Simplified tuning of long-range corrected time-dependent density functional theory

Range-separated hybrid functionals have dramatically improved the description of charge-transfer excitations in time-dependent density functional theory (TD-DFT), especially when the range-separation parameter is adjusted in order to satisfy the ionization energy (IE) criterion, eHOMO = –IE. However, this "optimal tuning" procedure is molecule-specific, inconvenient, expensive for large systems, and problematic in extended or periodic systems. Here, we consider an alternative procedure known as global density-dependent (GDD) tuning, which sets the range-separation parameter in an automated way based on properties of the exchange hole. In small molecules, we find that both IE- and GDD-tuned functionals afford remarkably similar TD-DFT excitation energies, for both valence and charge-transfer excitations. However, GDD tuning is more efficient and is well-behaved even for large systems, providing a black-box solution to the optimal-tuning problem that can replace IE tuning for many applications of TD-DFT.