I’ve recently tried to use GULP to find the phonon frequencies of a supercell model I have. The connectivity of all atoms are specified explicitly in the input file, and they have periodic boundary conditions. The .disp output file has all phonons at all k points with a frequency of 0 and the .gout output file has the following error repeated:
**** Warning - inter/intra/both directive given on potential line ****
**** but the molecule directive is currently inactive ****
Do you know what is going wrong and what I should do?
Many thanks,
In GULP, the use of bonding-based cutoffs (i.e. molecular mechanics) for potentials, such as bond, intra, inter, x12, x13, o14, molmec, is activated when one of the molecule keywords is specified (i.e. molecule, molq, molmec). Hence the reason why your energy, forces and frequencies are zero is almost certainly because your potentials are specified with one of the bonding related cutoffs, but the molecule keyword is missing and so no potentials are found to act on your system. The solution is to add the appropriate keyword from one of the three above (depending on what you want to do with any charges present) and as you’re manually specifying the connectivity (rather than letting GULP find it automatically) then you can add the keyword “noautobond” to stop GULP from finding the bonds.
Hope that clarifies things.
Regards,
Julian
I used the noautobond and molq keywords as advised and now my output gives me the phonon frequencies I was after.
Thank you very much for your help and for answering my query so quickly!