It is now well-established that time-dependent density functional theory (TDDFT) vertical excitation energies determined using local exchange-correlation functionals break down completely when the degree of spatial overlap between the relevant occupied and unoccupied orbitals drops too low. In this talk, we highlight the far-reaching ...[+]

It is now well-established that time-dependent density functional theory (TDDFT) vertical excitation energies determined using local exchange-correlation functionals break down completely when the degree of spatial overlap between the relevant occupied and unoccupied orbitals drops too low. In this talk, we highlight the far-reaching implications of this observation for the calculation of excited state potential energy surfaces and show that it can also provide a useful perspective for understanding why simple chemical changes can lead to a significant reduction in TDDFT accuracy. The problems are essentially eliminated using a Coulomb-attenuated functional[-]