Strontium titanate potential function

What does the potential function in the image look like when written in lammps format?

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What does that mean? A potential function is a potential function. They sometimes may look different because people use different names for the constants or different definitions (e.g. whether sigma in Lennard-Jones is the radius for epsilon==0 or MIN(epsilon)), but that can be easily resolved by comparing the descriptions of the functions.

Everything that LAMMPS offers is documented, and all pairwise potentials for which no explicit functional form exists, one can tabulate it or try to fit it to a different but similar functional form.