Error with transition metal calculations?

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1 week 6 days ago #1196 by bparseghian
I am getting inaccurate results for CCSD(T) calculation on Br as compared to CCCBDB and a couple of other software packages.  The input file is:

basis=aug-cc-pVTZ
calc=CCSD(T)
mem=5000MB
core=frozen
scftol=8
unit=angs
geom=xyz
1

   Br        0.0000000000    0.0000000000   -0.0755311173

The HF energy is correct; but both the MP2 energy and CCSD(T) are not.  I have been trying to figure out the problem with no success.

I ran the same calculation for Cl with no issues (HF, MP2, CCSD(T) match benchmarks).  I also ran Ca using a cc-pVTZ basis set with no issues (HF, MP2, CCSD(T) match benchmarks).

I ran Br all electron (core=corr) with no issues (HF, MP2, CCSD(T) all match benchmarks).  That led me to wonder whether there was an issue with frozen core.

But then I tried Sc with both all electron and frozen core, and HF, MP2 and CCSD(T) were all inaccurate.

I also tried without density-fitting approximation (ccprog=mrcc, dfbasis_scf=none, and dfbasis_cor=none), which did not solve the problem.

I also tried different basis sets and used freshly downloaded basis sets with no success.

I would greatly appreciate any assistance.

Regards,

Berj
 
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1 week 6 days ago #1198 by kallay
In mrcc, only the 4p electrons of Br are correlated, while in other programs, the 4s and 3d electrons can also be correlated. Please set core=9 to reproduce those results.

Best regards,
Mihaly Kallay

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1 week 6 days ago #1199 by bparseghian
Thank you very much. That was exactly the issue. For these types of calculations, it seems like MRCC's default frozen core for Br (core=14) is more appropriate to the cc basis sets that are being used than the other programs. But it is helpful to have the flexibility.

Thank you, again.

Regards,

Berj Parseghian

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