aug-cc-pVXZ is basis set for general purpose, you need to note that in order to perform F12 calculation, you have to use the basis sets specifically optimized for F12 method, such as aug-cc-pVDZ-F12. You can easily find examples of CCSD(T)-F12 calculation in ORCA manual.

Thank you Dr. Liu for your response. I have gone through the ORCA manual but couldn't spot any examples for CCSD(T)-F12 calculation. Can you kindly help me out with some input examples.

A simple example is attached. More information can be obtained by searching "F12" in the manual.

Thanks a lot Dr. Lu.

I am sure your information will solve my problems.

Please, can you help me with understanding in what level it is calculated?

Here you write two basic sets

! CCSD(T)-F12/RI cc-pVDZ-F12 cc-pVDZ-F12-CABS cc-pVTZ/C pal4,

I understand that there are actually only three options:

1) calculated at the F12-CCSD(T)/cc-pVDZ level,

2) at the F12-CCSD(T)/cc-pVTZ level,

3) at some "intermediate" level between F12-CCSD(T)/cc-pVDZ and F12-CCSD(T)/cc-pVTZ.

I would like to know at what level the calculation takes place.

Thank you very much in advance!

Arina Khrapunova

Dear Arina,

Obviously, in the input file provided by Professor Tian Lu, the cc-pVDZ-F12 is considered as the orbital basis set while cc-pVTZ/C is utilized as the auxiliary basis. Additionally, please note that cc-pVDZ-F12 is used for CABS, as well. Within a F12 calculation, not only an orbital as well as a correlation fitting basis is required but a CABS basis set (a near-complete auxiliary basis set) should also be employed.

A detailed and comprehensive explanation is provided in the Orca manual.

I hope you find above-mentioned comments helpful.

Sincerely,

Saeed