Neutral-ionic interface in charge-transfer salts with long-range coulomb interactions

Abstract

Coulomb interactions - Vα stabilize both neutral and ionic lattices against charge-transfer (CT) excitations for Madelung-constant α>1. The neutral-ionic phase boundary δ c(χ) and ionicity jump Δ q(χ) are accurately given by the lowest-order corrections in χ = ¦ t¦/ V(α-1) for χ ⩽ 0.2 and Mulliken CT integral t. Numerical solutions of (2 N ⩽ 18)-site DA rings, with D 2+ and A 2− excluded, show Δ q(χ) to vanish for χ > χ c = 0.33±0.02, where δ c/¦ t¦=0.39±0.02, in contrast to δ c = 0 in two-state models that neglect the D + and A − spins.