\(F_{hydro}=-\left(\frac{dE_{hydro}}{dd}\right)=\frac{\left(-2\gamma\left(a-a_0\right)\exp\left(-\frac{d}{D_{hydro}}\right)\right)}{D_{hydro}}\)\(E_{hydro}=-2\gamma\left(a-a_0\right)\exp\left(-\frac{d}{D_{hydro}}\right)\)