ccsd IR intensities in VSCF/VCI ?

[iri...@verizon.net]

Dear Molpro experts,

I am learning to use the VCI module in Molpro (v 2024.1).  A calculation based upon Hartree-Fock went smoothly, including the dipole intensities for the combinations and overtones.  But when I change the method to CCSD, all VSCF and VCI intensities are printed zero.  The harmonic intensities are non-zero, so the dipole function appears to be available for CCSD. Is an additional directive needed to obtain intensities in VCI?  (I am interested in Fermi resonances for this problem.) 

Thanks for any hints!

-Karl

[rauhut]

Dear Karl,

once you are interested in IR intensities beyond Hartree-Fock, you need to do two things: (1) Provide the calculation of dipole moments by "CPHF,1" in the electronic structure calculation and (2) activate reading the respective Molpro variable by the INTENSITY directive of the XSURF program, that is: INTENSITY, DIPOLE=2. The first example in the XSURF section of the Molpro manual shows you an example for MP2, which you may simply alter to CCSD. Note, you can compute dipole surfaces only for those methods, for which analytical gradients are available.

Best,

    Guntram