Assessment of range-separated functionals in the presence of implicit solvent: Computation of oxidation energy, reduction energy, and orbital energy

Abstract

Recently, we have investigated the ionization potential (IP) theorem for some small molecules in the presence of external electric field [M. P. Borpuzari et al., J. Chem. Phys. 144, 164113 (2016)]. In this article, we assess the performance of some density functionals, local density approximation, generalized-gradient approximation (GGA), hybrid, meta-GGA hybrid, and range-separated functionals in the presence of two different solvent dielectrics, water and cyclohexane, in reproducing the vertical oxidation energy, reduction energy, and the frontier orbital energies. We also study the accessibility of different computational solvent models like the polarizable continuum model (PCM) and non-equilibrium PCM (NEPCM) in reproducing the desired properties. In general, the range-separated functionals do not perform well in reproducing orbital energies in the PCM. Range separation with the NEPCM is better. It is found that CAM-B3LYP, M06-2X, and ωB97XD functionals reproduce highest occupied molecular orbital energy in solvents, which may be due to the cancellation of PCM and density functional theory errors. Finally, we have tested the validity of the IP theorem in the solvent environment.

Modeling absorption spectra of molecules in solution

“…A smaller range‐separation parameter is predicted for increasing system size when using IP tuning, for both increasing molecular size and increasing amount of QM solvent, whereas improved agreement with λ max values is obtained by increasing the value of the range‐separation parameter for molecules of increasing size . IP tuning has been employed with polarizable continuum models, resulting in an overly small value for the range‐separation parameter if using equilibrium solvation for both the neutral and cationic systems . More reasonable values for the range‐separation parameter are obtained for modeling ionization with a polarizable continuum model within the nonequilibrium TDDFT formulation …”

Do water's electrons care about electrolytes?

“…We note here that inclusion of the solvation effects in the ionization potential theorem is non-trivial. The embedding of the non-equilibrium response of the solvent to the Kohn–Sham orbital energies has been a subject of a debate, so far attempts were made mainly in different directions 97,98. The IEDC approach is fully consistent in this respect 83…”

Modeling Electronic Excited States of Molecules in Solution

“…106 IP tuning has been employed with polarizable continuum models, resulting in an overly small value for the range-separation parameter if using equilibrium solvation for both the neutral and cationic systems. [107][108][109][110] More reasonable values for the range-separation parameter are obtained for modeling ionization with a polarizable continuum model within the non-equilibrium TDDFT formulation. 111…”