MTP - Moment Tensor Potential¶

Description¶

The Moment Tensor Potential writes the energy of atom \(i\) as

\[ E_i = c_{\alpha_i} + \sum_{k} \xi_k \, B_k(\mathfrak{n}_i) \]

where \(c_{\alpha_i}\) is a per-species constant and the \(B_k\) are scalar contractions of the moment tensors of the neighborhood \(\mathfrak{n}_i\) of atom \(i\). The linear coefficients \(\xi_k\) are shared by all species; species dependence enters through the radial functions. The potential is read from a single .almtp file.

Build

Configure exaStamp with -DEXASTAMP_MLIP_MTP_BUILD=ON. MTP has no external dependency.

Operators¶

mtp_init reads the potential file once, in init_parameters, and raises rcut_max to the MTP cutoff. mtp_force computes energies, forces and the virial in compute_force.

Syntax

init_parameters:
  - species
  - mtp_init:
      parameters:
        mtp_file: <string>

compute_force:
  - mtp_force

Parameters

parameters.mtp_file:  string, required   # MTP potential file (.almtp).

mtp_init needs the species operator to have run before it, so list species first in init_parameters.

Usage example

includes:
  - config_update_symmetric_forces.msp

species:
  - Cu: { mass: 63.546 Da , z: 29 , charge: 0.0 e- }

init_parameters:
  - species
  - mtp_init:
      parameters:
        mtp_file: "pot.almtp"

compute_force:
  - mtp_force

A complete example is in exaStamp/data/regression_new/mliaps/mtp/exastamp_example/Cu_mtp.msp.

Descriptors¶

MTP descriptors, their derivatives and the global fitting matrix are computed by compute_descriptor_mtp, compute_descriptor_mtp_global and write_descriptor_mtp_global. See Descriptors.