Ruzsinszky Adrienn, Perdew John P, Csonka Gábor I, Vydrov Oleg A, Scuseria Gustavo E
Department of Physics, Tulane University, New Orleans, Louisiana 70118, USA.
J Chem Phys. 2006 Nov 21;125(19):194112. doi: 10.1063/1.2387954.
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.
用于交换关联能的半局域密度泛函近似可能会不恰当地将中性分子XY（Y≠X）离解为分数电荷碎片X(+q)…Y(-q)，其能量显著低于X0…Y0。例如，氯化钠可以离解为Na(+0.4)…Cl(-0.4)。一般来说，当原子Y0的最低未占据轨道能量低于原子X0的最高占据轨道能量时，q为正。元素周期表中的前24个开放sp壳层原子可以形成276种不同的不同对XY，在局域自旋密度近似中，其中174种显示出分数电荷离解。然而，使用标准量子化学代码找到这些最低能量解需要特别小心。自相互作用校正（SIC）半局域近似对于单电子系统是精确的，并且还会降低虚假的分数电荷q。Perdew和Zunger最初的SIC通常会将q降低到0。具有更好平衡性质的缩小版SIC有时无法将q一直降低到0。“多电子自相互作用自由度”的需求作为单电子概念的推广被引入。
