Towards a limited XANES refinement in strongly correlated systems

Three components of O1 atom displacements have been derived from the direct fit of the polarized E//ab Cu K-edge XANES spectrum of Nd1.85Ce0.15CuO4-de lta superconductor. The best fit is achieved for a 60 to 40% mixture of 2x2 undistorted antiferromagnetic and modified charge density wave (MCDW) doma ins. The local structure of the MSDW is characterized by correlated displac ements of Delta O1(parallel to)=0.12+/-0.04, Delta O1(perpendicular to)=0. 25+/-0.08, and Delta O1(z)=0.12+/-0.1 Angstrom. An agreement factor over th e range of 8980-9040 eV is 2-3 times smaller than it may be obtained from s ingle-electron MS calculations. This improvement comes from accounting for many-body excitations and the relationship between electronic and local str ucture in the CuO2 planes.