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The bond length alternation (BLA )of increasingly long oligomers by using six hybrid functionals and the Hartree-Fock model is calculated. It is shown that inclusion of self interaction corrections (SIC)dramatically improves the computed BLA (compared to pure-DFT) for medium chain lengths.

The visible spectra of a large panel of thioindigo dyes are evaluated with the polarizable continuum method (PCM) and time-dependent density functional theory (TD-DFT), using the PBE0 functional and extended atomic basis sets. It is found that the majority of the cis thioindigo dyes are planar and their hypso-character originates from repulsion of electron densities in the excited state, and the central C=O double bond length is a good indicator of the color of the substituted thioindigo

The bond of alternation of 30 series of increasingly long linear oligomers for a total of more than 250 compounds is investigated at the second-order Moller-Plesset level. The variations that are induced either by chemical substitution of the backbone atoms or configurational modifications are discussed.

The structures and the properties of polyaminoborane oligomers by using ab initio computational tools including dynamic electron correlation effects are investigated. The variations of the properties upon conformation changes are studied.

Density functional theory schemes based on conventional exchange-correlation functionals have been used to establish dipole moment, polarizability, and first and second hyperpolarizabilities of push-pull pi-conjugated systems. It is concluded that current exchange-correlation functionals do not accurately describe the polarization of conjugated systems when the polarization is the result of donor/acceptor substitution or an external field or both.

The microsolvation of protonated L-alanine with one, two or three water molecules is examined by using a MP2/6-311++G(d,p) approach. The results have shown that many di- and trihydrated complexes should coexist under the experimental conditions.

A reliable and fast computational method developed for the calculation of p[K.sub.a]* of photoacids is examined. The results obtained from the five coumarins verify the reliability of the model that is developed by combination of density functional theory (DFT) for the excited states, time-dependent DFT, with a polarizable continuum model for solvent.

An ab initio procedure relying on the combination of time-dependent density functional theory and polarizable continuum model is used for calculating the n -> [pi.sup.*] transitions in more than 100 thiocarbonyl dyes. The pros and cons of the most widely used hybrids, as well as the role of f polarization functions are discussed.

The ultraviolet absorption spectra of coumarins and chromones are investigated with the PCM-time-dependent-density functional theory (PCM-TD-DFT) theoretical scheme by using three hybrid functionals and taking into account methanol or ethanol solvation effects. The results have shown that there are at least two allowed excited states presenting strong oscillator strength in the UV region, where both involve a charge transfer from the benzenic cycle to the pyranone moiety.

The UV/visible spectra of a series of indirubin, isoindigo, and other indigo/thioindigo related dyes are evaluated in various solvent environments by using the time-dependent density functional theory in conjunction with the polarizable continuum model. It is stated that even for molecules of the same family, significant differences in the excitation processes are noted.

The linear and nonlinear optical properties of trans-cisoid saturated and unsaturated polyaminoborane/polyphosphinoborane alternating copolymers are studied at the MP2/6-311G(2d)//PBE0/6-31G(2d) level of approximation, by using the increasingly large oligomer series methodology. The evolution with chain length of geometry parameters, partial atomic charges, electric dipole moments, polarizabilites and first hyperpolarizabilities of both phosphorus-and nitrogen-terminated chains is reported.