Electric field dependence of the exchange-correlation potential in molecular chains

Density functional calculations on the (non)linear optical properties of co njugated molecular chains using currently popular exchange-correlation (xc) potentials give overestimations of several orders of magnitude. By analyzi ng "exact" and Krieger-Li-Iafrate re potentials, the error is traced back t o an incorrect electric field dependence of the "response part" of the re p otential in local and gradient-corrected density approximations, which lack a linear term counteracting the applied electric field.