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Coupled Cluster Calculations on Large Molecular Systems (LCC)
Date du début: 1 mai 2012, Date de fin: 30 avr. 2017 PROJET  TERMINÉ 

"Quantum mechanics provides the key to the understanding of the molecular world. Many years of theoretical research have made coupled cluster calculations the state-of-the-art method for small molecules, where calculations have reached an accuracy often challenging experimental results. To describe large molecular systems with coupled cluster methods, the computational scaling with the system size of existing methods represents a roadblock to progress. The ultimate goal is to obtain coupled cluster methods that scale linearly with system size and where the calculations are embarrassingly parallel, such that calculations for small and large molecular systems require the same computational wall time. This proposal describes how this goal may be accomplished. The key is to express the coupled cluster wave function in a basis of local Hartree-Fock (HF) orbitals. We have recently shown how such a local HF basis may be obtained and described how linear-scaling, embarrassingly parallel coupled cluster energies may be obtained. Here we present proof-of-concept calculations for the energy and the molecular gradient for the simple model MP2 (second order Møller-Plesset perturbation theory) and propose to use the same technology for higher level coupled cluster methods to yield not only the energy of a large molecule, but also molecular properties as the equilibrium geometry, harmonic frequencies, excitation energies and transition moments, nuclear shieldings, polarizabilities and electronic and vibrational circular dichroism. This proposal will open a new era of accurate quantum calculations on large molecular systems such as nanoparticles and proteins. The presented developments will accelerate research, not only in chemistry and physics, but in molecular science and engineering in general."