g16-mlips 1.1.1

MLIP plugins for Gaussian16 External (UMA, ORB, MACE, AIMNet2)

g16-mlips

MLIP (Machine Learning Interatomic Potential) plugins for Gaussian 16 External interface.

Four model families are currently supported:

• UMA (fairchem) — default model: uma-s-1p1
• ORB (orb-models) — default model: orb_v3_conservative_omol
• MACE (mace) — default model: MACE-OMOL-0
• AIMNet2 (aimnetcentral) — default model: aimnet2

All backends provide energy, gradient, and analytical Hessian for Gaussian 16. An optional implicit-solvent correction (xTB) is also available via --solvent.

The model server starts automatically and stays resident, so repeated calls during optimization are fast.

Requires Python 3.9 or later.

If you use ORCA, see also: https://github.com/t-0hmura/orca-mlips

Quick Start (Default = UMA)

1. Install PyTorch suitable for your CUDA environment.

pip install torch==2.8.0 --index-url https://download.pytorch.org/whl/cu129

2. Install the package with the UMA profile. If you need ORB/MACE/AIMNet2, use g16-mlips[orb]/g16-mlips[mace]/g16-mlips[aimnet2].

pip install "g16-mlips[uma]"

3. Log in to Hugging Face for UMA model access. (Not required for ORB/MACE/AIMNet2)

huggingface-cli login

UMA model is on Hugging Face Hub. You need to log in once (See https://github.com/facebookresearch/fairchem):

4. Use in a Gaussian input file (nomicro is required). If you use ORB/MACE/AIMNet2, use external="orb"/external="mace"/external="aimnet2". For detailed Gaussian External usage, see https://gaussian.com/external/

%nprocshared=8
%mem=32GB
%chk=water_ext.chk
#p external="uma" opt(nomicro)

Water external UMA example

0 1
O  0.000000  0.000000  0.000000
H  0.758602  0.000000  0.504284
H -0.758602  0.000000  0.504284

Other backends:

#p external="orb" opt(nomicro)
#p external="mace" opt(nomicro)
#p external="aimnet2" opt(nomicro)

Important: For Gaussian External geometry optimization, always include nomicro in opt(...). Without it, Gaussian uses micro-iterations that rely on an internal gradient routine, which is incompatible with the external interface. ONIOM is supported with both ActiveAtoms and AllAtoms. With AllAtoms, Gaussian passes IAn=0 MM point-charge rows to the plugin. By default these IAn=0 rows are excluded from MLIP evaluation and returned as zero force/Hessian blocks.

For ONIOM point-charge embedding correction via xTB:

#p oniom(external=("uma --embedcharge",AllAtoms):amber=softfirst) opt(nomicro)

--embedcharge adds an xTB point-charge embedding correction using ONIOM MM charges. When igrd=2, it also returns MM point-charge force/Hessian terms from the embedding correction.

Analytical Hessian (optional)

Optimization and IRC can run without providing an initial Hessian — Gaussian builds one internally using estimated force constants. Providing an MLIP analytical Hessian via freq + readfc improves convergence, especially for TS searches.

Gaussian freq (with external=...) is the only job type that requests the plugin's analytical Hessian directly.

Frequency calculation

%nprocshared=8
%mem=32GB
%chk=cla_ext.chk
#p external="uma" freq

CLA freq UMA

0 1
...

Gaussian sends igrd=2 and stores the result in the .chk file.

Implicit Solvent Correction (xTB)

You can use an implicit-solvent correction via xTB. To use it, install xTB and pass the --solvent option to external.

Install xTB in your conda environment (or built from source):

conda install xtb

Use --solvent <name> in external="..." (examples: water, thf):

#p external="uma --solvent water" opt(nomicro)
#p external="uma --solvent thf" freq

For details, see SOLVENT_EFFECTS.md.

This implementation follows the solvent-correction approach described in: Zhang, C., Leforestier, B., Besnard, C., & Mazet, C. (2025). Pd-catalyzed regiodivergent arylation of cyclic allylboronates. Chemical Science, 16, 22656-22665. https://doi.org/10.1039/d5sc07577g

If citing this correction in a paper, you can use the following: Implicit solvent effects were accounted for by integrating the ALPB [or CPCM-X] solvation model from the xtb package as an additional correction to UMA-generated energies, gradients, and Hessians.

Note: --solvent-model cpcmx (CPCM-X) requires xTB built from source with -DWITH_CPCMX=ON. The conda-forge xtb package does not include CPCM-X support. See SOLVENT_EFFECTS.md for build instructions.

Using the analytical Hessian in optimization jobs

To use the MLIP analytical Hessian in opt/irc, read the Hessian from an existing checkpoint using Gaussian %oldchk + readfc.

%nprocshared=8
%mem=32GB
%chk=cla_ext.chk
%oldchk=cla_ext.chk

#p external="uma" opt(readfc,nomicro)

CLA opt UMA

0 1
...

readfc reads the force constants from %oldchk. This applies to opt and irc runs. Note that freq is the only job type that requests the analytical Hessian (igrd=2) from the plugin. opt and irc themselves never request it directly.

Installing Model Families

pip install "g16-mlips[uma]"         # UMA (default)
pip install "g16-mlips[orb]"         # ORB
pip install "g16-mlips[mace]"        # MACE
pip install "g16-mlips[orb,mace]"    # ORB + MACE
pip install "g16-mlips[aimnet2]"     # AIMNet2
pip install "g16-mlips[orb,mace,aimnet2]"  # ORB + MACE + AIMNet2
pip install g16-mlips                # core only

Note: UMA and MACE have a dependency conflict (e3nn). Use separate environments.

Local install:

git clone https://github.com/t-0hmura/g16-mlips.git
cd g16-mlips
pip install ".[uma]"

Model download notes:

• UMA: Hosted on Hugging Face Hub. Run huggingface-cli login once.
• ORB / MACE / AIMNet2: Downloaded automatically on first use.

Upstream Model Sources

• UMA / FAIR-Chem: https://github.com/facebookresearch/fairchem
• ORB / orb-models: https://github.com/orbital-materials/orb-models
• MACE: https://github.com/ACEsuit/mace
• AIMNet2: https://github.com/isayevlab/aimnetcentral

Advanced Options

See OPTIONS.md for backend-specific tuning parameters. For solvent correction options, see SOLVENT_EFFECTS.md.

Command aliases:

• Short: uma, orb, mace, aimnet2
• Prefixed: g16-mlips-uma, g16-mlips-orb, g16-mlips-mace, g16-mlips-aimnet2

Troubleshooting

• external="uma" runs the wrong plugin — Use external="g16-mlips-uma" to avoid alias conflicts.
• external="aimnet2" runs the wrong plugin — Use external="g16-mlips-aimnet2" to avoid alias conflicts.
• uma command not found — Activate the conda environment where the package is installed.
• UMA model download fails (401/403) — Run huggingface-cli login. Some models require access approval on Hugging Face.
• Works interactively but fails in PBS jobs — Use absolute path from which uma in the Gaussian input.

Citation

If you use this package, please cite:

@software{ohmura2026g16mlips,
  author       = {Ohmura, Takuto},
  title        = {g16-mlips},
  year         = {2026},
  month        = {2},
  version      = {1.1.0},
  url          = {https://github.com/t-0hmura/g16-mlips},
  license      = {MIT},
  doi          = {10.5281/zenodo.18717988}
}

References

• Gaussian External interface (official): https://gaussian.com/external/
• Gaussian External: $g16root/g16/doc/extern.txt, $g16root/g16/doc/extgau