However, if the neutral condition ∑ ∑ i = 1 N n i = 0 holds, the second term is equal to − − 2 π π ∑ ∑ 1 ≤ ≤ i < j ≤ ≤ N n i n j ln ⁡ ⁡ ( | x j − − x i | / L ) , which is the total potential energy of a two-dimensional Coulomb gas. The scale L is an arbitrary scale that renders the argument of the logarithm dimensionless.