code: def _R2deriv(self,R,phi=0.,t=0.):
          
          return self._Pot.R2deriv(R,0.,phi=phi,t=t,use_physical=False)
docs: NAME:
             _R2deriv
          PURPOSE:
             evaluate the second radial derivative
          INPUT:
             R
             phi
             t
          OUTPUT:
             d2phi/dR2
          HISTORY:
             2016-06-02 - Written - Bovy (UofT)