Si-atoms substitutions effects on the electronic and optical properties of coronene and ovalene

Abstract

We report a computational comparative study of the ground and excited states properties of graphene nanoribbons, analyzing the case of coronene (C 24 H 12 ) and ovalene (C 32 H 14 ) and their silicon-atoms substituted counterparts with single, double and triple atomic insertions. We used density functional theory (DFT) and time-dependent DFT to quantify the effects on the electronic and optical properties as a result of the chemical modifications. In particular, we compared ground-state total energies, electron affinities, ionization energies, fundamental gaps and optical absorption spectra, between the original systems and each substituted one. For both the molecules, we observed a general reduction of the fundamental gap after chemical modification. Concerning the optical properties, therefore, we observed a redshift of the optical onset in all the cases; in particular, we have found that, in one ovalene and coronene trimer-substituted configuration, the absorption edge takes place in the IR.

First-Principles Investigation of the Optical Properties of Eumelanin Protomolecules

“…We checked the basis set convergence by adopting the Aug-cc-pVTZ (augmented, polarized triple-ζ) basis set, but it turned out that the Aug-cc-pVDZ basis already provides a very good agreement with experiments. We would like to point out that, in previous calculations on other molecular systems carried by some of us, ,− it had been found that using the B3LYP XC functional , and the 6–31+G*basis set was sufficient to obtain relaxed structures in good agreement with the corresponding experimental data, in particular for the eumelanin related precursors (DHI) and protomolecules. ,, In contrast, we find here that for systems like the tetrameric molecules of eumelanin such a level of theory (in terms of XC functional and basis set) leads to rather unsatisfactory results.…”

Electronic and Optical Properties of Small Metal Fluoride Clusters

“…In fact, the ΔSCF technique enables us to calculate the fundamental gap for each cluster. From the ΔSCF method, one obtains the quasiparticle gap (or fundamental gap) by the expression , …”

“…With respect to the exchange-correlation (XC) potential, we chose the B3LYP one since with respect to other possibilities, e.g., the Perdew–Burke–Ernzerhof (PBE) functional, it reproduces better results for different clusters, e.g., for many PAH molecules, for both ground and excited states, as previously established. − …”

“…We perform all the DFT and time-dependent DFT (TDDFT) calculations using the Gaussian16 computational code, an all-electron Gaussian-based package . This code enables us to characterize different clusters with respect to ground-state and excited-state properties. , In particular, the ground-state and the electronic properties, e.g., fragmentation energies, electron affinities, ionization energies, and quasiparticle (QP) gaps, are obtained here through the DFT method for all the fluoride molecules analyzed. Second, the time-dependent counterpart of this scheme allows the calculation of the optical properties (optical onsets, exciton binding energies) and to work out the absorption spectra from the visible up to the UV range covering the middle ultraviolet (MUV [4.13–6.20 eV]) and part of the far ultraviolet (FUV [6.20–10.16 eV]) spectral range.…”

Optical properties of nanostructured antiviral and anticancer drugs

“…60,61 The chosen basis-set is composed by a valence double- ζ set including d polarization functions (indicated with the symbol “*”) and diffuse functions (“+”) for each atom other than H. The selected couple of XC potential and basis-set has been successfully tested for many different atomic systems, both organic and inorganic, with different sizes and degrees of complexity. 62–77 Moreover, in several works (which studied nanostructures similar to ours) 6,9,41,51,78 the B3LYP XC functional or the 6-31+G* basis-set have been used.…”