- #1

[tex]G(\mathbf{k}) = \frac{1}{2} \int d^{3N}\mathbf{R}_1 d^{3N}\mathbf{R}_2 e^{\imath \mathbf{k}\cdot(\mathbf{R}_1 - \mathbf{R}_2)} n_2(\mathbf{R}_1, \mathbf{R}_2) [/tex]

My guess is that it is some sort of momentum distribution, but that's only a guess.