Resolution of the Identity method

Weigend F, Kattannek M, Ahlrichs R (2009) Approximated electron repulsion integrals Cholesky decomposition versus resolution of the identity methods. J Chem Phys 130 164106... 

As is done in the HF and MP methods, computation of electron-repulsion integrals in CC calculations can be speeded up by using the density-fitting (resolution-of-the-identity) method [M. Schiitz and F. R. Manby, Phys. Chem. Chem. Phys., 5, 3349 (2003)]. 

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