Improving the Description of the Optical Properties of Carotenoids by Tuning the Long-Range Corrected Functionals

Abstract

In this work we use gap-fitting procedure to tune the long-range corrected functionals and accurately investigate the electronic and optical properties of the five main molecules composing Buriti oil (extracted from Mauritia flexuosa L.) in the framework of density functional theory (DFT) and time-dependent (TD) DFT. The characteristic length (1/ω) was observed to be entirely system dependent, though we concluded that its determination is of fundamental importance to rescue geometrical, electronic, and optical properties with accuracy. We demonstrate that our approach of tuning characteristic length for each system resulted in an absorbance spectra in better experimental agreement when compared to the traditional methodology. Therefore, this study indicates that the tuning of the range-separation parameter is crucial to improve the description of the optical properties of conjugated molecules when TDDFT is used. For example, the wavelength of maximum absorption, λmax, for the phytofluene, obtained using B3LYP, is 381 nm, while using the gap-fitting procedure for the tuned-LC-BLYP the estimated λmax changed to 358 nm. The latter estimate is in better agreement with the experimental value of 350 nm.

A Theoretical Study of the Chemical Reactivity of Neohesperidin Dihydrochalcone Through Conceptual DFT Descriptors

“…Indeed, the values of JI , JA and JGap are not exactly zero. However, their values can be favorably compared with the results presented for these quantities in the work of Lima et al [22], where the minima has been obtained by chosing a parameter that enforces that behavior.…”

“…Inspired from previous works on this subject [14,22], and with the object of analyzing our results in order to verify the fulfillment of the "Koopmans' theorem in DFT", we have designed several descriptors that relate the results obtained through the HOMO and LUMO calculations with those obtained by means of the vertical I and A with a ∆SCF procedure. However, it must be stressed that it is not our intention to perform a gapfitting by minimizing a descriptor by chosing optimal range-separation parameter γ, but to check if the density functionals considered in this study, in which, some of the contain a fixed range-separation parameter γ, obbey the "Koopmans' theorem in DFT".…”

“…As a matter fact, there is no range-separation parameter γ in our designed descriptors. Moreover, we have considered A as minus the energy of the LUMO of the neutral system instead of considering A as minus the energy of the HOMO of the N+1 electron system, as it was in the mentioned works [14,22].…”

“…This is a consequence of the better fullfilment of the Koopmans' theorem that leads to better agreement of the orbital energies with the I and A. For example, Lima et al [22] have re-cently presented an improved description of the optical properties of carotenoids by tuning some longrange corrected functionals.…”

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“…As a matter of fact, there is no range-separation parameter  in our designed descriptors. Moreover, we have considered A as minus the energy of the LUMO of the neutral system instead of considering A as minus the energy of the HOMO of the N+1 electron system, as it was in the mentioned works [48,49].…”