UNO CI studies of nonlinear optical properties and excited staes of unstable molecules and clusters

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In this research project, our UNO-CI computation method has been incorporated into the Alchemy II program package in order to calculate potential curves, excitation energies, transition probabilities, etc.for unstable molecular systems. The UNO CI method has been applied to depict the potential curves of the linear Hn systems and the dimer of triplet methylene. The UNO CASSCF calculations have also been carried out for these systems. It has been established that the UNO-CI wavefunction is a very good trial for the UNO CASSCF calculation. Thus, the computation scheme without external electromagnetic fields has been established.Next, a new method, numerical Liouville approach (NLA), has been proposed in order to investigate the frequency-dependent nonlinear optical responce of molecules and molecular clusters under the strong laser fields. The numerical stability and computational reliability of the NLA method have been examined in details. The NLA method has also been applied to calculate the hyperpolarizabilities of polyenes. The results are in consistent with the experiments in both the off-resonant and resonant regions.Ab initio MO calculations have been performed for clusters of DNBB in order to elucidate factors which determine its crystal structure. It has been found that the hydrogen bonding interaction is the most important factor to control the crystal structure. It is concluded that the effective use of hydrogen bondings is essential for crystal engineering approach towards molecular-based materials.