Employing Frozen Core in Calculating Relaxed Dipoles from DF-MP2

[dmm219]

Hello,

Two simple questions:

1. When one uses the properties module for DF-MP2 to calculate the dipole moment, is the default to use the relaxed OPDM?

2. If 1. is yes, can the frozen core approximation be used?

Background:

I am using both v1.4a2 and 1.3.2.

I can see from the docs that for v1.3.2 and v1.4rc3.dev11 that the default has been set to relax OPDM.

I just want to confirm that this is true when using the properties module.

In a prior post on CSSD properties it is stated that:

@ashutosh

Also, you can’t
use frozen core for calculating relaxed densities as it has not been implemented in PSI4 .

But later in the thread it seems like this only refers to CC:

@ashutosh

Unfortunately, there is no way of getting relaxed CCSD densities/properties with frozen core as of now since we haven’t coded frozen core contributions to orbital relaxations. Frozen core CC gradients is definitely on our TODO list and we would try to implement it soon in PSI4.

So, I found myself a bit confused about the state of employing the frozen core approximation in DF-MP2 property calculation.

I can provide a simple input to illustrate exactly what I am doing, if needed to address this.

Thanks in advance!
Devin

[jmisiewicz]

Ashutosh’s posts are talking about a specific technical issue in Psi4. I can go into details if you want (dealing with this is on my to-do list!) but the short of it is that our analytic gradient code for conventional integrals cannot handle the frozen core approximation, so frozen core densities aren’t implemented. This is not the case for DF-MP2, which uses DF integrals.

1. Yes, the default is to use the relaxed OPDM, whether using the properties function or not.
2. Yes, the frozen core approximation can be used. Orbital relaxation includes the additional frozen core terms, and I’ve personally correctness-tested this. You get exactly the same dipole as if you compute the dipole with a “finite field” approach.

[dmm219]

Great! Thanks for the speedy response and clarification.