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For RI-CC2 calculations,
the operation count and thereby the
CPU and the wall time increases--as for RI-MP2 calculations--approximately
with
(*O*^{2}*V*^{2}*N*_{x}), where *O* is the
number of occupied and *V* the number of virtual orbitals
and *N*_{x} the dimension of the auxiliary basis set for
the resolution of the identity.
Since RI-CC2 calculations
require the (iterative) solution of the cluster
equations (9.5) and (9.6), they are about 10-20 times more
expensive than MP2 calculations.
The disk space requirements are approximately
*O*(2*V* + *N*)*N*_{x} + *N*_{x}^{2} double precision words.
The details of the algorithms are described in ref. [10], for
the error introduced by the RI approximation see
refs. [86,104].

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