This page describes how to generate, using Fireball, the tip_e_str.inp with the retarded and advanced green functions and the density of states (DOS) for the STM program .
First, we need to obtain SCF-solution for particular geometry. Once we have it, we need to switch on these options:

  ifixcharge = 1  
  iwrtdos = 1

Simulation parameters are defined in two additional files:

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''dos.optional''
This file defines basic parameters of the DOS calculation.

       1.00000              ! ratio of lattice (for fractional coordinates, if xyz are in Angstroms maintain 1.000)
       1   5                ! natom_beg,natom_end (initial and final atom for the DOS calculation)   
     401                    ! number of energies (number of energies in the DOS calcuation)
  -12.0    0.05             ! first energy (initial absolute energy (fireball's value is the Fermi Level) and energy step  
       1                    ! 1/0 yes/no write the tip_e_str.inp file for the DOS
      -4.01  4.01           ! minimun and maximum energy limit for writing the green function in the tip_e_str.inp file
       0.05                 ! imaginary part for the green function in the DOS calculation

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One comment related with the minimum and maximum energy limits. Normally, we are interested in the range 2eV bellow and above the Fermi Level, but calculating a bigger range of DOS. These parameters give us the opportunity to do both things together: dos calculation and tip_e_str.inp fie generation. As an example we can consider a system with a FL=-2.0 eV and we want to generate the file from -2+FL to FL+2 doing the calculation of the complete DOS from -10 to +10 with an energy step of 0.05. The corresponding file is showed above. (Take a look to the minimum and maximum vales a little bit larger to avoid numerical bad effects).