.TH c2x 1
.SH NAME
c2x - converts various crystal formats including density grid data
.SH SYNOPSIS
.B c2x
[-OPTIONS] [--FORMAT] [--OPERATION] infile [outfile]
.SH DESCRIPTION
.B c2x
converts primarily a CASTEP .check file to various output formats,
additionally extracting densities (charge, spin, band or psi) and forces. It
can also read CASTEP .cell files and PDB files, Onetep .dat files,
and several VASP input and output files. It is a sort of Babel with
support for gridded data and .check files, and the ability to transform
cells and perform simple analysis (integration, interpolation, dipole
moment calculation, band parity identification).
.LP
It may have been compiled to give access to symmetry functions from spglib
too.
.LP
An input file whose name ends '.pdb' is assumed to be in pdb format,
ending in '.cif' is assumed to be in cif format, ending in '.res' is
assumed to be in shelx97, ending '.cub' or '.cube' is assumed to be in
cube format, ending '.in' is assumed to be an Abinit or Quantum Espresso
input file, ending '.xml' is assumed to be a Quantum Espresso output
file, and ending in '.xsf' is assumed to be in xsf format. Input
files ending CHG, CHGCAR, POSCAR or CONTCAR are assumed to be in VASP
5.x format. Otherwise, if the first byte is either zero, 10 or 30 it is
assumed to be a .check file, else it is assumed to be a .cell file. It
can also read .orbitals files (which are identical to .check files in
format), and .castep_bin files (which lack wavefunctions). Furthermore,
it can read .chdiff files and .cst_esp files. In these cases it needs
a .cell or a .check file as well in order to obtain unit cell information.
.SH OPTIONS
.LP
.TP
.B \-a
rotate as though outputing in abc format, i.e. place a along x axis, b
in xy plane, and abc form a right hand set. Useful if one wants a dx file
consistent with a pdb file. See also
.BR \-3 .
.TP
.B \-A
accumulate (sum) bands requested by
.B \-b=
or
.BR \-B= .
.TP
.B \-b[=range]
include specified bands as psi (real).
.TP
.B \-B[=range]
include specified bands as densities (psi*conjg(psi)).
.TP
.B \-c
include charge density (units electrons per cubic Angstrom).
.TP
.B \-C
find "compact" (near-cubic) set of cell vectors.
.TP
.B \-d
read also a corresponding .chdiff file, and output its contents. The filename
given must still be that of a .cell or .check file, as a .chdiff file
contains no axes.
.TP
.B \-D=[x,y,z]
if charge density read (-c), calculate dipole moment about fractional
co-ordinates x,y,z, or 0.5,0.5,0.5 if co-ordinates not given. Assumes
density has been read as eA^-3.
.TP
.B \-Da=[x,y,z]
as above, but also report post-hoc energy correction for slab geometry for
the a axis being the non-periodic axis. Valid values of a: a, b and c.
.TP
.B \-Dm=[x,y,z]
as above, but also report post-hoc energy correction for a molecule in
a cubic box.
.TP
.B \-e
read also a corresponding .cst_esp file, and output its contents. The filename
given must still be that of a .cell or .check file, as a .cst_esp file
contains no axes.
.TP
.B \-e=tol
set symmetry tolerance to given number of Angstroms
.TP
.B \-E[=[-][mu]]
calculate electrostatic potential, assuming that an electron density has been
read (implies -c). Ions are treated as Gaussian blobs of charge of
extent exp(-mu^2r^2). If the ionic charge differs from the atomic number,
a further localised smoothing of the atomic potential occurs, unless the first
character after the = is -.
.TP
.B \-H
shift atoms by half a grid cell. For use with xplor data format, see below.
.TP
.B \-i=nx,ny,nz
Fourier interpolate onto specified grid size. New grid may be coarser or finer
than original. Any dimension given as zero is replaced by old grid size. If
reading wavefunction, any grid truncation is done after transforming back to
real space and converting to density etc.
.TP
.B \-I[=range]
report whether bands have inversion, and parity under inversion. If combined
with -b or -B, the last range given is used.
.TP
.B \-k[=range]
include given kpoints for bands (default range is 1).
.TP
.B \-l
if k-points are to be included in a .cell file, explicitly list them rather
than using the MP generation parameters.
.TP
.B \-L
output in abc format assuming that abc describes a left-handed set of axes.
Do not use this unless you understand why you should not!
