code: def kunc_v_single(p, v0, k0, k0p, order=5, min_strain=0.01):
      
      if p <= 1.e-5:
          return v0
  
      def f_diff(v, v0, k0, k0p, p, order=order):
          return kunc_p(v, v0, k0, k0p, order=order) - p
      v = brenth(f_diff, v0, v0 * min_strain, args=(v0, k0, k0p, p, order))
      return v
docs: find volume at given pressure using brenth in scipy.optimize
  
      :param p: pressure in GPa
      :param v0: unit-cell volume in A^3 at 1 bar
      :param k0: bulk modulus at reference conditions
      :param k0p: pressure derivative of bulk modulus at reference conditions
      :param order: order of Kunc function
      :param min_strain: defining minimum v/v0 value to search volume for
      :return: unit-cell volume at high pressure in GPa