Non-conservative forces

Non-conservative forces are forces that are not calculated as the negative gradient of the potential energy. These are generally faster than forces computed from the potential energy by backpropagation. However, these predictions must be used with care, see https://arxiv.org/abs/2412.11569.

In metatomic models, they are associated with the "non_conservative_forces" key in the model outputs, and must adhere to the following metadata:

Metadata for non-conservative forces output

Metadata	Names	Description
keys	"_"	the keys must have a single dimension named "_", with a single entry set to 0. Non-conservative forces are always a metatensor.torch.TensorMap with a single block.
samples	["system", "atom"]	the samples should be named ["system", "atom"], since non-conservative forces are always per-atom. "system" must range from 0 to the number of systems given as input to the model. "atom" must range between 0 and the number of atoms/particles in the corresponding system. If selected_atoms is provided, then only the selected atoms for each system should be part of the samples.
components	"xyz"	non-conservative forces must have a single component dimension named "xyz", with three entries set to 0, 1, and 2. The non-conservative forces are always 3D vectors, and the order of the components is x, y, z.
properties	"non_conservative_forces"	non-conservative forces must have a single property dimension named "non_conservative_forces", with a single entry set to 0.

The following simulation engines can use the "non_conservative_forces" output, using the non_conservative flag:

LAMMPS

ASE

i-PI

Non-conservative stress

The “non-conservative stress” is a stress tensor that is not calculated using derivatives of the potential energy. This is generally faster than computing the stress from the potential energy by backpropagation. However, these predictions must be used with care, see https://arxiv.org/abs/2412.11569.

In metatomic models, it is associated with the "non_conservative_stress" key in the model outputs, and must adhere to the following metadata:

Metadata for non-conservative stress output

Metadata	Names	Description
keys	"_"	the keys must have a single dimension named "_", with a single entry set to 0. Non-conservative forces are always a metatensor.torch.TensorMap with a single block.
samples	"system"	the samples should contain a single sample named "system" The values must range from 0 to the number of systems given as input to the model.
components	["xyz_1"], ["xyz_2"]	the non-conservative stress must have two components labels with "xyz_1" and "xyz_2" as their respective names, both with three entries set to 0, 1, and 2. The order of the components along both directions is x, y, z.
properties	"non_conservative_stress"	the non-conservative stress must have a single property dimension named "non_conservative_stress", with a single entry set to 0.

The following simulation engines can use the "non_conservative_stress" output, using the non_conservative flag:

LAMMPS

ASE

i-PI