Dear all:

On Tue, 18 Dec 2001, Alessandro Bagno wrote:

> Hi ADF fellow users:
> I have started to run ADF recently, especially the NMR module.
> The two questions:
> (1) When I calculate the shieldings of highly symmetric molecules, the
> values of symmetry-equivalent nuclei are sometimes rather different even
> though a single-point calculation perceived the correct symmetry. This
> holds particularly for the paramagnetic component. Any hint?
>
> (2) I have tried NMR calculations using a TAPE21 obtained from a COSMO
> job. The job completes correctly and the shieldings are different from
> those in the gas phase, but is this **meaningful**?
>
> Thanks for any help.

Answer,

Regarding (1):
Thanks for bringing in this bug.
I have tested the NMR module, and indeed the symmetry-equivalent nuclei
sometimes give rather different shieldings.
As far as I have seen this happens only if symmetry (higher than nosym)
is used in the adf-calculation of the molecule and at the same
time frozen core basis sets are used.
After some testing I found that this is due to a bug in the NMR module,
which does not treat this situation always correctly.
The core orthogonalization coefficients are not
treated correctly in this case. These coefficients are often
small, and therefore the errors due to this bug will not always be large.
One can avoid this bug by using symmetry nosym in the adf calculation.
Another way to avoid this problem is to use all electron basis sets,
in which case one can use symmetry (higher than nosym) in the adf calculation.

Regarding (2):
The results with the COSMO job do not give meaningful results
for the NMR module. The COSMO potential is not correctly included
in the NMR module.

Best regards
Erik van Lenthe
------------------------------------------------------
Afdeling Theoretische Chemie, Vrije Universiteit,
De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
Tel. : +31 20 44 47615
secretary: 44 47519
 fax.: 44 47629
 e-mail: vlenthe_at_chem.vu.nl
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Received on 2001-12-20 15:07:04