Tersoff alloy potential

Dear Lammps users!

In tersoff paper PRB 39, 5566 1989 parameters for SiC potential and mixing rules for cross 2-body terms are given. I’m wondering how cross 3-body terms are generated. In SiC.tersoff potential file parameters c, d, h are equal for CCC, CSiSi, CSiC, CCSi entries. They are also equal to each other for remaining 4 entries. Could you please tell what is the reason behind it? Thank you!

please have a look at the documentation for the tersoff pair style which explains what LAMMPS is reading and using from the potential file.
all potential files distributed with LAMMPS have a reference where the parameters are taken from and name the person that contributed the potential file.
you have to look up the details of the respective parameterizations in those publications and - if needed - contact the person that contributed the potential.

what you are asking is not really a question about LAMMPS and thus - strictly speaking - not a topic for this mailing list. LAMMPS is just the simulation engine, it doesn’t care why parameters are chosen how. it takes them and runs simulations with whatever you throw at it, for as long as it follows the correct syntax.