plot Band Structure
===========

The bash script extracts data of band structure from OUTCAR file, and write the output file band.dat
The python script use the band.dat to plot band structure with the output file band.jpg


band.sh
::
      #edit by lipai@mail.ustc.edu.cn
      #get num of band
      num=`grep NBANDS OUTCAR |awk '{print $NF}'`
      E_fermi=`grep E-fermi OUTCAR | awk '{print $3}'`
      grep "band No." OUTCAR -A $num >temp
      echo "" >>temp
      split -l 26 -d temp bands
      for i in bands*; do sed -i '$d' $i;awk -v num=$i 'BEGIN{printf("%s\t",num)};{if(NR>1) printf("%f\t",$2)};END{printf("\n")}' $i >>band.dat; done
      sed -i s/bands// band.dat
      rm bands* temp
      python plot_band band.dat $num $E_fermi

plot_band.py
::

      import sys
      import matplotlib as mpl
      import matplotlib.pyplot as plt
      import numpy as np

      mpl.rcParams['agg.path.chunksize']=10000

      arg_num=len(sys.argv)

      if arg_num!=5:
          print("wrong inputs!!!\n")
          print("format:")
          print("plot_band filename band_num E_fermi")
          exit()

      filename=sys.argv[1]
      band_num=int(sys.argv[2])
      E_fermi=float(sys.argv[3])
      split=int(sys.argv[4])

      data=np.loadtxt(filename)

      #plt.figure(figsize=(10,10))


      for i in range(1,band_num+1):
          #plt.plot(data[:,0],data[:,i],'.b')
          plt.plot(data[:,0],data[:,i]-E_fermi,'-g',linewidth=3,alpha=0.4)

      min=10
      max=-10
      for (x,y),val in np.ndenumerate(data):
          val=val-E_fermi
          if val>0 and val<min:
              min=val
              minx=x
              miny=y
          elif val<0 and val>max:
              max=val
              maxx=x
              maxy=y
      plt.plot(minx,min,'or')
      plt.plot(maxx,max,'or')
      ax=plt.gca()
      ax.annotate(" "+str(minx)+"  "+str(min),xy=(minx+x/30,min),color='r',bbox=dict(boxstyle='round,pad=0.2', fc='w', alpha=0.7))
      ax.annotate(" "+str(maxx)+"  "+str(max),xy=(maxx+x/30,max),color='r',bbox=dict(boxstyle='round,pad=0.2', fc='w', alpha=0.7))
      if minx==maxx:
            text="Direct band gap with gap of "+str(min-max)+" eV"
      else:
            text="Indirect band gap with gap of "+str(min-max)+" eV"
      plt.title(text)
      plt.ylabel('Energy/eV')
      plt.ylim(-4,4)
      plt.xlim(data[0,0],data[-1,0])
      plt.axhline(0.0,label='E-fermi',color='r',alpha=0.2)
      for i in range(1,split):
            plt.axvline(i*data[-1,0]/split,color='k',alpha=0.2)
      #plt.savefig("band.jpg",dpi=300)
      plt.show()