Second virial coefficient (SVC) of the Lennard-Jones potential.

The LJ potential describes both the attraction and repulsion between non-bonded beads. SVC is used to determine the value of ϵ for which repulsive and attractive bead-bead interactions are equal (theta solvent condition). The integral for B(T) cannot be calculated analytically, but an accurate approximation can be derived from the expansion [88]. In the figure, the function B(T) is plotted as a function of ϵ/ k_BT for k = 1 to 10. For larger values of k, the graph saturates, and at B = 0, we get ϵ_θ = 0.2925 k_BT.

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