code: def _phi2deriv(self,R,z,phi=0.,t=0.): #pragma: no cover
          
          raise AttributeError
          # Implementation above does not work bc SCF.phi2deriv is not implemented
          return self._scf.phi2deriv(R,z,phi=phi,use_physical=False)
docs: NAME:
             _phi2deriv
          PURPOSE:
             evaluate the second azimuthal derivative for this potential
          INPUT:
             R - Galactocentric cylindrical radius
             z - vertical height
             phi - azimuth
             t - time
          OUTPUT:
             the second azimuthal derivative
          HISTORY:
             2016-12-26 - Written - Bovy (UofT/CCA)