Input Files

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Types of input file

To perform either a SCFT of PS-FTS calculation, a PSCF program must generally read three different types of input file:

• a parameter file
• a command file
• a field file

All PSCF programs use similar formats for parameter and command files. Several different formats may be used for field files.

Parameter file

When any PSCF program is executed, the parameter file is processed first. The name of the parameter file is specified as command line argument when a PSCF program is invoked, as the parameter of the required "-p" command line option.

The parameter file defines the physical parameters of the problem of interest and initializes the state of the program. This file contains physical information about chemical structures (e.g., monomer properties and block polymer structures), composition (the volume fraction or chemical potential of each species in a mixture), interactions among constituents (Flory-Huggins chi parameters), information about the spatial domain of interest (e.g., the Bravais lattice type of a periodic structure), a description of a spatial discretization for that domain, and a variety of other algorithmic parameters.

An example of a parameter file for an SCFT calculation performed using the pscf_pc or pscf_pg program is shown and discussed in later manual page, here .

Command file

The command file is always processed immediately after the parameter file, and controls program flow after initialization. A command file contains a list of commands that are interpreted and executed in the order listed. Each line of a command file starts with a capitalized command name, which may be followed by one or more arguments. The name of the command file that controls a calculation is always specified as a required command line argument, as the parameter of the "-c" command line option.

An example of a command file for an SCFT calculation performed using the pscf_pc or pscf_pg program is shown and discussed here.

Field files

A field file contains a description of a set of fields (i.e., functions of position) that are associated with different monomer types. The most important types of field are chemical potential fields associated with different monomer types, sometimes referred to as "w-fields", and fields that represent mononer concentration or volume fraction, sometimes referred to as "c-fields".

Some commands in a command file perform operations that read or write field files. For example, the first command in a command file for a SCFT calculation is usually a command to read an initial guess for the monomer chemical potential fields from an input field file. The last commands in such a command file are often commands that write the converged chemical potential and monomer concentration fields to output files. The names of these input and output field files are specified within the command file as command parameters.

Several different field file formats are used by PSCF programs. For each program, the same file format or set of file formats are used for both w-fields and c-cfields. The pscf_pc and pscf_pg programs use identical sets of field file formats, while pscf_1d uses a somewhat different format.

The pscf_pc and pscf_pg programs can use either "basis" or "r-grid" format for field files. The "basis" format uses a symmetry-adapted Fourier series expansion of each field that is designed to represent periodic fields that are invariant under all symmetry operations of a specific space group that is declared in the parameter file. The "r-grid" file format instead contains values of fields on nodes of a regular computational mesh, and does not require or assume the existence of any space group symmetry.

The names of many commands used by the pscf_pc and pscf_pg programs to read or write field files all end with a suffix "BASIS" or "RGRID", respectively, to specify which of these two file format should be used. For example, the command for these programs that reads an initial set of w-fields in basis format is named READ_W_BASIS, while the command that outputs the current set of c-fields in r-grid format is named WRITE_C_RGRID. Files containing chemical potential fields (w-fields) used for SCFT calculations for periodic structures of known space group symmetry are often both input and output in basis format, since this format automatically imposes symmetry under operations of a space group symmetry declared by the user. Files containing w-fields used for PS-FTS simulations are instead normally input and output in r-grid format, since stochastic field theoretic simulations do not exactly preserve any space group symmetry. Monomer concentration fields may be output in either format, but are often output in r-grid format for purposes of visualization.

The pscf_1d command uses a single field file format for both w- and c- fields. The data section of this file format simply lists values of fields on the nodes of a regular 1D grid, much like the r-grid format used pscf_pc and pscf_pg. Because this program can only use one field file format, the names of commands used by pscf_1d to read and write field files do not contain suffixes that specify a file format.

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