Hello to the community, I want to tell you that I am investigating the interaction of heavy metal atoms (Pb, Mg, Cr, As, etc.) with magnetite nanoparticles (Fe3O4) so I need a correct potential to represent these nanoparticles. The one that has caught my attention the most is the COMB(Charge-Optimized Many-Body) potential but there is not much literature for the parameters of the force field of Fe+2 and Fe+3 so I ask you if you know of any way, application or paper to obtain these parameters and place them in the “ffield.comb” file.
This seems like a rather unusual combination of components and quite challenging for classical/empirical potentials, too. The first step for this should always be a search of previous research of similar systems to learn what kind of models people have used there.
From my limited experience, I would expect that even ab initio studies of such compounds and systems could be rather demanding (especially for DFT due to the complex electronic structure of Fe ions, but also Cr and other transition metals). This reflects on the parameterization of classical/empirical potentials, since often DFT calculations are the foundation and provide the reference data for such parameterizations.
While parameterization of empirical potentials can be particularly challenging, there is now an alternative path by using machine learning models to train potentials for classical MD codes. This will not eliminate the challenges to get good reference data, and - given the vast variety of ML based schemes to derive potentials - the challenge of choosing a suitable model and then training and validating it.
The procedure should be explained in the papers describing COMB and its sibling COMB3. Those should be referenced in the LAMMPS documentation of those pair styles.
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It is not necessary to use ferrous and ferrous irons since that would complicate the calculation of the parameters a little more, as long as having the O-O, Fe-O and Fe-Fe interaction is enough. Currently, there is no literature on force field parameters for magnetite and heavy metals so I will take your advice to find these parameters using DFT calculations, thank you very much.