title: Spurious fractional charge on dissociated atoms: pervasive and resilient self-interaction error of common density functionals.
abstract: Semilocal density functional approximations for the exchange-correlation energy can improperly dissociate a neutral molecule XY (Y not =X) to fractionally charged fragments X(+q)...Y(-q) with an energy significantly lower than X0...Y0. For example, NaCl can dissociate to Na(+0.4)...Cl(-0.4). Generally, q is positive when the lowest-unoccupied orbital energy of atom Y0 lies below the highest-occupied orbital energy of atom X0. The first 24 open sp-shell atoms of the Periodic Table can form 276 distinct unlike pairs XY, and in the local spin density approximation 174 of these display fractional-charge dissociation. Finding these lowest-energy solutions with standard quantum chemistry codes, however, requires special care. Self-interaction-corrected (SIC) semilocal approximations are exact for one-electron systems and also reduce the spurious fractional charge q. The original SIC of Perdew and Zunger typically reduces q to 0. A scaled-down SIC with better equilibrium properties sometimes fails to reduce q all the way to 0. The desideratum of "many-electron self-interaction freedom" is introduced as a generalization of the one-electron concept.
authors.affiliation: Department of Physics, Tulane University, New Orleans, Louisiana 70118, USA.
authors.forename: Adrienn
authors.initials: A
authors.lastname: Ruzsinszky
authors.forename: John P
authors.initials: JP
authors.lastname: Perdew
authors.forename: Gábor I
authors.initials: GI
authors.lastname: Csonka
authors.forename: Oleg A
authors.initials: OA
authors.lastname: Vydrov
authors.forename: Gustavo E
authors.initials: GE
authors.lastname: Scuseria