Thank you for your answer to my last question on bond lengths. I’m now attempting to fit a Buckingham potential to NiO using INS phonon frequencies. I have attached my input file and the initial/final observables.
My question is: at the X and L points, GULP predicts the LA band crosses the TO band, which doesn’t agree with the data. Is this GULP’s way of telling me that the Buckingham potential is insufficient, or have I made a mistake entering the frequencies in my input file?
Hi Connor,
I haven’t had chance to check your run yet, but I suspect that this is the usual gotcha for F centred cells (or other non-primitive systems). Often people talk about the Brillouin zone of the cubic (centred) system, but by default the k points in GULP refer to the primitive cell. If you add the keyword “kfull” this will switch the k points to the cubic setting and so I suspect this may fix your issue.
Regards,
Julian