code: def d2BinaryRochedx2(r, D, q, F):
      
      return (2*r[0]*r[0]-r[1]*r[1]-r[2]*r[2])/(r[0]*r[0]+r[1]*r[1]+r[2]*r[2])**2.5 +\
            q*(2*(r[0]-D)*(r[0]-D)-r[1]*r[1]-r[2]*r[2])/((r[0]-D)*(r[0]-D)+r[1]*r[1]+r[2]*r[2])**2.5 +\
            F*F*(1+q)
docs: Computes second derivative of the potential with respect to x.
  
      @param r:      relative radius vector (3 components)
      @param D:      instantaneous separation
      @param q:      mass ratio
      @param F:      synchronicity parameter