0 2 4 6 8 r$_{s}$ 20 40 60 80 100 120 140 g (0) This work This work (No extra) Arponen & Pajanne [10] Boronski & Nieminen [6] Lantto [11] Stachowiak & Lach [18] Apaja  et al.  [19] Ortiz [13] Fraser [14] FIG. 3: (Color online) Electron-positron contact PCF g (0) against density parameter r s . The results were obtained by averaging the g (0) values obtained in cells with N = 114, 162, and 246 electrons for 1 ≤ r s ≤ 7 and N = 114 and 162 at r s = 8. Various contact PCF results from the literature are also shown. completeness by fitting our data to the empirically determined expression g$_{E}$ cut (0) = g ∞ (0)+ $_{a/}$√$_{E}$$_{cut}$$_{+}$$_{b/E}$$_{cut}$$_{, where}$ a and b are fitting parameters. The residual finite-size error in g (0) is less than about 1%. The electron-positron contact PCF is plotted in Fig. 3. Adapting the fitting form of Ref. [6] slightly, we represent our contact PCF data by where a$_{3}$$_{/}$$_{2}$ = − 1 . 56672, a$_{2}$ = 4 . 16983, a$_{7}$$_{/}$$_{3}$ = − 3 . 579, and a$_{8}$$_{/}$$_{3}$ = 0 . 836389. Equation (4) satisfies both the high- density (random phase approximation) [12] and low-density (Ps $^{−}$) limiting behavior [11]. The extra interaction reduces the contact PCF at all the densities we have studied, by about 8% at r$_{s}$ = 1, rising to about 15% at r$_{s}$ = 8. Our electron-positron PCF results are in reasonably good agreement with the many-body-theory results of [13, 14, 21, 22], but are in strong disagreement with the QMC results [16, 17], which give much smaller g (0) = 1 + 1 . 23 r$_{s}$ + a$_{3}$$_{/}$$_{2}$r 3 / 2 s + a$_{2}$r 2 s + a$_{7}$$_{/}$$_{3}$r 7 / 3 s + a$_{8}$$_{/}$$_{3}$r 8 / 3 s + 0 . 173694 r 3 $_{s}$, (4) 7