The development of quantitative molecular orbital theory for mesoscopic systems and its application to the initial chemical process of vision

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The mesoscopic system includes many important systems, from chemical point of view, as solute-solvent systems, molecular-surface systems, extended systems, and cluster. The aim of the present research was to develop a quantitative molecular orbital theory and a program package for the mesoscopic system and to apply them to the initial chemical process of vision. The focus was especially on the following topics : 1. Development of multiconfiguration SCF and Kohn-Shem DFT methods for large-scale systems, 2. Development of electron correlation methods for large-scale systems, in particular a multireference based perturbation theory MC-QDPT, and 3. Studies on the electronic structure and chemical reaction of large-scale systems.1. In ab initio MO theory, an efficient scheme for determining MOs is crucial. First we have developed a highly efficient molecular integral algorithm and program, which is essential as the initial step of MO determination, and then developed QCAS-SCF, string-product space SCF, and general MC-SCF methods. These MC-SCF methods treat only chemically important electronic configuration and thus more effective than the CAS-SCF method, the conventional MC-SCF method. We have also presented Kohn-Sham DFT method for large-scale systems, using non-orthogonal localized MOs.2. For the inclusion of electron correlation effect, we developed QCAS-QDPT, GMC-QDPT, MROPT-PT, and MR-Brillouin-Wigner PT. These PTs are based on the compact wave functions developed in the previous term, and therefore they are applicable to large-scale systems.3. With these MC-SCF and perturbation methods, we have made the following applications to molecules including large-scale systems : Design of multiply charged anions, analysis of the neutral-ionic transition of CT compounds, identification of highly excited states of five-membered ring compounds, and electronic structure of long polyenes.