.TP
.B \-m[=a,b,c]
assume input is molecule, not crystal. Try to avoid outputing a cell,
shift if some co-ordinates are negative, or if a,b,c given shift by
those numbers of FFT grid cells.
.TP
.B \-O
print band occupancies and evalues to stderr.
.TP
.B \-P
find primitive cell.
.TP
.B \-P=p1:p2:nn
output data as line of nn points from p1 to p2. Express p's as either
fractional co-ordinates in the form (x,y,z), or an atom position as, e.g.,
Si3 for silicon atom number 3, or simply Si for the first Si atom. Using
a 0 (zero) for a p is equivalent to (0,0,0), and the three cell axes
"(0,0,0):(1,0,0):ngx+1" (etc.) can be specified as a, b and c.
.TP
.B \-R
don't attempt to rescale densities, but output them raw. Charge density
becomes electrons per unit cell.
.TP
.B \-s
include spin density.
.TP
.B \-S[=range]
include specified spins or spinors for bands (default range is -, and
the spins are numbered 0 and 1).
.TP
.B \-t=(x1,y1,z1)(x2,y2,z2)[(x3,y3,z3)]
rotate co-ordinate system so that the first vector becomes the second. First
vector given in relative co-ordinates. If third axis given, it is used as
the rotation axis. Else the rotation axis will be perpendicular to the
two axes given.
.TP
.B \-T=(x1,y1,z1)(x2,y2,z2)[(x3,y3,z3)]
rotate co-ordinate system so that the first vector becomes the second. All
vectors given in absolute co-ordinates. If third axis given, it is used as
the rotation axis. Else the rotation axis will be perpendicular to the
two axes given.
.TP
.B \-u
use atomic units (Bohrs) when writing .cell files and 1D data. Scale
densities from A^-3 to Bohr^-3 when writing .cube files.
.TP
.B \-U
scale densities from Bohr^-3 to A^-3 when reading .cube files.
.TP
.B \-v
be verbose. Far too much output can be generated if specified more than twice.
.TP
.B \-\-version
print version information. If preceeded by -v, also print internal conversion
factors.
.TP
.B \-w
weight bands by occupancies, or sqrt(occ) if not calculating density.
.B \-W
weight bands by occupancies and k-point weight, or sqrt thereof if not
calculating density.
.TP
.B \-x=(x1,x2,x3)(y1,y2,y3)(z1,z2,z3)
expand unit cell to new cell specified in terms of the old cell axes.
.TP
.B \-X=(x1,x2,x3)(y1,y2,y3)(z1,z2,z3)
expand unit cell to new cell specified in absolute co-ordinates.
.TP
.B \-z=p1
print to stdout data at given point, and set output type to null. For
specification of p1, see -P= option.
.TP
.B \-1
assume input .cell file follows Onetep conventions (such as default units
being Bohr).
.TP
.B \-3
when moving from a left hand set of axes to a right hand set, rather than
exchanging the 2nd and 3rd axes, preserve the 3rd and exchange the 1st
and 2nd. This transformation is required if the input is cartesian and
left handed, and an abc output is requested. Specifying this flag twice
will cause the 1st and 3rd axes to be exchanged.
.SH FORMATS
.LP
The following output formats are recognised.
.TP
.B \-\-abinit
Abinit .in file. The output is insufficient to be a valid input file to
Abinit, but can easily be made so.
.TP
.B \-\-cell
CASTEP .cell, cartesian cell, fractional co-ordinates. The output contains
just the lattice and positions blocks, so is not a valid input to CASTEP, but
can easily be made so.
.TP
.B \-\-cell_abc
CASTEP .cell, abc cell, fractional co-ordinates.
.TP
.B \-\-cell_abs
CASTEP .cell, cartesian cell, absolute co-ordinates.
.TP
.B \-\-cell_abc_abs
CASTEP .cell, abc cell, absolute co-ordinates.
.TP
.B \-\-chgcar
VASP 5.x chgcar output.
.TP
.B \-\-cif
a very basic and rigid format which may be compatible with some CIF-reading
software.
.TP
.B \-\-cml
Chemical Markup Language.
.TP
.B \-\-cube
Gaussian cube. Atoms and at most one data set.
.TP
.B \-\-dx
Data Explorer. Data set only.
.TP
.B \-\-denfmt
CASTEP formatted density
.TP
.B \-\-fdf
Siesta. Current support is very partial. If you want a density, you must
name the output file on the command line, the filename must end ".fdf",
and the density will appear in a corresponding ".RHO" file.
