I would like to verify how a complete basis set limit is computed. In my input I have the following line:
energy(cbs, corl_wfn='mp2', corl_basis='aug-cc-pv[tq]z', scf_basis='aug-cc-pv[dtq]z', corl_scheme=corl_xtpl_helgaker_2, scf_scheme=scf_xtpl_helgaker_3)
At the end of the run, the log file includes these lines:
==> Stages <==
scf hf / aug-cc-pv[dtq]z 1 -193.21347417 scf_xtpl_helgaker_3
corl mp2 / aug-cc-pv[tq]z 1 -194.08699951 corl_xtpl_helgaker_2
corl hf / aug-cc-pv[tq]z -1 -193.21831488 corl_xtpl_helgaker_2
It is clear that the scf limit, obtained from the use of three basis sets, was computed using Helgaker’s exponential equation (scf_xtpl_helgaker_3).
Now here is my desire for confirmation - for the correlation energy, was the Helgaker’s power equation (data from two basis sets, i.e. corl_xtpl_helgaker_2) used for computing both the MP2 total energy (-194.08699951) and the HF total energy (193.21831488)? The reason I ask is because there is another exponential extrapolation option in the manual for computing the scf component using the data from two basis sets, which is scf_xtpl_helgaker_2.
Another small question. The final extrapolated correlation energy reported to be:
==> CBS <==
corl mp2 / aug-cc-pv[tq]z -0.86868463 corl_xtpl_helgaker_2
In Psi4, is this final computed value obtained by taking the difference in the above total energies in the
==> Stages <== section, or was the correlation energy here directly extrapolated (corl_xtpl_helgaker_2) using the reported
Correlation Energy found in each of the individual basis set calculations?
Thanks in advance,