Square well lines potential
From SklogWiki
The square well lines (SWL) potential is given by
\[\Phi_{\mathrm{SWL}}(1,2) = \frac{\epsilon n^2}{L^2} \int_{-L/2}^{L/2}\int_{-L/2}^{L/2} \left[ H(s_2 - r(\lambda, \mu)) -H(s_1 -r(\lambda, \mu)) \right]~{\mathrm d}\mu~{\mathrm d}\lambda \]
where \(H()\) is the Heaviside step distribution.