Reax vs reax/c and hbnewflag

Hello,

I have been running a CHO system in reax, and I realized that there was a difference between the reax and reax/c energies. Upon further investigation, I realized that for reax and reax/c to return the same energies, the binary flag “hbnewflag” in reax has to be set to 1. This corresponds to the new H-bond function style (as opposed to the old), according to the LAMMPS documentation. Without using the new style, the H-bonding energies are significantly different. For example, a system I was running in reax had an H-bonding energy of -3359 kcal/mol with hbnewflag = 0, and an H-bonding energy of -4948 kcal/mol with hbnewflag = 1. The latter was consistent with the reax/c results. The former was not.

Does anyone know why these energies are so different, and what these two “H-bond function styles” correspond to? I have been perusing the documentation, and haven’t found anything. Most importantly, which one is more correct?

Thanks,

-Keith

Hi Keith,

The difference is the exponent of the sinus of the angle between three atoms in a hydrogen bond. Old style has sin^8 and new one has sin^4.
The value of the flag depends on the potential file you use. Settings for potential files bundled with LAMMPS can be found in the file README.reax in $LAMMPSDIR/potentials directory. If you use a different parametrization, you’ll have to ask its authors for a correct value of the flag.

Michal