Correlation and Charge Transfer in TDDFT

The charge transfer problem of time-dependent density functional theory (TDDFT) is well known. TDDFT also has a problem for extended π-systems even if there is no net charge transfer. Is there a connection? Yes, correlation!

In a recent communication in J. Chem. Phys., Exciton analysis in time-dependent density functional theory: How functionals shape excited-state characters,  we discuss the relation between static and dynamic charge transfer effects and their description in TDDFT. It is shown that both kinds of charge transfer are detrimental to local functionals while the problems can be remedied through Hartree-Fock exchange. The results are interpreted in terms of excitonic correlation. Only the inclusion of Hartree-Fock exchange leads to bound excitons while effective electron-hole repulsion is obtained for local functionals.