As an example, we show in Fig. 74 the Berry curvature of graphene. Since the absolute magnitude of Berry curvature is approximately proportional to the square of inverse of bandgap, the large Berry curvature can be seen around K and K' points, where the massive Dirac point appears if we include spin-orbit interaction.

Let us illustrate how the calculation can be performed by using an input file 'Graphene-Chern.dat' stored in the directory 'work'.

SCF calculation

When you perform the SCF calculation for graphene using an input file 'Graphene-Chern.dat' stored in the directory 'work', you need to switch on the keyword 'HS.fileout' as

    HS.fileout      on      #on|off, default=off
After finishing the SCF calculation normally, we may obtain an out file 'Graphene-Chern.scfout'.

Calculation of Chern number and Berry curvature

Then, you can proceed for the calculation of the Chern number of Berry curvature using a post-processing code 'calB.c'. The compilation of the code can be done in the director 'source' as

    % make calB
After the compilation is successfuly, you obtain the executable file 'calB'. Then, please copy it to the directory 'work', and execute it as follows:
    % ./calB graphene.scfout
    % ./calB graphene.scfout < calB.in > calB.out
    % mpirun -np 4 ./calB graphene.scfout < calB.in > calB.out

Parameters for calB

The input file 'calB.in' needs to be prepared as follows:

   0 0 1
   100 100
In the following we explain parameters for the calculation.

Output files

After the calculation by 'calB', the following files are generated.

Figure 74:
Berry curvature of graphene bands.