text: from ase.units import Hartree
  
  # Links 
  # http://cccbdb.nist.gov/introx.asp
  
  def bonding_energy(elements,system,input_unit='Hartree'):
          eb = 0
          for e in elements:
                  eb = eb + e
          eb = eb - system
          # units conversion from Hartree to eV 
          if input_unit == 'Hartree':
                  eb = eb *Hartree
          return eb
  
  # SYSTEM   IT          TRACE              EDFT                  EKIN+ENONLOC          CHARGE             EDFT+SIC          LOWEST
  # Si	   25       -175.876332706       -289.224747603        288.352899978         13.999999999       -289.097783990       -289.097783155
  # H	    4         -0.499658860         -0.499359706          0.499680555          0.999999999         -0.499921851         -0.499921856
  # Si2H6	    3       -355.252726935       -582.269513361        580.695534111         34.000000830       -582.054252014       -582.054252301
  	
  atom1 = -289.097783990 
  atom2 = -0.499921851 
  mol = -582.054252014 
  
  elements = [atom1,atom1,atom2,atom2,atom2,atom2,atom2,atom2]
  system = mol
  eb = bonding_energy(elements,system)
  print 'E_{B,PBE} = '+str(eb)+' eV'
  e_ref = 22.05206
  print 'E_{B,CCCBDB} = '+str(e_ref)+' eV'
  
  