the sequence of parameters in REBO potential

Dear LAMMPS users,

In REBO potential for carbon-hydrogen, there is a Pij term which is a bicubic interpolation depends on the number of neighbor atoms (x=C, y=H). But I’m not sure about the sequence of the coefficients implemented in the potential file?

For example in a simple unit cubic square case where the x and y vary from 0 to 1 (shown below), is the aij implemented by rows or by columns?

Thank you so much for your help!



I suggest you look in the code to see how it interprets

the values it reads from the potential file.