Dear LAMMPS community,
I am a LAMMPS beginner and try to implement the potential for CaWO4 from [A. Senyshyn et al., Phys. Rev. B 70 (2004) 214306, DOI:10.1103/PhysRevB.70.214306] in my simulation. The authors of this paper use a combination of Coulomb, Buckingham, Morse, and Three-body potential to model the CaWO4 potential.
Using LAMMPS’ pair_style hybrid/overlay, I was able to combine pair_style coul/long (+ kspace_style ewald), pair_style buck, and pair_style morse; using the values from [Senyshyn2004, tab.1] to set the pair_coeff.
Now I am stumbling how to “translate” the values of k_three/2 and theta_0 given for O-W-O from the paper to LAMMPS’ pair_style nb3b/harmonic:
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Do I understand the LAMMPS manual correctly, that I have to give values for all permutations of O,W? As the paper gives only parameters for O-W-O, I have to set the parameters for all other permutations to zero?
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Would I have to permute over all three atom species of CaWO4 or only over W,O as the three-body potential is only relevant for O-W-O?
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The manual state that if the non-centre atoms are equal, k_three and theta_0 are irrelevant. Would this mean that in my case, both non-centre atoms are O, no parameter at all is relevant? I doubt this, because otherwise I think the three-body potential would not be needed in [Senyshyn2004].
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Lastly not strictly a LAMMPS questions, but maybe there is some community knowledge how to deal with the following: For pair_style nb3b/harmonic, I have also to provide a cut-off value, but [Senyshyn2004] does not report a cut-off for their three-body potential. Is it possible to calculate or estimate or guess an appropriate value?
Thank you very much for any help, comments, or suggestions!