Influence of the Delocalization Error and Applicability of Optimal Functional Tuning in Density Functional Calculations of Nonlinear Optical Properties of Organic Donor–Acceptor Chromophores

Abstract

Nonempirically tuned hybrid density functionals with range-separated exchange are applied to calculations of the first hyperpolarizability (β//) and charge-transfer (CT) excitations of linear "push-pull" donor-acceptor-substituted organic molecules with extended π-conjugated bridges. An unphysical delocalization with increasing chain length in density functional calculations can be reduced significantly by enforcing an asymptotically correct exchange-correlation potential adjusted to give frontier orbital energies representing ionization potentials. The delocalization error for a number of donor-acceptor systems is quantified by calculations with fractional electron numbers and from orbital localizations. Optimally tuned hybrid variants of the PBE functional incorporating range-separated exchange can produce similar magnitudes for β// as Møller-Plesset second-order perturbation (MP2) correlated calculations. Improvements are also found for CT excitation energies, with results similar to an approximate coupled-cluster model (CC2).

Ionization Energies, Electron Affinities, and Polarization Energies of Organic Molecular Crystals: Quantitative Estimations from a Polarizable Continuum Model (PCM)-Tuned Range-Separated Density Functional Approach

“…This gap-tuning procedure has been demonstrated to yield a good agreement between negative HOMO/LUMO energies and IEs/EAs as follows 37 :…”

“…While all these molecules have been studied before using optimal tuning methods in the gas phase, 37,48,70 we report here the results obtained from the PCM-tuning of their respective organic crystals. The basic idea is to employ the PCM model using the magnitudeequivalent dielectric constant (ε) of the crystal to simulate the crystal environment during the IPtuning process.…”

Enforcing the linear behavior of the total energy with hybrid functionals: Implications for charge transfer, interaction energies, and the random-phase approximation

“…The basic idea is to parametrize the exact-exchange energy such that the linearity condition is restored [19][20][21][22][23]. This route has been predominantly followed with the long-range separated BaerNeuhauser-Livshiz (BNL) hybrid functional [24,25].…”

Range-Separation Parameter in Tuned Exchange–Correlation Functionals: Successive Ionizations and the Fukui Function

“…The value of µ can be fixed or it can be 'tuned' on a system-by-system basis by minimising some tuning norm. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Whether the parameter is fixed or tuned, it is well established that such functionals yield improvements in many long-range properties, most notably charge-transfer excitation energies, and they have become the functional of choice in many studies.…”