CORRELATION IN DOUBLE-LAYER 2-DIMENSIONAL ELECTRON-GAS SYSTEMS - SINGWI-TOSI-LAND-SJOLANDER THEORY AT B=0

We investigate the interaction effects for double-layer two-dimensional electron-gas systems in the absence of a magnetic field using both the random phase approximation (RPA) and Singwi-Tosi-Land-Sjolander (STLS) approximations. We show that the RPA overestimates correlation effects and that one needs, at a minimum, to include local-field corrections in order to get reliable estimates for the correlation energy and pair-distribution functions. The electron momentum distribution in double-layer systems is also studied by evaluating the electron self-energy from the screened exchange interaction. We find that RPA and STLS dielectric functions give quantitatively similar results for this quantity. The momentum distribution function depends very weakly on the layer separation of double-layer systems.