Origin of the field-counteracting term of the Kohn-Sham exchange-correlation potential of molecular chains in an electric field - art. no. 012507

The origin and the mechanisms responsible for an ultranonlocal field-counte racting term in the Kohn-Sham exchange-correlation potential nu(xc) of mole cular chains in an external electric held are established for prototype sys tems. Using various analysis tools-conditional probability amplitude analys is, construction of the (nearly) exact v(xc), one-electron perturbation the ory, and Krieger-Li-Iafrate (KLI) calculations-it is shown that a field-cou nteracting term emerges in the "response'' part v(resp) of nu(sc). For syst ems A(2) of two open-shell units A, with H-2 as a prototype, the left-right electron Coulomb correlation generates a step in nu(resp), which effective ly compensates for an electric field in the limit of large interatomic dist ances. For systems A(n) of closed shell units A, with He-2 and H-2 + H-2 as prototypes, a held-counteracting term is generated in nu(resp) by the Paul i repulsion of electrons in the occupied Kohn-Sham orbitals. An analytical estimate of the field-counteracting step is obtained for He-2 with the exch ange-only KLI model of nu(resp), and the existence of an ultranonlocal line ar term in nu(resp) is established with KLI calculations on the prototype m olecular chain H-18.