RHF CCSD(T) analytic gradients

I’ve been trying to run CCSD(T) optimizations and found that the analytic gradients aren’t available:

“PsiException: select_ccsd_t__gradient: Method ‘ccsd(t)’ with CC_TYPE ‘CONV’ and REFERENCE ‘RHF’ not available”

I am running these with a RHF reference (these are singlet systems). If I run these as UHF, then the analytic gradients are available. I'm wondering why this is happening.

I am running a (very recently updated) copy of the binary.

Hi Kevin,

Could you provide me the input file that you are using. Also could you tell me the binary version as well.


Thanks. Below is the version of the input that works (UHF). If I change UHF to RHF, then I get an error. I’m not sure about the version of the binary, but I downloaded it three days ago.

memory 60000 mb

molecule ch2 {
0 1
c 1 1.200
h 2 1.089 1 180.0
n 3 2.000 2 180.0 1 180.0
c 4 1.200 3 180.0 2 180.0
h 5 1.089 4 180.0 3 180.0

set {
reference uhf
basis cc-pvdz
dertype first


I could run the input file with reference ‘RHF’ successfully with the latest version of psi4.
“psi4 --version” would give you the binary version. It seems you need to update your binary.

Thanks. The version I have is: 1.0.54

to be clear, the program runs successfully with rhf (there isn’t actually an error), but the finite difference method is used instead of analytic gradients.

Yup, thats expected. When I said I can run the input successfully for RHF with latest version of psi4, I meant using analytic gradients. Your version of psi4 doesn’t have analytic rhf-ccsd(t) gradients, which is why it is invoking finite difference calculations.

Yes, this is a psi4 version issue. You may have acquired or updated psi4 recently, but conda update psi4 only grabs stable releases, the last of which (1.0.54 for Linux conda builds) was July 2016. In development terms, we’re up to ~1.1rc1 from April 2017, but because it’s not a stable release, you have to grab it off the devel subchannel. Follow these directions:

Thanks a lot. I got this up and running and it’s running perfectly.