Json-serializable dict representation of COHP.

def as_dict(self):
        """
        Json-serializable dict representation of COHP.
        """
        d = {"@module": self.__class__.__module__,
             "@class": self.__class__.__name__,
             "are_coops": self.are_coops,
             "efermi": self.efermi,
             "energies": self.energies.tolist(),
             "COHP": {str(spin): pops.tolist()
                      for spin, pops in self.cohp.items()}}
        if self.icohp:
            d["ICOHP"] = {str(spin): pops.tolist()
                          for spin, pops in self.icohp.items()}
        return d