Second order nonlinear optical properties of corroles: experimental and theoretical investigations

The first hyperpolarizabilities, βHRS, of corrole derivatives have been measured by using Hyper–Rayleigh Scattering technique. The results showed that βHRS of corroles could be greatly enhanced by modifying its periphery with donor–acceptor groups. Maximum value reaches 354 × 10-30 esu at an incident wavelength of 1500 nm. βHRS of investigated corroles were also calculated with the Zerner's intermediate neglect of differential overlap/configuration interaction/sum-over-states method. The calculated and experimental results are in good agreement and conclude that βHRS arises mainly from the charge transfer along molecule's non-symmetrical axis and strong coupling between two different excited states of the Soret band.

A Theoretical Structure Study Infrared Spectra of C60O Isomers Through Ab Initio Method

The infrared spectra of C60O isomers have been calculated through ab initio method. It has been observed that the simulated spectrum of one of C60O isomers is matching with the available experimental data in literature, while the other isomers are not matching so much. One can easily understand the basic physical properties of C60O by knowing of their vibration and geometric structures with their interrelation between these properties. It is found that the isomeric structures of C60O are very sensitive to electron correlation treatment with basis set that are employed. So the structure of C60O will not calculate from semi-empirical methods such as modified neglect of differential overlap (MNDO) or AM1 for more accuracy. The simulated spectra show different bands that rarely found all bands simultaneously in single experiment.

Theoretical Prediction and Experimental Confirmation of Charge Transfer Vibronic Excitons and Their Phase in ABO3 Perovskite Crystals

The current theoretical and experimental knowledge of new polaronic-type excitons in ferroelectric oxides - charge transfer vibronic excitons (CTVE) is discussed. It is shown that quantum chemical Hartree-Fock-type calculations using a semiempirical Intermediate Neglect of Differential Overlap (INDO) method (modified for ionic/partly ionic solids) as well as photoluminescence studies in ferroelectric oxygen-octahedral perovskites confirm the CTVE existence. Our INDO calculations for KTaO3 and KNbO3 have demonstrated that the triplet exciton is a triad centre containing one active O atom and two Ta atoms sitting on the opposite sites from this O atom. The total energy of a system is lowered by the combination of Coulomb attraction between electron and hole and the vibronic effect in this charge transfer vibronic exciton. It is shown by means of our INDO calculations that polaronic-type CTVE in ferroelectric oxides could lead to the formation of a new crystalline phase. The ground state energy of this phase consisting of strongly correlated CTVEs lies within an optical gap of a pure crystal, and is characterized by a strong tetragonal lattice distortion, as well as by the ferroelectric ordering.

Calculations of the Electronic and Atomic Structure and Diffusion of Point Defects in KNbO3 Perovskite Crystals and Relevant KTN Solid Solutions

In this paper we review our recent achievements in large scale computer simulations of point defects in advanced perovskite crystals. We have calculated the defect migration energies in the KNbO3 cubic phase using quantum chemical method of the Intermediate Neglect of Differential Overlap (INDO) and classical shell model (SM). The migration energies for the O vacancy obtained by means of these two quite different methods are reasonably close (0.68 eV and 0.79 eV, respectively) and also agree with the only experimental estimate available (ca. 1 eV). Atomic relaxations calculated by these two methods also agree quite well. We used INDO method for a large-scale modeling of the atomic and electronic structure of KNbxTa1-xO3 (KTN) perovskite solid solutions. Results for periodic defect model (large unit cell) of 40 and 320 atoms are compared with 135-atom INDO cluster calculations. Periodic Nb impurities in KTaO3 reveal clear off-center displacement beginning with the smallest calculated concentrations, so does an isolated Nb impurity in a cluster INDO calculation. The magnitude of this displacement is close to the EXAFS observation (0.27 a.u.).