Eur. Phys. J. B (2018) 91: 122
https://doi.org/10.1140/epjb/e2018-90088-6

Regular Article

Bond-breaking excitations with diverging coupling matrix of response density functional theory from highest-level functionals^★

¹ Computational Molecular Science Research Team, RIKEN Advanced Institute for Computational Science, Kobe, Japan
² Section Theoretical Chemistry, VU University, Amsterdam, The Netherlands

^a e-mail: o.gritsenko@vu.nl

Received: 22 February 2018
Received in final form: 13 April 2018
Published online: 18 June 2018

Abstract

Bond-breaking excitations ω_α are the problematic case of adiabatic time-dependent density functional theory (TDDFT). The calculated ω_α erroneously vanishes with the bond elongation, since the Hartree-exchange-correlation kernel and the corresponding response coupling matrix K of standard approximations lack the characteristic divergence in the dissociation limit. In this paper an approximation for K is proposed constructed from the highest-level functionals, in which both occupied and virtual Kohn-Sham orbitals participate with the weights w_p. The latter provide the correct divergence of K in the limit of dissociating two-electron bond. The present K brings a decisive contribution to the energy of the ¹Σ_u⁺ in the prototype H₂ molecule calculated for various H-H separations. At shorter separations it improves ω_α compared to the zero-order TDDFT estimate, while at the largest separation it reproduces near-saturation of the reference excitation energy.