Parameter File - pscf_1d (Prev) Field Files (Next)

The pscf_pc and pscf_pg programs for periodic systems use nearly identical parameter file formats, and so are discussed together here. The description given here only discusses parameter file elements that are relevant to SCFT calculations. A complete description of the parameter file format for either of these programs, including optional elements that not relevant to SCFT, is given here.

Example

The example show below is a typical parameter file for using either pscf_pc or pscf_pg to perform a single SCFT calculation for a 3D structure of a diblock copolymer melt using a known space group.

System{
  polymerModel thread
  Mixture{
    nMonomer  2
    monomers[
              1.0
              1.0
    ]
    nPolymer  1
    Polymer{
      type    linear
      nBlock  2
      blocks[
              0  0.15
              1  0.85
      ]
      phi     1.0
    }
    ds   0.01
  }
  Interaction{
    chi(
          1   0   25.0
    )
  }
  Domain{
    mesh             32  32  32
    lattice          cubic
    groupName        I_m_-3_m
  }
  Iterator{
    epsilon      1e-10
    isFlexible   1
  }
}

This parameter file is designed to initialize a single SCFT calculation for a BCC phase of a single-component diblock copolymer melt, using a flexible unit cell. The Domain block of this file contains an optional groupName parameter that gives the identifier for the space group of a BCC phase. A parameter file for SCFT calculation of a mixture could contain more than one "Polymer" blocks and/or one or more "Solvent" blocks. A parameter file that is used to initialize a SCFT parameter sweep would also contain an additional "Sweep" block.

File format

The elements of a parameter file used by pscf_pc or pscf_pg to perform a SCFT or an SCFT parameter sweep are shown in skeleton from below:

System{
  polymerModel*  string  ("thread" or "bead", "thread" by default)
  Mixture{ ...  }
  Interaction{ ...  }
  Domain{ ...  }
  Environment#*{ ...  }
  Iterator#*{ ... }
  Sweep#*{ ... }
}

The above skeleton only includes blocks that are relevant to SCFT calculations. It does not include an optional "Simulation" block that is only used for a PS-FTS calculation. A complete description of all allowed elements of the main System block is given here.

Parameter file formats of the Mixture and Interaction blocks are the same (or nearly so) for all PSCF programs, and have been discussed previously. The other elements of this file format are discussed below:

PolymerModel parameter

The optional polymerModel is a string parameter with allowed values of "thread" and "bead". These values specify global use of either the continuous thread ("thread") or discrete bead ("bead") model, respectively
The polymerModel parameter is the first entry in the System block for a pscf_pc or pscf_pg parameter file, which must appear before the Mixture block. If the polymerModel parameter is omitted, the thread model is used by default.

This parameter may not be used in the parameter file for pscf_1d because this program only allows use of the thread model.

Domain block

The Domain block contains information required to describe the unit cell of a periodic structure, the regular mesh that is used to discretize fields within each unit cell, and (optionally) an identifier for the space group of an SCFT solution. The format of this block has been discussed in detail on a previous page.

Environment

The Environment block is an optional selectable block that can be used to define a mask and/or external potential fields in order to define an inhomogeneous externally imposed environment, as discussed in detail here. An environment can be used to describe a confined environment such as that experienced by a thin film.

An Environment block is not needed for standard SCFT calculations involving bulk periodic phases, and so does not appear in the above example.

Iterator

The pscf_pc and pscf_pg programs each provide two SCFT iterator algorithms named AmIteratorBasis and AmIteratorGrid, as discussed on a previous page.

AmIteratorBasis is the default iterator algorithm for both pscf_pc and pscf_pg. The above example uses the generic "Iterator" block label to invoke this algorithm, which is an Anderson mixing algorithm that preserves the space-group symmetry specified in the Domain block.

The Iterator block of the parameter file is formally optional in the parameter file format for pscf_pc and pscf_pg. Either program can thus successfully finish reading the parameter file if this block is absent. A valid Iterator block must be present, however, to actually perform a SCFT calculation. The Iterator block is treated as optional element of pscf_pc and pscf_pg parameter files because both of these programs can also perform PS-FTS calculations, as well as SCFT, and an Iterator is not needed for such simulations.

Sweep

The Sweep block is optional block that is used to program a SCFT parameter sweep. It has been programmed as a selectable block, but there is currently only one available sweep algorithm for either pscf_pc or pscf_pg, which is a general linear sweep algorithm that is implemented by a class named LinearSweep. Because this is also the default sweep algorithm, it may be enabled by including a Sweep block that starts with either with the generic label "Sweep" or the specific label "LinearSweep". The format of the required parameter file block has been described on a previous page. A Sweep block is allowed only if an Iterator block is present.

The above example does not contains a Sweep block.