Electronic responses of long chains to electrostatic fields: Hartree-Fock vs. density-functional theory: a model study

How well do self-interaction corrections repair the overestimation of static polarizabilities in density functional calculations?

We examine the effect of removing self-interaction error (SIE) on the calculation of molecular polarizabilities in the local spin density (LSDA) and generalized gradient approximations (GGA). To this end, we utilize a database of 132 molecules taken from a recent benchmark study [Hait and Head-Gordon, Phys. Chem. Chem. Phys., 2018, 20, 19800] to assess the influence of SIE on polarizabilities by comparing results with accurate reference data. Our results confirm that the general overestimation of molecular polarizabilities by these density functional approximations can be attributed to SIE. However, removing SIE using the Perdew-Zunger self-interaction-correction (PZ-SIC) method, implemented using the Fermi-Löwdin Orbital SIC approach, leads to an underestimation of molecular polarizabilities, showing that PZ-SIC overcorrects when combined with LSDA or GGA. Application of a recently proposed locally scaled SIC [Zope, et al., J. Chem. Phys., 2019, 151, 214108] is found to provide more accurate polarizabilities. We attribute this to the ability of the local scaling scheme to selectively correct for SIE in the regions of space where the correction is needed most.

Molecular and NLO Properties of Red Fluorescent Coumarins - DFT Computations Using Long-Range Separated and Conventional Functionals

Comparative study of nonlinear optical properties of red fluorescent coumarins was carried out with density functional theory based ab initio method using the popular global hybrid (GH) and range separated hybrid (RSH) functionals and correlated with the spectroscopic values. The GHs - M06 L, PBE1PBE, M06, BHHLYP, M062X and M06HF and RSHs - HISSbPBE, wB97, wB97X, HSEH1PBE, CAM-B3LYP and wB97XD in combination with the double zeta basis function 6-311 + G(d,p) were used. The computed polarizability (α₀), hyperpolarizability of the first order (β₀) and second order (γ) computed by the RSHs are closer to the spectroscopic values compared to GHs. Polarizabilities computed with the functionals BHHLYP and M06-2X are closer with the spectroscopic values. Incorporation of additional cyano group enhances the NLO response. An increase in electrophilic nature contributed from the reduced orbital band gap culminating an increase in α₀, β₀, and γ in all the cases. The NLO response was found to be highly solvent dependent that is the polarity of the micro environment created by the solvents. To understand the agreement and accuracy among the NLO parameters obtained from the selected DFT functionals and the spectroscopic values, the mean absolute error (MAE) and vibrational contribution parameters are presented. Two photon absorption (TPA) cross section depends upon the molecular structure where π-framework is an important factor rather than number of acceptors.