Figure 2: (a) Contour plot in the CuO plane of the displacement-induced charge density redistribution for the mode within the rigid ion model (RIM) for . (b) Same as (a), but for the nonlocal part of the charge response in the optimally doped state due to nonlocal EPI effects in the half-breathing mode . The displaced ions are indicated by a dot with an arrow. Full lines (—) mean that electrons are accumulated in the corresponding region of space and the broken dotted lines () indicate regions where the electrons are pushed away. is given in units of .