Performance of Hybrid DFT Compared to MP2 Methods in Calculating Nonlinear Optical Properties of Divinylpyrene Derivative Molecules.

A series of divinyl-pyrene derivatives of the form D-vinyl-pyrene-vinyl-A, in which D corresponds to an electron donor group and A to an electron acceptor group, were studied in this work. The first purpose was to determine the optimal HF % exchange as incorporated in a range of hybrid functionals (M06HF, M062X, M06L, CAM-B3LYP, PBE0, BMK, and B3LYP) capable to produce, reliably and as close as possible to those obtained from MP2 calculations, NLO parameters and, in particular, first-order static hyperpolarizabilities. The CAM-B3LYP functional was revealed to be the most suitable one. The pair N(CH3)2/NO2 was then determined as the most efficient pair of groups in producing appreciable NLO responses. The effect of the substitution position on the pyrene moiety was also investigated, whereby aligning the two substituents involving the D and A groups in the direction of the dipole moment as in the (1,6 DVP) derivatives was shown to be most favorable for increasing the NLO parameters.

Relaxed energetic maps of kappa-carrabiose: a DFT study.

The B3LYP density function was used with the 6-31G(d) basis set to perform relaxed energetic contour maps of the charged form of kappa-carrabiose in the gas phase and for the neutral form first in the gas phase and then by simulating the presence of water as solvent using the Onsager model. Only one starting conformation has been considered to perform all the calculations. Rigid energetic maps have been then constructed either by addition of diffuse or polarization functions to the basis set obtaining in that way 6-31+G(d)//6-31G(d), 6-31+G(d,p)//6-31G(d), and 6-311++G(d,p)//6-31G(d) energetic maps that have been carefully examined. The obtained structures corresponding to the lower energy conformers have been then fully optimized using different basis sets with the B3LYP method, a reversion in term of energy has been observed for the two first minima in the case of the charged disaccharide in the gas phase, this was attributed to the large grid of 30 degrees that could lead to the exclusion of an intermediate value corresponding to the real minimum of energy. We thus suggest that after establishing potential energy maps it is essential to proceed to full optimizations of the lower energy conformers. Calculations using the more accurate correlated method MP2 with the 6-31G(d) basis set have also been performed for conformers of the two disaccharides in the gas phase.

Retracted Article: A highest stable cluster Au58 (C 1) re-optimized via a density-functional tight-binding (DFTB) approach.

The vibrational spectrum ω i of a re-optimized neutral gold cluster Au58 has been calculated using a numerical finite-difference approach and the density-functional tight-binding (DFTB) method. We have exactly predicted the vibrational frequency ranging from 3.88 through to 304.49 cm-1 which depends on the size and the arrangement of the atoms in the nanoparticle morphology of the cluster at ΔE = 0. Our investigation has revealed that the vibrational spectrum is strongly influenced by size and structure. It is well known that gold atomic clusters can have planar or hollow cage-like structures due to their relativistic effect. However, in our study, by first principles calculations on a Au58 cluster we have proposed that gold clusters of medium size can form a shell-like structure (skeleton/helmet), this is demonstrated by the remarkable robustness of a double shell structure with a hollow inner shell of about ten atoms. Finally, the structure symmetry (C 1) is confirmed through the cluster size, vibrational spectroscopy, and by studying the effect of temperature on a neutral gold cluster for the first time.

Theoretical study of the NLO responses of some natural and unnatural amino acids used as probe molecules.

The first hyperpolarizabilities ß of the natural aromatic amino acids tryptophan and tyrosine have been investigated using several methods and basis sets. Some of the theoretical results obtained were compared to the only experimental hyper-Rayleigh scattering data available. The sensitivity of tryptophan to its local environment was analyzed by constructing two-dimensional potential energy plots around the dipeptide tryptophan-lysine. Static hyperpolarizabilities ß(0) of the found minima were calculated by a second-order Møller-Plesset (MP2) method in combination with the 6-31+G(d) basis set. Moreover, the efficiency of tryptophan and those of a series of unnatural amino acids as endogenous probe molecules were tested by calculating the nonlinear responses of some peptides. Impressive results were obtained for the amino acid ALADAN, which shows significantly improved nonlinear performance compared to other amino acids with weak nonlinear responses.