ReaxFF input files
This directory documents the input files used by ReaxFF.
ReaxFF input files can be divided into mandatory files, which are required for any run, and optional files, which are only needed for specific simulation modes or advanced workflows such as force field optimization.
This reference focuses on the file formats and their roles, independent of ReaxKit-specific tooling.
Overview of ReaxFF input files
The table below summarizes all commonly used ReaxFF input files, their role, and whether they are required.
Table 1 — ReaxFF input files
| File name | Category | Short description |
|---|---|---|
geo |
Mandatory | System geometry |
ffield |
Mandatory | Force field parameters |
control |
Mandatory | Run-control switches |
exe |
Mandatory | Execution script used to launch ReaxFF |
models.in |
Optional | Geometry file locations |
tregime.in |
Optional | Temperature regime definition |
vregime.in |
Optional | Volume / cell-parameter regime definition |
eregime.in |
Optional | Electric field definition |
iopt |
Optional | Toggle between normal run and force field optimization |
addmol.bgf |
Optional | Molecular fragment definition for on-the-fly insertion |
charges |
Optional | Fixed atomic charges |
vels |
Optional | MD restart file |
trainset.in |
Force field optimization | Training set / cost-function definition |
params |
Force field optimization | Optimizable force field parameters |
koppel2 |
Force field optimization | Linked force field parameters |
File categories
Mandatory files
These files must be present for any ReaxFF run:
- geo
- ffield
- control
- exe
Without these files, ReaxFF will not start.
Optional simulation-control files
These files enable advanced simulation protocols:
- tregime.in — temperature control
- vregime.in — strain and volume control
- eregime.in — external electric fields
- addmol.bgf — molecule insertion (GCMD-style simulations)
- charges — fixed-charge simulations
- vels — MD restarts
- models.in — geometry management
Force field optimization files
These files are only required when optimizing ReaxFF force fields:
- iopt
- trainset.in
- params
- koppel2
Together, they define: - what data is fitted, - which parameters are optimized, - how parameters are linked, - and how the optimization is executed.
How to use this reference
Each file listed above has a dedicated Markdown page in this directory describing: - its purpose, - file format, - examples, - and common usage patterns.
Start with the mandatory files, then explore optional and optimization-related files as needed.