NMR shift calculations with COSMO

[janap]

Is it possible to run calculations of NMR chemical shifts in the presence of COSMO solvent? That is - are GIAO + COSMO coupling terms implemented in Turbomole?

I know it's available in g03 but g03 is rather slow for my purpose ...

[uwe]

Hello,

COSMO is currently not implemented in mpshift. You will simply get an error message when you try it.

However, you could try to run a geometry optimization with COSMO, remove the $cosmo keyword from the control file and then run mpshift (remember to set the size of the twoint file in $scfintunit to a non-zero number when you do Hartree-Fock or use a hybrid functional).

I am far away from being an expert, but I guess that since the geometry and the molecular orbital have been computed with COSMO, the missing terms in the GIAO algorithm will be much smaller than the contribution you have included. Just give it a try if you can compare to experimental results.

Regards,

Uwe

[janap]

Thanks Uwe for your comment. I did what you advised me to do but I obviously get wrong results. I ran the same claculation with Gaussian many times before and I also have a hint from experiment, so I know approximately what numbers I should get.

The results of the 31P chemical shielding tensor in dimethylphosphate are:
-----------------------------------------------------------------------------------------
                     iso                  11             22             33
from g03      289.5           176.1        231.0          461.4
from TM         70.1           -81.9          -9.7          301.9

Strangely, I actually get the wrong results with gaussian as well but only if CPCM is used. With PCM and IEF-PCM keywords, my results are OK.
The same problem happens if I calculate the wavefunction in Turbomole and use the orbitals obtained to compute the shielding tenso in MAG with GIAO. On the contrary, wavefunction in Turbomole + shielding calculation in MAG with IGLO for gauge origin gives correct results.

So it doesn't seem to be just a Turbomole-bound problem, I don't know what I should think of that  Any idea?

Thanks a lot 

Jana
 

[uwe]

Hi Jana,

dimethylphosphate? I have tried it, used B3-LYP, def-TZVP basis set, C1 symmetry.

Gas phase:

ATOM  p    3      ISOTROPIC:    302.3316402       ANISOTROPIC:    206.5928077
  total magnetic shielding:
    Trace =    302.33164022
    Tensor :
             354.88930968       105.84710904        -0.06198524
             110.42662899       297.53037250         0.39775309
              -0.23001188         0.58536927       254.57523849

Gas phase geometry, single-point COSMO calculation:

ATOM  p    3      ISOTROPIC:    298.8953214       ANISOTROPIC:    177.4833376
  total magnetic shielding:
    Trace =    298.89532140
    Tensor :
             350.76987979        90.12337352        -0.03473749
              91.82104276       287.30184845         0.32949959
              -0.25463815         0.50951864       258.61423595

Finally, optimized geometry with COSMO:

ATOM  p    3      ISOTROPIC:    299.4545554       ANISOTROPIC:    175.5218084
  total magnetic shielding:
    Trace =    299.45455542
    Tensor :
             348.83998562        92.12898188        -0.06244784
              88.85976003       290.57082554         0.71849355
              -0.42249537         1.17594918       258.95285509


The difference is just about 2 ppm between gas phase and COSMO, and I do not get completely wrong results as you did. If you want, you can send your input files to the Turbomole Support.

Regards,

Uwe

[janap]

Hi Uwe,

thanks for your response and results of your calculations. After reading your post, I ran numerous test calculations and it appears that the problem is in my basis set.
I normally use IGLO-III downloaded from EMSL. If I use def-TZVP instead (as you did), everything is OK.

Strangely, all those problems with my results only appear when COSMO is switched on. Calculations without COSMO employing IGLO-III provide results I expect to get (i.e. isotropic chemical shielding somewhere around 300 ppm). Thus, the problem is not a bad choice of a basis set , just something goes wrong when IGLO-III and COSMO are used tohether, but no idea what 

J.

[janap]

Hello,

COSMO is currently not implemented in mpshift. You will simply get an error message when you try it.

However, you could try to run a geometry optimization with COSMO, remove the $cosmo keyword from the control file and then run mpshift (remember to set the size of the twoint file in $scfintunit to a non-zero number when you do Hartree-Fock or use a hybrid functional).

I am far away from being an expert, but I guess that since the geometry and the molecular orbital have been computed with COSMO, the missing terms in the GIAO algorithm will be much smaller than the contribution you have included. Just give it a try if you can compare to experimental results.

Regards,

Uwe

Hello,

I was just wondering whether something changed since 2008 when I posted here last time. Has COSMO been implemented in MPSHIFT in the meantime or not?

Thanks,
Jana

[uwe]

Hello,

COSMO development currently is being done in other directions than NMR shieldings. I am afraid that the answer to your question is no.

Regards,

Uwe