code: def altshuler_grun(v, v0, gamma0, gamma_inf, beta):
      
      x = v / v0
      return gamma_inf + (gamma0 - gamma_inf) * np.power(x, beta)
docs: calculate Gruneisen parameter for Altshuler equation
  
      :param v: unit-cell volume in A^3
      :param v0: unit-cell volume in A^3 at 1 bar
      :param gamma0: Gruneisen parameter at 1 bar
      :param gamma_inf: Gruneisen parameter at infinite pressure
      :param beta: volume dependence of Gruneisen parameter
      :return: Gruneisen parameter