Transition moments between two excited states: *CCQR2R

In the *CCQR2R section the input that is specific for coupled cluster response calculation of excited state-excited state electronic transition properties is read in. This section includes presently for example calculation of excited state oscillator strength. The transition properties are available for the models CCS, CC2 and CCSD, but only for singlet states. The theoretical background for the implementation is detailed in Ref.
citeChristiansen:CCLR,Christiansen:QEL. This section has to be used in connection with *CCEXCI for the calculation of excited states.

.DIPOLE

Calculate the ground state-excited state dipole (length) transition properties including the oscillator strength.

.DIPVEL

Calculate the excited state-excited state dipole-velocity transition properties including the oscillator strength in the dipole-velocity form. (The dipole length form is recommended for standard calculations).

.NO2N+1

Use an alternative, and normally less efficient, formulation for calculating the transition matrix elements (involing solution of response equations for all operators instead of solving for the so-called $N$ vectors which is the default).

.OPERAT

READ (LUCMD,'(2A8)') LABELA, LABELB
Read pairs of operator labels for which the residue of the linear response function is desired. Can be used to calculate the transition property for a given operator by specifying that operator twice. The operator can be any of the one-electron operators for which integrals are available in the **INTEGRALS input part.

.SELEXC

READ(LUCMD,*) IXSYM1,IXST1,IXSYM2,IXST2
Select which excited states the calculation of transition properties are carried out for. The default is all states according to the CCEXCI input section (the program takes into account symmetry). For calculating selected states only, provide a list of symmetry and state numbers (order after increasing energy in each symmetry class) for state one and for state two. This list is read until next input label is found.