Socket-Communication

For calculations that heavily rely on file-IO and situations where initialization times are not negligible, socket communcation is often preferable and might lead to a significant reduction of wallclock time. The i-PI protocol [15] is among the most famous options in this regard and supported by Fortnet.

Below, compiling and running Fortnet with support for socket communication is outlined.

Note

Note: At this time, only communication with ASE or i-PI has been tested. In general, however, other software which correctly implements the i-PI protocol should be supported.

Compiling with Socket Support

To enable socket-communication in Fortnet the WITH_SOCKETS flag in the configuration file config.cmake must be set to TRUE, before starting the compilation process. Equivalently, this configuration step is also possible directly from the command line, e.g. invoke:

FC=mpifort CC=gcc cmake -DTOOLCHAIN=gnu -DWITH_SOCKETS=1 -B _build .

Providing the Input for Fortnet

[Input: recipes/interfaces/sockets/input/]

To establish a connection via socket communication, Fortnet is called with the appropriate Socket{} driver option, e.g.:

Driver = Socket {
  File = 'fortnet'
  Protocol = i-PI {
    # Non-periodic water molecule (H2O)
    Periodic = No
    AtomicNumbers = 8 1 1
  }
  MaxSteps = 1000
  Verbosity = 0
}

It instructs Fortnet to read geometry driving commands via a named temporary communication file (stored in /tmp/). The code is asked to perform up to MaxSteps = 1000 geometry steps under control of the external driver. For codes that support the EXIT command in the protocol, Fortnet may be told to continue running until told to stop by using:

MaxSteps = -1

For initialization purposes, rudimentary geometry specifications, like the (atomic) number of atoms and boundary conditions, must be provided. Make sure that the atomic numbers are given in the same order as for the geometries that will be send via the socket connection later on.

Additionally, a network initialization file (NetstatFile) must be specified and read. Operating in socket mode always requires force analysis, which is assumed (and overwritten) even if not requested by the user:

Data {
  NetstatFile = 'fortnet.hdf5'
}

Options {
  ReadNetStats = Yes
  Mode = 'predict'
}

Analysis {
  Forces = Analytical {}
}

For the full input file assembled from the code snippets shown here, please consult the archive, whose location is stated at the begin of this section.