splining EAM+ZBL

I think that the first term of EAM (density function) will be influenced by
spline ZBL to the pairwise portion of EAM. So, modifying the form of density
function should be taken into account when we combine the ZBL with EAM. But I'm
not confirm that. Does someone have comments.

I don't think the idea to replace the tabulation of EAM that Steve mentioned
is a good method, though many people might have done EAM-ZBL hybrid in that

i disagree.

way. My concern is that spline the pair potential actually can avoid
overlap, but since the force is calculated by the derivative of potential
and considering that the potential formulas of EAM and ZBL are different,
the force calculated with the newly tabulated EAM would be different from
the force calculated with ZBL by the same value of potential and also
different from the real circumstance we expect.

To fit a new formula around the overlap point, and implement it in the
source code of lammps seems more reasonable for me.

However, I'm also just new to the potential discipline, please correct me if
there is anything wrong with me.

i don't know if there is anything wrong with you (i hope not), but
your concern is not valid.
when you tabulate a potential and then interpolate it with a spline
function, you will get a smooth interpolation that is a continuous
function with a continuous derivative function as well. this is by
construction. of course there can be artifacts if there is a
significant change in the potential at the transition point, but for
as long as you shift one of the potentials to have the same value as
the other (like steve mentioned), this will be minimal and should not
be a big concern. you should make an experiment and plot the resulting
function yourself. LAMMPS can help you to do that experiment without
having to write code yourself through using the pair_write command,
that writes out pairwise potentials, and the pair table style that
supports reading a tabulated potential and resplining them to
different grids.