def METHOD_NAME(T, debye_T, n):
    """
    Heat capacity at constant volume.  In J/K/mol
    """
    if T <= eps:
        return 0.0
    x = debye_T / T
    C_v = (
        3.0
        * n
        * constants.gas_constant
        * (4.0 * debye_fn_cheb(x) - 3.0 * x / (np.exp(x) - 1.0))
    )
    return C_v