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PSCF v1.1
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Field File - 1D Fields (pscf_fd) (Prev) Command Files (Next)
The pscf_pcN and pscf_pgN programs are both designed to treat periodic structures, and use the same set of several field file formats.
The pscf_pc and pscf_pg programs can all read and write fields using following three field file formats:
Each of these file formats for periodic structures contains a header section that includes a specification of the crystal system and unit and unit cell parameters for the crystallographic unit cell. The header for the r-grid and k-grid format also contains a list of the mesh dimensions, i.e., the number of grid points in each direction of the mesh that was used by the program that wrote the file.
The dimensions of the mesh used by the program that reads a file in r-grid or k-grid format (as given in the parameter file) must match the dimensions of the mesh used by the program that wrote the file (as declared in the field file header for these formats).
The basis format is instead designed to allow users to change mesh dimensions: A instance of a program for which a particular list of mesh dimensions is declared in the parameter file can usually read and correctly intepret a field file that was created using a basis designed for a different mesh. (There are still occasional situations in which this translation fails, which we in the process of fixing). The basis format can thus usually be used to change resolution by, for example, using a converged solution obtained with a coarse mesh as an initial guess for the solution on a refined mesh.
The current C++ version of PSCF can also read the basis and r-grid file formats used by the older Fortran PSCF program. The k-grid format used by the current version is not backwards compatible with the analogous k-grid format used by the Fortran program.
The names of some command-file commands that instruct pscf_pc and pscf_pg programs to read or write field files contain the strings "BASIS", "RGRID", or "KGRID" to indicate the use of a particular field file format.
Each of the three field file formats described above contains a header section followed by a data section. The header section has an almost identical form in all three file formats, and contains information about the dimensionality of space, the crystallographic unit cell, the space group, and the mesh or basis used to represent the fields.
As an example, here is header section of a r-grid field file for a double gyroid phase (space group \( Ia \overline{3}d \) that was computed using a mesh with 32 grid points along each of three orthogonal directions:
The first line of the header specifies a file format version number (file format v1.0).
The rest of the header contains parameter values, each of which is given as a parameter label on one line followed by a value on the next line. The header of a field file may contain values for the following parameters, in the following order:
dim : The value of the parameter dim is number of dimension in which each field is periodic. For example, dim=1 for a lamellar phase, dim=2 for a hexagonal phase, and dim=3 for a 3D cubic or orthorhombic crystal. This quantity is also referred to by the symbol D throughout the source code and in some other parts of the web documentation.
crystal_system : The parameter crystal_system is a string identifer for the crystal system, i.e., the type of Bravais lattice. Allowed values of this string for each value of dim are listed here.
N_cell_param : The parameter N_cell_param is a positive integer that gives the number of real parameters that are required to describe the unit cell for the specified crystal_system. This number can range from 1 for 1D lamellar, 2D square or hexagonal or 3D cubic crystals, 3 from for a 3D orthorhombic crystal, up to 6 for a 3D triclinic lattice.
cell_param : The value of cell_param is a list of N_cell_param real numbers required to describe the unit cell, separated by spaces. These parameters generally specify lengths of Bravais basis vectors or unit cell edges and (when required) angles between those vectors. The number, order, and the meaning of those parameters depends upon the value of the crystal_system identifier, as discussed here.
group_name : The parameter group_name is a string identifier for a crystallographic space group. Allowed values of this identifier string for each combination of values for dim and crystal_system are listed here.
N_monomer : The parameter N_monomer is a positive integers that gives the number of distinct monomer types for which fields are reported.
N_basis : The parameter N_basis is a positive integer that gives the number of basis functions used in a Fourier-adapted Fourier series representation of the fields. A label "N_star" will also be accepted as a synonym for "N_basis", to preserve backwards compatability with the label used by the older PSCF fortran program. This parameter only appears in the basis file format.
mesh : The mesh parameter is a list of dim positive integers that give the mesh dimensions used for numerical calculations, i.e., the number of grid points in each direction in the mesh that covers a single unit cell. A label "ngrid" will also be accepted as a synonym for "mesh", to allow backwards compatibility with the label used by the PSCF Fortran program. This list of values appears as the last parameter of the header for r-grid and k-grid file formats, but does not appear in the basis format.
All of these parameters except mesh and N_basis are required elements of the header in all three file formats.
The three field file formats for periodic fields are described in more detail in the sub-pages linked below:
Field File - 1D Fields (pscf_fd) (Prev) Field Files (Up) Command Files (Next)
1.9.5