Ar atom and CI - surprising result

Subject:

if B is 1s22s22p1, what is Li?

Passfield:

Comments:
: Dear Molcasers! : To make the story as short as possible: : I take Ar atom, ANO-L basis set, with the default contraction pattern, and then 3 times perform single reference CI using different orbitals. The results are quite astonishing for me... : 1) HF >> SRCI(8), : that is single reference CI on top of the HF. In CI I excite only 8 electrons, 1s2s2p are frozen in Motra. The energy is -257.0435... and is quite similar to that reported by prof. Roos in 1991 ... : 2) HF >> CAS(8,8) with 1s2s2p FROZEN >> SRCI(8), : that is the same CI, but after HF I make CAS, where 1s2s2p are treated as totally frozen orbitals... The energy is -257.0435... Looks fine. : 3) HF >> CAS(8,8) with 1s2s2p INACTIVE >> SRCI(8), : which basically is exactly the same as 2), but I wanted to have even better orbitals, so I didn't freeze 1s2s2p but rather made them inactive. The energy is -257.017.... : : What's wrong with 3) ? Why I get so artificial energy? : For 2) and 3) I use exactly the same input files which have only one difference: for 2) I have 5 Frozen and 0 Inactive, and for 3) I have 0 Frozen and 5 Inactive in CAS...In Motra there are always 5 Frozen. : Shouldn't I get the best orbitals for CI from number 3? : Regards, : Pawel Wielgus