@bozkaya, are you saying that calling energy('ccsd(at)') will give me a DF-Lambda-CCSD(T) density matrix? I know for other coupled cluster methods in psi4, you have to call gradient to get a density.
@bozkaya that’s what I figured. I’m sure implementing the gradient is a significant amount of work!
That being said, is there any reason that I couldn’t just construct the density matrix from the returned wavefunction from energy using psi4numpy? I don’t need the gradient, just the density itself.
In order to form PDMs you need to T- and Lambda-amplitudes, which are written to disk, not saved to wfn. Hence, you cannot get them from returning wfn. However, if you disable psi.clean() function you may try to read them in from the DFOCC files. @joshrackers
I’ll warn you that to get the same density matrix as from gradient theory, at the very least, you would also need to solve the orbital Z-vector equations. An unrelaxed density matrix might be doable, though.
Anyways, this topic seems answered now. It’s good practice to mark a post as “solving” the topic when it’s answered, so that way we know there’s nothing else we need to do here. There should be a checkbox on each post to mark it as “solving” the topic.