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The calculation of excitation energies is initiated by the
data group $excitations in which at least the symmetries
(irreducible representations) and the number of the excited states
must be given (for other options see Section 14.2.13).
With the following input the ricc2 program will calculate the
lowest two roots (states) for the symmetries and
of singlet multiplicity at the CIS, CIS(D) and CC2 level with default convergence thresholds.
Ground-state calculations will be carried
out for MP2 (needed for the CIS(D) model and used as start guess for CC2)
The single-substitution parts of the right eigenvectors are stored in
where s is the number of the symmetry class (irreducible
representation), m is the multiplicity, and xxx the
number of the excitation within the symmetry class. For the left
eigenvectors the single-substitution parts are stored in files named
-xxx. These files
can be kept for later restarts.