This keyword controls the tolerance for accepting convergence of the first-order perturbed wavefunctions in the electronic minimizer during an NMR calculation.
1 × 10-12 when MAGRES_METHOD : crystal
1 × 10-9 when MAGRES_METHOD : molecular
MAGRES_CONV_TOL = 0.00007 eV
To obtain reliable shielding constants, you must ensure a high convergence of the
first-order perturbed wavefunctions. However, there are rare cases where the convergence to within the default accuracy cannot be achieved with
a reasonable number of iterations. In such situations, a warning message will report the minimal residual (largest over the
k-points) achieved by the minimizer, for example:
Calculation of first order wavefunctions not fully converged. Minimum residual = 0.285E-11 eV
In this case, the program does not proceed with the calculation of NMR parameters and the decision is left up to you. If the minimal residual is still reasonably small, as in the example above, it makes sense to run the calculation to completion. To do that, you have to change the MAGRES_CONV_TOL value by setting it in the
.param file to a value larger than that in the warning message.
If MAGRES_CONV_TOL has to be increased by more than one order of magnitude, it is advisable to study the dependence of the NMR
parameters on the value of this computational parameter in order to confirm that the physically relevant results are stable to variations in
CASTEP keyword glossary
CASTEP parameters keywords