STM image by the Tersoff-Hamann scheme

Scanning tunneling microscope (STM) image can be obtained by the Tersoff-Hamann scheme [48]. The method is nothing but calculation of partial charge density in an energy window measured from the chemical level. The calculation of the partial charge density is performed by the following keywords:

   partial.charge                 on       # on|off, default=off
   partial.charge.energy.window   0.0      # in eV

where the second keyword defines an energy window (in eV) measured from the chemical potential (a plus value means conduction band and negative valence). Since the calculation of the partial charge density is performed during calculation of the density of states (DOS), the following keywords have to be specified as well:

  Dos.fileout                  on        # on|off, default=off
  Dos.Erange              -20.0  20.0    # default = -20 20
  Dos.Kgrid                  5 5 5       # default = Kgrid1 Kgrid2 Kgrid3

After the calculation with the keywords, you will get *.pden.cube which can be used for the STM simulation within the Tersoff-Hamman approximation. As an example, a simulated STM image of a graphene layer is shown in Fig. 40.

Figure 40: Simulated STM image of a graphene layer, where partial.charge.energy.window of 2 eV was used in the calculation, and the input file is 'Graphene_STM.dat' in the direcoty 'work'. The cube file 'Graphene_STM.pden.cube' was visualized with an isovalue of 0.0001 by a software WSxM [87].