lithium niobate

Hi Lammps users,

I’m trying to use a classical potential for lithium of niobate . I found in the literature two reference in regard the creation of the potential: 1). H Donnerberg, Phys. Rev. B, vol. 40, p. 11909, 1989, and 2). R A Jackson, J. Phys.: Condensed Matter, vol. 17 p. 837, 2005 .
unfortunately i’m stuck at defining the pair interactions in lammps .

According to the article there are three pair ion-ion interaction between (O2- O2-), (Nb5+ -O2-), and (Li±O2-) all these interactions
are Buckingham potentials, thus if “type 1 is O” , “type 2 is Nb” and “type 3 is Li” , then i would use :

pair_style buck
pair_coeff 1 1 args (interaction O2- O2-)
pair_coeff 2 1 args (interaction Nb5+ O2-)
pair_coeff 3 1 args (interaction Li+ O2-)

Then it define a Shell Model potential interaction (which i belive its not yet implemented in lammps) , and There is also a threebody bond-bending (O - Nb - O) term used to model the directional character of covalent bonds (which i have no idea how to define in lammps).

Can someone please tell me how to define the threebody-Bond-bending term in lammps, if the functional form is “bond_style harmonic?”

Thank you
Oscar G.

3-body is an angle style in LAMMPS lingo.