Hi Psi4 Community,
I have what feels like a dumb question, but I can’t figure it out, so maybe you can help me!
Things that work: I am trying to build a tutorial on CI. I am using the psi4API in python (which is amazing). I am motivating the need for correlation with the failure of HF to get singlet and triplet energies correct for H2 dissociation. I can plot singlet and triplet surfaces and triplet is lower than singlet, as expected. Then, CISD fixes the problem like it should. Yea! So far, so good.
I see how to get the updated wavefunction
Where I am stuck: I want to show the uncorrelated nature of the wavefunction in HF and the correlation added by CI. I want to plot the two-electron wavefunction amplitude in real-space \Psi(r1,r2) for the HF and CI wavefunctions. I want to show that in HF the amplitude of two electrons to be on the same nucleus is high for all distances but CI fixes that. I don’t see how to get this!
What I have tried: I have looked through the tutorials and Psi4 lab experiments for some hints, but I don’t see anything helpful. I have looked through the documentation that I could find - traversing help(psi4), help(psi4.core), help(psi4.core.Wavefunction), help(psi4.core.MintsHelper), and a bunch of others. I have learned a lot but not the easy thing I am looking for! (At least I don’t recognize it as such!)
This thread is very similar to what I am looking for
but it is for the density. I want to put in all the electron coordinates and get the total wavefunction amplitude (3N cartesian coordinates as inputs and one number as an output).
My current work around: I have made a cartoon by showing 1-D cuts through sigma and sigma* MOs (from 1s AOs) and show that the double excitation sigma* (times) sigma* added to the ground state reduces the chance for both electrons to be on the same atom. BUT I would love to show that happening with the CISD wavefunction as a function of r_AB.
Sorry if I missed something obvious! Any help is welcome! Thanks!