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I am trying to compute the NMR shift for a specific atom in the middle of the surrounding crystal unit cell (1 surrounding anion sphere and 1 cation sphere) in Gaussian09. I only need the chemical shift for the middle atom.

How can I only compute the shift for this atom, and leave out the rest? And would it even save any computation time if I did?

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Short answer, you can't.

It might save a bit of time, but probably not much. The calculation would still need to go through the normal SCF on the entire system to calculate the NMR shifts.

In principal, in evaluating the property calculation, you could save a small amount of time by only computing the one atom, but for most systems, I would think the overall SCF calculation would be vastly greater than computing a few properties.

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As far as I understand the very procedure that is used to calculate NMR chemical shifts, that should not be possible. The magnetic field is basically treated as perturbation and a set of coupled-perturbed SCF (HF or DFT) equations is solved to find the response of the density matrix with respect to the field.

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  • $\begingroup$ Agreed. I would think it's possible to perform the evaluation at one point in space (i.e. one atom) rather than all atoms. It's not implemented in Gaussian or other programs and I doubt it would have much performance savings. $\endgroup$ – Geoff Hutchison Jun 9 '15 at 15:56

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