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Running NMR jobs

Generating the input files.

A version of the atm pseudopotential code and a script genpot are available to generate the _AEPS.DAT files. The atm code can also be used to find the diamagnetic shielding contribution of the core states.

Before an nmr run an scf run must be done to obtain a good charge density. A accuracy_diag 1e-12 is probably sufficient. As the nmr routine only works for insulators at the moment use optimze_flags_insulator.

Crystal Method
This calculates the shielding tensors for both crystals and molecules (in the supercell approximation) using the method of PM. The method uses the wavefunctions at points separated by q to obtain a numerical derivative wrt q. Consequently a high degree of accuracy is needed in the wavefunctions and you should set accuracy_diag 1e-14. Results should be stable wrt changing q. nmr_q 0.001 is the default and appears to give stable results.

Eqn3 and Eqn8 Methods
These are formulated for isolated molecules in the unit cell and are several times faster than the crystal method. A accuracy_diag 1e-12 should be ok. The molecule must be centred on the origin of the unit cell.

Comparisons of shieldings calculated with the three methods can be found in PM.


next up previous contents
Next: Calculating the induced current Up: NMR shift Previous: NMR options   Contents
Jonathan Yates 2001-05-10