EXTENDED MOMENT FORMATION AND 2ND-NEIGHBOR COUPLING IN LI2CUO2

The Cu-O edge-sharing compound Li2CuO2, whose ferromagnetic chains are antialigned, is found from local spin density calculations to display several surprising characteristics: (1) the ordered moment per formul a unit of 0.92 mu(B) is the largest for any low dimensional cuprate sy stem, in agreement with experiment; (2) 40% of this moment lies on the neighboring O ions, making it equal to the largest oxygen moment yet calculated; and (3) the second neighbor couplings are larger than near est neighbor couplings. All of these phenomena arise naturally due to an energetically isolated effective d(yz)-type orbital that includes v ery strong O p(sigma) character. [S0031-9007(98)07142-7].