def get_LDA_energy(exct, vxct, s):
    """Evaluating the energy of LDA functional in a batch of spherical projection directions.

    Parameters
    ----------
    exct: np.ndarray
        The exchange-corelation energy of original LDA function.
        
    vxct: tuple of (vrho, vs), where vrho and vs are np.ndarray with shape (Ngrid)
        The exchange-corelation energy of original LDA function.
        
    s: np.ndarray
        The spin density (Ngrid)

    Returns:
    ----------
    exc = exct + vxct[1]*s : np.ndarray with the shape (Ngrid)
        The exchange-corelation energy of a single direction of the multi-collinear approach.
    """
    return exct + vxct[1]*s