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

def altshuler_grun(v, v0, gamma0, gamma_inf, beta):
    """
    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
    """
    x = v / v0
    return gamma_inf + (gamma0 - gamma_inf) * np.power(x, beta)