Want to know about the OD(T) method

Questions
#1

I want to know about the OD(T) method implemented in Q-chem. There is no reference to this method if I am not wrong. Is it \Lambda OCCD(T)? even for the T_3 (\Lambda_3) part? Also, the output file prints “doing only closed-shell triples contributions”. What does that mean? I am doing ground state energy calculations for very small closed-shell atoms.

#2

OD itself is orbital-optimized CCSD, which is described here:
https://manual.q-chem.com/5.3/topic_odcc.html
Then OD(T) is the usual perturbative approximation for triples on top of OD, as is mentioned briefly here:
https://manual.q-chem.com/5.3/Ch6.S9.SS1.html

#3

Thank you, prof John Herbert, for replying. So, basically, the triple contribution is not optimized, added on top of the OD method.

#4

I believe that’s correct but it’s not my code so to be absolutely certain you should check the papers cited in the manual.

#5

You are absolutely correct. I could fully reproduce the ground state energy for the OD method as well as for the OD(T) method as implemented in Q-CHEM. However, I am looking for a fully optimized OO-CCD(T), which is not available in any commercial package yet.

#6

What do you mean by “fully optimized”?

#7

I mean to say even for the T_3 part taking account of \Lambda_3 as reported in this paper https://doi.org/10.1063/1.4720382 by Uğur Bozkaya and Henry F. Schaefer III

#8

Pretty sure this is just OD(T), like it says…