Localized orbitals for the treatment of dynamical and non-dynamical correlation

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Project objective

This project covers two principal points. The first point is about a variational method for obtaining localized orbitals. This approach has been recently proposed and implemented in a preliminary way in the Laboratoire de Physique Quantique (LPQ) of Toulouse University. Working with local orbitals induces a hierarchy in the importance of the Slater determinants in a large CI basis. This makes possible to eliminate those determinants whose weight in the CAS wave function is negligible, and to replace therefore the CAS expansion by a (usually much shorter) MR expansion. Part of the work will be to replace the variational approach with a perturbative one, the implementation of a reduced transformation of the two-electron molecular integrals and the possibility of neglecting the interaction between distant regions of the system. A second point is the application of this technique in the calculation of realistic systems covering different fields. In some electronic spectroscopy problem a local approach can produce important results. For example, in excitation processes of a cromophore group in a large molecule with a MR description of the orbitals located in the cromophore region, or in large delocalized biological systems ( e.g., the pi/pi* excitation in retinal). It is crucial to test the sensitivity of local approaches to far substituents shifts. In the study of the mixed-valence and magnetic systems the local descriptions are easier to interpret in accord to magnetic hamiltonians so that both the exchange and Coulomb parameters will be easier to get.

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Participants

• UNIVERSITE PAUL SABATIER DE TOULOUSE III · TOULOUSECoordinatorFrance

Links

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