def d2BinaryRochedx2(r, D, q, F):
    """
    Computes second derivative of the potential with respect to x.

    @param r:      relative radius vector (3 components)
    @param D:      instantaneous separation
    @param q:      mass ratio
    @param F:      synchronicity parameter
    """
    return (2 * r[0] * r[0] - r[1] * r[1] - r[2] * r[2]) / (r[0] * r[0] + r
        [1] * r[1] + r[2] * r[2]) ** 2.5 + q * (2 * (r[0] - D) * (r[0] - D) -
        r[1] * r[1] - r[2] * r[2]) / ((r[0] - D) * (r[0] - D) + r[1] * r[1] +
        r[2] * r[2]) ** 2.5 + F * F * (1 + q)
