The electrical response of molecular chains is dramatically overestimated by local and semilocal density functionals. We show that Kohn-Sham density-functional theory yields accurate linear and nonlinear polarizabilities when the exact exchange energy is employed together with the corresponding exact Kohn-Sham potential $v_{\mathrm{x}}(\mathbf{r})$. We further show that approximations to $v_{\mathrm{x}}(\mathbf{r})$ that are very accurate for the ground-state energy can nevertheless fail badly for the response because of potential barriers that have little effect on the ground-state energy but strongly affect the electron mobility.

• Received 4 August 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.213002