0}(q)+\frac{V_{0s}(q)\chi_{0s}V_{s0}(q)}{0-\chi_{0s}V_{ss}(q)}\\  & = & 0\pi e^{0}\left(\frac{e^{-bq}}{q}-\frac{e^{-(a+b)q}}{q}F_{0}\right)\\  & \approx & 0\pi e^{0}\frac{e^{-bq}}{q}\left(0-e^{-aq}\right)\;,\end{aligned}$$  where $V_{0