I am trying to fit an interatomic potential of the Buckingham form for CsCl, the interactions include Cs-Cl and Cl-Cl, and none of them are known. It seems impossible to fit 2 interactions from one crystal structure, because GULP reminds me that the number of variables exceeds the number of observables. However, I was inspired by a paper (J. Phys. Chem. B 2018, 122, 2940−2948), in which 5 pairs of fluoride interactions were fitted from 4 crystal structures. The original content of the paper is shown in the picture. I am a new user in GULP, and I am wondering that could you give me some advice on how to fit interactions parameters from a series of crystal structures, just as the paper did?
Any advice on this would be very helpful.
Most of the fitting advice is captured in the GULP fitting paper in Phil. Mag. B that’s listed in the references in the code. This should cover most things. Note there can be more than 1 observable per crystal structure if the symmetry is low or if you give elastic constants and other properties. It’s only for high symmetry cases like CsCl where one lattice parameter is all you need to completely specify the structure that there is so little data in the structure alone.
Thank you for your reply, this will help a lot!