Georgia M. A. Junqueira

Structural and vibrational study of graphene oxide via coronene based models: theoretical and experimental results

We use the Coronene (C24H12), a simple and finite molecule, to make a model to study the spectroscopic and structural alterations generated by oxygenated groups in graphene oxide (GO). Based on the Lerf–Klinowski model, we chose the hydroxyl [OH−], the carboxyl [COOH−] and the epoxy [the ring C2O inside the molecule] as our radicals of interest and study their collective and isolated effects. We perform geometry optimization, vibrational IR (via AM1 and DFT-B3LYP) and Raman spectra (via DFT-B3LYP) of a series of functionalized coronene molecules. As results, we obtain some useful data for the analysis of IR and Raman spectra of GO, which facilitate the understanding and identification of the peaks found in the experiment. Finally, we suggest a new model to study GO, producing an accurate signature when compared to our experimental data. Such molecule shows in more details of the structural effects caused by functionalization when compared to experimental data.

Theoretical study of the solvent effect on the aromaticity of benzene: a NICS analysis

AbstractNucleus-independent chemical shift (NICS) quantities for benzene–benzene and benzene–water species were obtained and are discussed in gas phase and in solution. Besides standard polarizable continuum model (PCM) calculations, sequential Monte Carlo/quantum mechanics (S-MC/QM) were also performed. Benzene was shown to be slightly more aromatic in condensate phase when we considered the average solvent configuration (ASEC) approach with explicit molecules. FigureNICS quantities versus benzene clusters

Estudo teórico de propriedades ópticas não-lineares de nanotubos de carbono de parede única quimicamente modificados

Structure and first hyperpolarizability for a series of armchair a(5,5) chemically modified carbon nanotubes (CNT) were calculated at semiempirical and density functional levels of theory. The 4,4´-substituted stilbenes were selected as chromophore with substituents at position 4´ set to X=NO2, H, Cl, OH and NH2. The calculated values for static first hyperpolarizability (β) were almost linearly dependent on the electronic effect of the group X, increasing from NO2 to NH2. At DFT level the effect of inserting the chromophore in the CNT surface was to enhance the β value up to 70% relative to the free 4,4´-substituted stilbene.

Enhancement of Nonlinear Optical Properties of Graphene Oxide-based Structures: Push-Pull Models

Through DFT calculations and the finite field approach, it is possible to identify some structural and electronic aspects that could lead to enhancement of the nonlinear optical (NLO) molecular properties of graphene oxide and its derivatives. We proposed a molecular design scheme of NLO response based on push–pull structures. The best NLO models contain –COOH at their edges, acting as electron acceptors, and –OH in the basal plane, acting as an electron donor.

Theoretical study of nonlinear optical properties of cobalt bis (dicarbollide) derivatives: the effect of substituents

In the present work, molecular first-order hyperpolarizability (

Gaussian basis sets for ab initio calculation of NLO properties of polyatomic molecules

\beta _{\mathrm{tot}}

Exploring the effect of substitutional doping on the electronic properties of graphene oxide

βtot) and dipole moment (d) are obtained at B3LYP/6–31G(d,p) level of theory by coupled perturbed Hartree–Fock method within the static approach. The investigated molecules are a series of substituted cobalt bis (dicarbollide) derivatives: Hydrogens bonded to the two carbon atoms are replaced by acceptor and donor electron substituents. Correlations between the Hammett electronic parameters of the substituents and the molecular properties are tested. Among them, the named push–pull compounds produced the largest calculated values of