Accurately computing the excitation energies is still a great challenge for density functional theory (DFT). Here we present our reparametrized functionals that showed improvement for such calculations especially the Rydberg states. Several well-known exchange and correlation functionals are selected as the starting point along with the Coulomb-attenuating method (CAM) for the long-range correction. Then the parameters especially those three for CAM are optimized in order to fit with the available experimental database. The fitting is mainly based on two criterions. (1) The difference between the vertical ionization potentials of some small molecules (H<sub>2</sub>O, N<sub>2</sub>, and CO etc.) measured experimentally and the negative of the corresponding computed Kohn-Sham eigenvalues of the occupied orbitals (excpet the core) are smaller than a threshold value. (2) The average absolute error of the excitation energies (mostly Rydberg transitions) of several selected organic molecules (ethylene, formaldehyde, and acetone etc.) computed by the time-dependent density functional theory (TDDFT) compared with the experiments is as small as possible. Several other properties are also included in the fitting procedure. The examples presented here demonstrate that the functionals with our optimized parameters could reproduce the excitation energies more accurately than most of the current DFT methods and are closer to the high level ab initio calculations like EOM-CCSD. The ground state properties computed with the new functionals also agree well with the experiments.

Increasing the accuracy of excited states calculations with optimized density functional theory

251st National Meeting (2016)

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