XFF

XFF · parameter server

XtalPi Force Field (XFF)

XFF is an AMBER-compatible force field for drug-like molecules. It achieves outstanding performance in reproducing QM energies and geometries, as well as free energy perturbation (FEP) accuracy.

Register to generate Command line tool

How it works

From molecule to parameter files

  1. Provide a molecule

    Upload a mol or sdf file (V2000 and V3000 are both supported), or a mol2 file that already carries its charges.

  2. Add partial charges

    Upload the charges as a separate file, or use a mol2 file that already carries them. Supported charge formats.

  3. Download the parameters

    Choose Amber, CHARMM or GROMACS and get the parameter and topology files in one archive.

Partial charges

Bring your own charges

The recommended partial charge model for XFF is RESP. You can obtain it with AmberTools and Gaussian, and upload it as a separate charge file.

mol and sdf files carry no partial charges, so they always need a charge file. Without one every charge in the output would be zero, and the server asks for the file instead of running.

  • mol2 with charges

    Example

    For example, a mol2 file obtained with antechamber using the -c bcc option.

  • Single-column file

    Example

    One partial charge per line, in atom order.

    -0.01
0.02
-0.03
...

  • Two-column file

    Example

    Atom index (starting from 1), then the partial charge.

    1 -0.01
2 0.02
3 -0.03
...

Command line

Download GENXFF

Prefer to run it locally? GENXFF is also distributed as a command line tool. Write a small config file, point it at your molecule and charge files, and it writes the same parameter files.

  • Linux x86 only
  • Licence agreement required
Sign in to download Read the user manual

By downloading GENXFF or getting XFF parameters online, you agree to our license agreement. 

# generate parameters from a config file
$ genxff --config example.config

# dump the complete config template
$ genxff --dump_config template.config

Release history

Details for different versions of XFF

  1. XFF 1.1 Default

    Fix the torsion parameters related to the following structures:

    • Piperazin-2-one
    • Protonated 3-amino-1H-isoindole (cyclic amidinium)
    • Chloro-substituted dihydrofuropyridine, with the vinyl chloride fragment highlighted
  2. XFF 1.0

    The version used in the XFF manuscript.

Note: this deployment runs a genxff build with the XFF 3.0.1.8 parameters compiled in, so 1.1 is the version it produces. Producing 1.0 needs its parameter file installed on the server.

References

  1. Bai Xue, Qingyi Yang, Qiaochu Zhang, Xiao Wan, Dong Fang, Xiaolu Lin, Guangxu Sun, Gianpaolo Gobbo, Fenglei Cao, Alan M. Mathiowetz, Benjamin J. Burke, Robert A. Kumpf, Brajesh K. Rai, Geoffrey P. F. Wood, Frank C. Pickard IV, Junmei Wang, Peiyu Zhang, Jian Ma, Yide Alan Jiang, Shuhao Wen, Xinjun Hou, Junjie Zou, and Mingjun Yang. Journal of Chemical Theory and Computation 2024, 20 (2), 799–818.

    Read the paper

Contact us: xff@xtalpi.com

About XtalPi

Visit xtalpi.com

XtalPi (XtalPi Holdings Limited, 2228.HK) is an AI for Science company building infrastructure for autonomous scientific discovery. Grounded in quantum physics and powered by AI and robotics, XtalPi connects Agentic AI, Scientific AI, and Physical AI to bring scientific reasoning into the laboratory and create a continuous loop of prediction, experimentation, and learning.

By integrating scientific intelligence with large-scale robotic experimentation, XtalPi aims to turn AI into scalable scientific productivity—accelerating the discovery of innovative medicines, new-energy technologies, advanced materials, and chemicals, and shortening the path from scientific insight to real-world outcomes.