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In addition to the above mentioned prerequisites ground-state
energy calculations with the `ricc2` module require only the
data group `$ricc2` (see Section 15.2.13), which defines
the methods, convergence thresholds and limits for the number
of iterations etc. If this data group is not set, the program
will carry out a CC2 calculation.
With the input
$ricc2
mp2
cc2
conv=6

the `ricc2` program will calculate the MP2 and CC2 ground-state
energies, the latter converged to approximately 10^{-6}a.u.
The solution for the single-substitution cluster amplitudes
is saved in the file `CCR0--1--1---0`

, which can be kept
for a later restart.

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