9.3. Run path-integral MD with i-PI

The i-PI works in a client-server model. The i-PI provides the server for integrating the replica positions of atoms, while the DeePMD-kit provides a client named dp_ipi that computes the interactions (including energy, forces and virials). The server and client communicate via the Unix domain socket or the Internet socket. Installation instructions for i-PI can be found here. The client can be started by

i-pi input.xml &
dp_ipi water.json

It is noted that multiple instances of the client allow for computing, in parallel, the interactions of multiple replicas of the path-integral MD.

water.json is the parameter file for the client dp_ipi, and an example is provided:

{
  "verbose": false,
  "use_unix": true,
  "port": 31415,
  "host": "localhost",
  "graph_file": "graph.pb",
  "coord_file": "conf.xyz",
  "atom_type": {
    "OW": 0,
    "HW1": 1,
    "HW2": 1
  }
}

The option use_unix is set to true to activate the Unix domain socket, otherwise, the Internet socket is used.

The option port should be the same as that in input.xml:

<port>31415</port>

The option graph_file provides the file name of the frozen model. The model can have either double or single float precision interface.

The dp_ipi gets the atom names from an XYZ file provided by coord_file (meanwhile ignores all coordinates in it) and translates the names to atom types by rules provided by atom_type.