Looking for the W99 force field

Hi ,
I want to simulate the collision of hydrocarbon with only physical changes.So the AIREBO forcite field adn Reaxff can not be used. And the dreiding force field is too old and inaccurate for hydrocarbon. I want to know where can i find the isoPAHAP or W99 force field to simulate in lammps.

Hi ,
I want to simulate the collision of hydrocarbon with only physical
changes.So the AIREBO forcite field adn Reaxff can not be used.

that is incorrect. you *can* use both of them. they will just be more
expensive to compute than simpler models.

And the dreiding force field is too old and inaccurate for hydrocarbon.

I want to know where can i find the isoPAHAP

you already have received an authoritative answer for isoPAHAP. why do
you ask again as if this is the first time?

or W99 force field to simulate in lammps.

the procedure is always the same for all kinds of potentials:
1) study the literature to find the publication(s) describing the
force field, how to assign parameters and how it was validated
2) compare the functional form of the potential to the available pair
styles in LAMMPS and see, if there is a match.
2a) if the potential is pairwise additive, you may also try out using
pair style table.
3) run tests to reproduce the reference data provided in the published
literature.

axel.