CCSDT calculation of F2 at twice equilibrium distance cannot converge


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When the basis set is increased to aug-cc-pvtz, the total energy of CCSDT of CH is lower than the result of the same method using CBS/mix basis set extrapolation in an article by Drs. in EMSL at that stage, and all thsoe obtained by GAMESS are from 0.0106 to 0.00886 hartrees from that, but both will cause negligible spectroscopic constants differences from the calculated and the experimental data indexed, according to the article, perhaps the geometry provided by the GAMESS example is better.

The CCSDT total energy with NWCHEM6.8 in the case of aug-cc-pvtz is further 0.00005 hatrees lower using the mp2 optimized CH geometry by GAMESS 2018 R3, perhaps because of a larger basis set, which of cause will also be anticipated to produce a very good agreement.
The active space coupled cluster total energy of CH3 with aug-cc-pvtz using GAMESS might be much less hardware demanding, thus much faster, than that obtained by CCSDT using NECHEM to match experimental physical quanties very well.

Congratulations for the achievement of efforts from authors and editors of both programs in GAMESS and NWCHEM.