Assessment of time-dependent density functional schemes for computing the oscillator strengths of benzene, phenol, aniline, and fluorobenzene

Abstract

In present study the relevance of using the time-dependent density functional theory (DFT) within the adiabatic approximation for computing oscillator strengths (f) is assessed using different LDA, GGA, and hybrid exchange-correlation (XC) functionals. In particular, we focus on the lowest-energy valence excitations, dominating the UV/visible absorption spectra and originating from benzenelike HOMO(pi)-->LUMO(pi(*)) transitions, of several aromatic molecules: benzene, phenol, aniline, and fluorobenzene. The TDDFT values are compared to both experimental results obtained from gas phase measurements and to results determined using several ab initio schemes: random phase approximation (RPA), configuration interaction single (CIS), and a series of linear response coupled-cluster calculations, CCS, CC2, and CCSD. In particular, the effect of the amount of Hartree-Fock (HF) exchange in the functional is highlighted, whereas a basis set investigation demonstrates the need of including diffuse functions. So, the hybrid XC functionals--and particularly BHandHLYP--provide f values in good agreement with the highly correlated CCSD scheme while these can be strongly underestimated using pure DFT functionals. These results also display systematic behaviors: (i) larger f and squares of the transition dipole moments (mid R:mumid R:(2)) are associated with larger excitation energies (DeltaE); (ii) these relationships present generally a linear character with R>0.9 in least-squares fit procedures; (iii) larger amounts of HF exchange in the XC functional lead to larger f, R:mumid R:(2), as well as DeltaE values; (iv) these increases in f, mid R:mumid R:(2), and DeltaE are related to increased HOMO-LUMO character; and (v) these relationships are, however, not universal since the linear regression parameters (the slopes and the intercepts at the origin) depend on the system under investigation as well as on the nature of the excited state.

Quantum Chemical Description of Absorption Properties and Excited‐State Processes in Photosynthetic Systems

“…There are only a few studies that assess the reliability of theoretical oscillator strengths, for example, that of ref. [76]. In that study, it was found that the oscillator strengths from TDDFT depend strongly on the choice of the XC functional.…”

Enhanced Two‐Photon Absorption of Organic Chromophores: Theoretical and Experimental Assessments

“…[89,94] Adiabatic time-dependent density functional theory (TD-DFT) [170,171] in the Kohn-Sham (KS) form is currently the method of choice for calculating the excited-state structure of large molecular systems. [172][173][174][175][176][177][178] Recently TD-DFT extensions for the calculations of molecular nonlinear optical properties have been suggested based on the residues of the quadratic response functions for TPA, [179,180] and on the quasi-particle formalism of the TD-KS equations for arbitrary frequency-dependent nonlinear optical polarizabilities. [181,182] Subsequently, the former approach was used for detailed studies of nonlinear polarizabilities in small organic molecules [183][184][185][186][187][188][189][190][191] and the latter method was applied to calculate OPA and TPA responses of several families of donor/acceptor sub-stituted conjugated organic chromophores [192][193][194][195][196][197] and various substituted branched structures.…”

Comparison of some representative density functional theory and wave function theory methods for the studies of amino acids

“…28 In studies of lowest energy valence excitations of several aromatic molecules using time-dependent DFT, BHandHLYP functional was found to provide oscillator strengths values in good agreement with highly correlated CCSD data or reported high-quality experimental results. 34 Some tests even claimed that BHandHLYP was the only hybrid DFT method that successfully described the potential energy surface obtained with the CCSD(T) calculation 35 and gave reliable excitation energies for the p-p charge-transfer complexes. 29 The question regarding the best DFT method for amino acids and related systems remains unanswered as the amino acid systems are characteristically different from the systems tested before.…”