Checking the NMR checkbox on the Properties tab displays options for calculating shielding tensors and electric field gradients.
NMR in CASTEP is part of the separately licensed module NMR CASTEP. NMR calculations can only be performed if you have purchased this module.
Calculate: Specify the properties you wish to calculate. Available options are:
The calculation of the shielding tensor is not implemented for metallic systems. If the system is a metal you should choose EFG from the Calculate dropdown list.
The shielding tensor is ill-defined for spin-polarized calculations, so when an NMR calculation is requested for a spin-polarized system CASTEP will calculate only electric field gradients.
System type: Specify whether the system used in the calculation is a Crystal or a Molecule.
Calculations in the Molecule mode can only be performed for systems with P1 symmetry. If your crystal representing molecule in the box has symmetry other than P1, you will be prompted to convert the crystal symmetry to P1 before you can continue.
Max. steps: Specify the maximum number of conjugate gradient steps taken for each electronic band in the electronic minimizer during an NMR calculation of the first-order perturbed wavefunctions. Default = 250.
More...: Provides access to the CASTEP NMR Options dialog, which allows you to specify the nuclear quadrupolar moment for each element.
Calculation of the NMR parameters requires higher accuracy for the wavefunctions than total energy or geometry optimization calculations. This affects how you choose the Energy cutoff quality parameter on the Electronic tab, even choosing Ultra-fine may not be sufficient to obtain high quality NMR parameters. Therefore, it is advisable to study the convergence of the results as the Energy cutoff parameter is increased. Generally, setting the cutoff to between 270 and 400 eV should produce convergence of the shielding constant to about 1 ppm, but in some cases, the cutoff has to be increased up to 550 eV.
|Menu||Modules | CASTEP | Calculation | Properties | NMR|
|Toolbar||| Calculation | Properties | NMR|
Properties tab - CASTEP Calculation dialog
Requesting NMR properties
Calculating NMR shielding tensors using pseudopotentials