The CASTEP NMR Options dialog allows you to specify the nuclear quadrupolar moment, Q, used for electric field gradient calculations. The value of the quadrupolar moment depends on the actual isotope. CASTEP makes a suggestion based on the most typical isotope used in solid state NMR experiments. The value of Q affects only the quadrupolar coupling constant, CQ, calculated and printed out by CASTEP. If you find that the wrong value of Q was used you can rescale the generated CQ constant using a different Q value. The list of default values is based on the compilation by Pyykkö (2008).
CASTEP versions before Materials Studio 5.0 used an older compilation by Harris (1996), so some results for quadrupolar coupling constants may have changed in later versions.
NMR in CASTEP is part of the separately licensed module NMR CASTEP. NMR calculations can only be performed if you have purchased this module.
Q moment: Specify the nuclear quadrupolar moment of the element displayed. Change the element type using the dropdown list.
To reset the nuclear quadrupolar moment for the displayed element to the default value, enter 0 for the Q moment.
Reset all Q values to defaults: Sets all nuclear quadrupolar moments for all elements to the default values.
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Properties tab - CASTEP Calculation dialog
Requesting NMR properties