Abstract
In calculations based on density functional theory, the "HOMO-LUMO gap"(difference between the highest occupied and lowest unoccupied molecular orbital energies) is often used as a low-cost, ad hoc approximation for the lowest excitation energy. Here we show that a simple correction based on rigorous ensemble density functional theory makes the HOMO-LUMO gap exact in principle and significantly more accurate in practice. The introduced perturbative ensemble density functional theory approach predicts different and useful values for singlet-singlet and singlet-triplet excitations, using semilocal and hybrid approximations. Excitation energies are similar in quality to time-dependent density functional theory, especially at high fractions of exact exchange. The approach therefore offers an easy-to-implement and low-cost route to robust prediction of molecular excitation energies.
Original language | English |
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Pages (from-to) | 2452-2458 |
Number of pages | 7 |
Journal | Journal of Physical Chemistry Letters |
Volume | 13 |
Issue number | 10 |
DOIs | |
State | Published - 17 Mar 2022 |
All Science Journal Classification (ASJC) codes
- General Materials Science
- Physical and Theoretical Chemistry