def full_angles_to_k_approx(kinetic_energy, phi, psi, alpha, beta, theta,
    chi, inner_potential):
    """
    Small angle approximation of the momentum conversion functions. Depending on the value of alpha,
    which we do not small angle approximate, this takes a few different forms.

    :param kinetic_energy:
    :param phi:
    :param psi:
    :param alpha:
    :param beta:
    :param theta:
    :param chi:
    :param inner_potential:
    :return:
    """
    raise NotImplementedError()
