Green's function calculation of Ballistic Electron Emission Microscopy currents (BEEM v2.1). K. Reuter, P.L. de Andres, F.J. Garcia-Vidal, D. Sestovic, F. Flores, K. Heinz.

Title of program: BEEM
Catalogue identifier: ADLR
Ref. in CPC: 127(2000)327
Distribution format: gzip file
Operating system: OSF1 DEC-Unix v4.0
High speed store required: 32MK words
Number of bits in a word: 64
Peripherals Required: disc
Number of lines in distributed program, including test data, etc: 17633
Programming language used: Fortran
Computer: Alpha DEC 3000/400

Nature of physical 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].

Method of solution
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.

Typical 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).