Weeks-Chandler-Andersen chains

The Weeks-Chandler-Andersen chain model consists of units composed of the Weeks-Chandler-Andersen reference system model, i.e. :

$\Phi _{\rm {repulsive}}(r)=\left\{{\begin{array}{ll}\Phi _{\rm {LJ}}(r)+\epsilon &{\rm {if}}\;r<2^{1/6}\sigma \\0&{\rm {if}}\;r\geq 2^{1/6}\sigma \end{array}}\right.$

where Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \Phi_{\rm LJ}(r)} represents the Lennard-Jones model.