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The input files required to run a field theoretic simulation (FTS) are closely analogous to those required an SCFT calculation for a periodic system. The pscf_pc or pscf_pg program must be invoked with command line parameters that specify the names of a parameter file and a command file. The main difference in the command file is simply that a SIMULATE command is used to run a stochastic simulation, rather than the ITERATE or SWEEP command used to run an SCFT calculation or an SCFT parameter sweep.
FTS Example
For example, suppose that we want to use pscf_pg to run a GPU-accelerated BD simulation of 30,000 BD steps in a 3D domain, using a parameter file named param and a command file named command. To do so, we might invoke the pscf_pg executable as
We assume that the parameter file "param" contains a BdSimulator block that specifies appropriate choices of algorithms and parameters for a BD step algorithm, a compressor algorithm, and any desired analyzers.
Before begininng a FTS, we must read in an initial field configuration from a field file. Field files used to initialize a FTS must be input and output in the r-grid file format, which gives values for the w fields on the nodes of a grid, and does not impose any space group symmetry. This is done using the READ_W_GRID command, as shown in the following example.
Unlike field files for SCFT, field files used for FTS generally do not contain a line in the field file header that declare a space group. This is because the randomly fluctuating fields characteristic of a FTS are generally not exactly invariant under any nontrivial space group symmetry operations.
Suppose that we run a simulation from a directory that contains subdirectories named 'in' and 'out', in which directory 'in' contains an initial field file named 'in/w.rf', while all output files are written to subdirectory named 'out'. A simple command file for such a simulation might look something like the following:
In this example, the READ_W_RGRID command reads in a specified w-field file named in/w.rf. The SIMULATE command actually runs the simulation. After the simulation is complete, the WRITE_W_RGRID and WRITE_C_RGRID commands writes the final w and and c field configurations to files within the out/ directory. The WRITE_TIMERS command writes a report about the amount of time taken by various computational operations to a file named 'out/timers'.
The most important new command in this example is the SIMULATE command. This command runs a simulation of a specified number of BD or MC steps, and takes the number of steps as a parameter. In this example, the SIMULATE command thus runs a simulation of 30000 steps. The type of simulation that is performed (i.e., BD vs. MC) and the choice of algorithms and parameter values used in that simulation are all specified in the parameter file, which is always read and processed before the command file. A FTS simulation must thus be initialized by a parameter file that contains either a BdSimulation block for a BD simulation, or an McSimulation block for an MC simulation.
Commands for FTS
The commands that can be used for SCFT calculations performed with pscf_pc have already been listed here here. Most of these commands can also be used in a command file for pscf_pg. Specifically, commands for reading and writing field files such as READ_W_RGRID and WRITE_W_RGRID can be used in either context, as can the timer commands and many of the utility commands for manipulating field files.
The following table lists a set of commands that are accepted by either pscf_pc or and pscf_pg that are only meaningful in the context of an FTS simulation, and that were thus not listed among the commands that can be used for SCFT calculations.
| command | parameter(s) | action |
| SIMULATE | nStep | Perform a field-theoretic simulation of nStep steps. |
| ANALYZE | min, max, readerName, filename | Postprocess a field trajectory output by looping over frames of a field trajectory file output by a previous simulation. Analyze frames with frame numbers min to max from file filename, using a TrajectoryReader object that is an instance of class readerName. |
| COMPRESS | Iteratively adjust the Lagrange multiplier pressure field component of the current w fields so as to satisfy the incompressibility constraint (i.e., the partial saddle point condition). |
SIMULATE : THE SIMULATE command performs a field-theoretic MC or BD simulation of a specified number of steps. The number nStep of BD steps or attempted MC moves is given as the only command parameter. The associated parameter file (which is read before the command file) must contain a BdSimulator or McSimulator blocks that contains all of the elements necessary to run a simulation. Field trajectories may be written to file by including a TrajectoryWriter among the analyzers listed in the AnalyzerManager subblock of the BdSimulator or McSimulator block.
ANALYZE : THE ANALYZE command reads and analyzes a field trajectory file with the name given by the "filename" parameter that was written by a previous field-theoretic simulation. This postprocess analysis procedure is discussed in more detail elsewhere.
Analysis operations listed in the parameter file are performed only for frames of the trajectory file with frame index values that lie between min and max (inclusive). Setting the max parameter to any value greater than or equal to the number of frames in the trajectory file, while min is less than the number of frames in the file, will cause the program to read and process frames until the end of file is reached.
The trajectory file with a name given by the "filename" parameter is read and parsed by an instance of a subclass of the TrajectoryReader class with a name specified by the "readerName" parameter. Currently, the readerName parameter should always be set to "TrajectoryReader", which selects a default reader algorithm that can read the file format that is written by the "TrajectoryWriter" analyzer class.
The parameter file used to initialize a postprocessing operation must contain a BdSimulator or McSimulator block with an AnalyzerManager subblock that specifies what analysis operations should be applied to the chosen frames of the trajectory file. Every Analyzer in the AnalyzerManager block is applied to frames with frame indices between the values specified by the min and max command parameters when the frame index is a multiple of the interval parameter of the Analyzer.
COMPRESS : The COMPRESS command applies the compressor algorithm that is specified in the parameter file to the current w-fields. The compressor iteratively adjusts the pressure-like field component \( W_{+}({\bf r}) \) so as to satisfy the mean-field incompressibility constraint to within a tolerance that is specified in the parameter file, without changing any of the other w-field components.
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