8.3. LAMMPS commands

8.3.1. Enable DeePMD-kit plugin (plugin mode)

If you are using the plugin mode, enable DeePMD-kit package in LAMMPS with plugin command:

plugin load path/to/deepmd/lib/libdeepmd_lmp.so

The built-in mode doesn’t need this step.

8.3.2. pair_style deepmd

The DeePMD-kit package provides the pair_style deepmd

pair_style deepmd models ... keyword value ...
  • deepmd = style of this pair_style

  • models = frozen model(s) to compute the interaction. If multiple models are provided, then the model deviation will be computed

  • keyword = out_file or out_freq or fparam or atomic or relative

    out_file value = filename
        filename = The file name for the model deviation output. Default is model_devi.out
    out_freq value = freq
        freq = Frequency for the model deviation output. Default is 100.
    fparam value = parameters
        parameters = one or more frame parameters required for model evaluation.
    atomic = no value is required. 
        If this keyword is set, the model deviation of each atom will be output.
    relative value = level
        level = The level parameter for computing the relative model deviation Examples

pair_style deepmd graph.pb
pair_style deepmd graph.pb fparam 1.2
pair_style deepmd graph_0.pb graph_1.pb graph_2.pb out_file md.out out_freq 10 atomic relative 1.0 Description

Evaluate the interaction of the system by using Deep Potential or Deep Potential Smooth Edition. It is noticed that deep potential is not a “pairwise” interaction, but a multi-body interaction.

This pair style takes the deep potential defined in a model file that usually has the .pb extension. The model can be trained and frozen by package DeePMD-kit.

The model deviation evalulate the consistency of the force predictions from multiple models. By default, only the maximal, minimal and averge model deviations are output. If the key atomic is set, then the model deviation of force prediction of each atom will be output.

By default, the model deviation is output in absolute value. If the keyword relative is set, then the relative model deviation will be output. The relative model deviation of the force on atom i is defined by

Ef_i = -------------
       |f_i| + level

where Df_i is the absolute model deviation of the force on atom i, |f_i| is the norm of the the force and level is provided as the parameter of the keyword relative. Restrictions

  • The deepmd pair style is provided in the USER-DEEPMD package, which is compiled from the DeePMD-kit, visit the DeePMD-kit website for more information.

8.3.3. Compute tensorial properties

The DeePMD-kit package provide the compute deeptensor/atom for computing atomic tensorial properties.

compute ID group-ID deeptensor/atom model_file
  • ID: user-assigned name of the computation

  • group-ID: ID of the group of atoms to compute

  • deeptensor/atom: the style of this compute

  • model_file: the name of the binary model file. Examples

compute         dipole all deeptensor/atom dipole.pb

The result of the compute can be dump to trajctory file by

dump            1 all custom 100 water.dump id type c_dipole[1] c_dipole[2] c_dipole[3] Restrictions

  • The deeptensor/atom compute is provided in the USER-DEEPMD package, which is compiled from the DeePMD-kit, visit the DeePMD-kit website for more information.

8.3.4. Long-range interaction

The reciprocal space part of the long-range interaction can be calculated by LAMMPS command kspace_style. To use it with DeePMD-kit, one writes

pair_style	deepmd graph.pb
kspace_style	pppm 1.0e-5
kspace_modify	gewald 0.45

Please notice that the DeePMD does nothing to the direct space part of the electrostatic interaction, because this part is assumed to be fitted in the DeePMD model (the direct space cut-off is thus the cut-off of the DeePMD model). The splitting parameter gewald is modified by the kspace_modify command.