Excited state linear response functions and two-photon transition moments between two excited states: *CCEXLR

In the *CCEXLR section input that is specific for double residues of coupled cluster cubic response functions is read in. Results obtained using this functionality should cite Ref. [192,193]. This section includes:

• frequency-dependent second-order properties of excited states
  
  $$\alpha^{(i)}_{AB}(\omega) = -\langle\langle A; B\rangle\rangle^{(i)}_\omega$$
  
  
  where $A$ and $B$ can be any of the one-electron operators for which integrals are available in the **INTEGRALS input part.
• two-photon transition moments between excited states.

Double residues of coupled cluster cubic response functions are implemented for the models CCS, CC2, and CCSD.

.ALLSTA

Calculate excited-state polarizabilities for all excited states.

.DIPOLE

Evaluate all symmetry-allowed elements of the dipole-dipole tensor of the double residues of the cubic response function (a maximum of six components for second-order properties, and a maximum of nine for two-photon transition moments).

.FREQ

READ (LUCMD,*) MFREQ
READ (LUCMD,*) (BEXLRFR(IDX),IDX=NEXLRFR+1,NEXLRFR+MFREQ)

Frequency input for $\alpha^{(i)}_{AB}(\omega)$.

.HALFFR

Use half the excitation energy as frequency argument for two-photon transition moments. Note that the .HALFFR keyword is incompatible with a user-specified list of frequencies.
For excited-state second-order properties the .HALFFR keyword is equivalent to the .STATIC keyword.

.OPERAT

READ (LUCMD,'(2A)') LABELA, LABELB
DO WHILE (LABELA(1:1).NE.'.' .AND. LABELA(1:1).NE.'*')
READ (LUCMD,'(2A)') LABELA, LABELB
END DO

Read pairs of operator labels. For each of these operator pairs, the double residues of the cubic response function will be evaluated at all frequencies. Operator pairs which do not correspond to symmetry-allowed combinations will be ignored during the calculation.

.PRINT

READ (LUCMD,*) IPRINT

Set print parameter for the *CCEXLR section.

.SELSTA

READ (LUCMD,'(A80)') LABHELP
DO WHILE(LABHELP(1:1).NE.'.' .AND. LABHELP(1:1).NE.'*')
READ(LUCMD,*) ISYMS(1), IDXS(1), ISYMS(2), IDXS(2)
END DO

Read symmetry and index of the initial state and the final state. If initial and final state coincide one obtains excited state second-order properties (or, more precisely, the difference of the excited state second-order property relative to the ground-state property), if the two excited states are different one obtains the two-photon transition moments between the two excited states.

.STATIC

Add $\omega = 0$ to the frequency list.

.USELEF

Use left excited-state response vectors instead of the right excited-state response vectors (default is to use the right excited-state response vectors).