.L. de Andres and F. Flores, Phys. Rev. Lett. 76, 807 (1996).
[2] P.L. de Andres, F.J. Garcia-Vidal, D. Sestovic and F. Flores, Phys. Scripta T66, 277 (1996).
[3] K. Reuter, P.L. de Andres, F.J. Garcia-Vidal, D. Sestovic, F. Flores and K. Heinz, Phys. Rev. B 58, 14036 (1998).
[4] K. Reuter, F.J. Garcia-Vidal, P.L. de Andres, F. Flores and K. Heinz, Phys. Rev. Lett. 81, 4963 (1998).