We develop an extension of the sum-rule version of the Singwi, Tosi, Land,
and Sjolander (STLS) scheme applied to a double-layer electron system. We p
resent analytical expressions for the intralayer and interlayer static stru
cture factors and corresponding local-field corrections which agree quite w
ell with the full STLS calculations. Some applications of our basic results
and further generalizations of our method are discussed. (C) 1999 Academic
Press.