Community Research and Development Information Service - CORDIS

Periodic Report Summary 1 - NEWQUANTUM (Development of multi-level electron correlation methods in quantum chemistry)

The development of multi-level coupled cluster models is progressing according to plan. The theoretical foundation is now fully developed and published in the Journal of Chemical Physics. In particular I have implemented excitation energies for the CC2 and CCSD models and the results look convincing. The numerical data was obtained using a pilot implementation and we currently working on the production code.
Currently we are also working on the incorporation triple excitations as treated in the CC3 model and the new production code can treat one part of the molecule at the CC3 level and the others at the CCSD level. Both total energies and excitation energies have been implemented and we have obtained huge computational savings as compared to the full CC3 model. Treating only a small part of the molecule at the CC3 level we are able to obtain full CC3 accuracy in a fraction of the computational time need for the full CC3 model. The results of this production implementation have been submitted to The Journal of Chemical Physics.
We have also developed multi-level methods for NEXAFS spectra and have in this way obtained very nice results. This implementation has been applied to several test molecules and these results are now published. Special approximation techniques had to be developed in this connection and these will be reported within the next month. These developments have also spurred new collaborations with experimentalist at SLAC and I have participated in a project where NEXAFS spectra are recorded for molecules in electronic excited states. These are so-called pump-probe experiments and the system we investigated was thymine that was planned in the proposal. The research results will be submitted to Science shortly.
Several new projects have been started in collaboration with the Martinez these focus on the development of coupled cluster theory that can be used for excited states at conical intersections and also a novel approach to treat electron correlation. These results will be submitted shortly. I am also working on developing integral approximations along the lines of Cholesky decomposition and THC. Results should be ready with the next six months.

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Life Sciences
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