.TP
.B \-\-gnu
Gnuplot command file for 1D data.
.TP
.B \-\-null
Null output. Throw away all output, but still write some useful information
the input to stderr.
.TP
.B \-\-one
Onetep .dat, very similar to .cell. Also one_abc, one_abs, and one_abc_abs.
.TP
.B \-\-pdb
PDB
.TP
.B \-\-pdbn
PDB, but label the atoms with element symbol and number within that species,
e.g. C8, H24, Ca2, rather than just with element symbol. The whole string
can contain no more than four characters, so * is used for the numeric part
if it would not otherwise fit.
.TP
.B \-\-py
a python dictionary, compatible with the Atoms data structure from ASE.
.TP
.B \-\-pya
a python ASE Atoms data structure.
.TP
.B \-\-qe
Quantum Espresso. Non colinear spins not supported.
.TP
.B \-\-qef
Ditto, atoms in fractional co-ordinates.
.TP
.B \-\-shelx
a subset of the SHELX97 format.
.TP
.B \-\-vasp
VASP 5.x output (poscar or chg).
.TP
.B \-\-xplor
Xplor format. Data set only. The grid used in this format is offset by half
a grid cell compared to Castep, and as interpolating is inexact, this program
does not in this case. Also the grid axes are described in terms of a, b, c,
alpha, beta, gamma, so information about orientation in space is lost. To
produce a compatible pdb file of atomic co-ordinates, specify
.I \-Hc
when creating the pdb file.
.TP
.B \-\-xsf
XCrysDen format. Default. The only format in which multiple data sets are
supported.
.TP
.B \-\-xyz
XYZ format. Atoms only, no unit cell.
.LP
Where a range is required, it can be specified as a single integer, two
integers separated by a hyphen (all integers in the given range), or a
comma-separated list of any of these elements. Only for the xsf output format
is a range including more than a single integer meaningful.
.SH OPERATION
.LP
If c2x has been compiled with spglib, the following spglib
operations are available.
.TP
.B \-\-int
call spg_get_dataset() and report international symbol
.TP
.B \-\-list
call spg_get_dataset() and list symmetry ops
.TP
.B \-\-point
call spg_get_dataset() followed by spg_get_pointgroup()
.TP
.B \-\-primitive
call spg_find_primitive()
.TP
.B \-\-refine
call spg_refine_cell()
.TP
.B \-\-schoen
call spg_get_schoenflies()
.TP
.B \-\-snap
call spg_standardize_cell() then expand back to a snapped version of the
original cell
.TP
.B \-\-standardise
call spg_standardize_cell(no_idealize=1)
.TP
.B \-\-symmetry
call spg_get_dataset() and keep symmetry ops
.SH NOTES
.LP
For the pdb formats, just the unit cell and atomic positions are read or
written. For the dx and xplor formats, just a single data set is written.
For the Gaussian cube format atomic positions and at most one data set
are recorded, and for the XCrysDen format the unit cell, atomic positions,
forces, and any number of data sets are recorded.
.LP
Note that the pdb format offers a very low precision for storing co-ordinates,
and, because it stores the unit cell in abc format, and the atoms in absolute
coordinates, a rotation is likely to be required to place
.B a
on the cartesian
.B x
axis, etc. If so, it will be done automatically. The same is true for the abc
varients of the cell format and for the Xplor file format. This rotation can be
specified explicitly for other formats. Additionally the axes must form
a right-handed set. If this is not the case, two axes will be interchanged.
By default,
.B b
and
.B c
are exchanged, but the flag
.B \-3
will cause
.B a
and
.B b
to be exchanged instead.
.LP
The cif reader reads little more than c2x's cif output. It is very
basic, and will fail to read correctly a large number of valid cif files.
There is currently no intention to produce a proper cif reader.
.LP
When outputting psi it is assumed that it is possible to make psi real
by unwinding any phase produced by the k-point, and then multiplying
all points by the same arbitrary complex constant. If this is not so,
the band was probably nonsense anyway. The final choice of a factor of
-1 is arbitrary. This scheme produces nonsense if one attempts to
plot a degenerate band.
.LP
When doing the conversions resulting from -x, a new grid will be
chosen of similar density to the old, and the data interpolated onto
the new using trilinear interpolation. Extrapolating psis (rather than
densities) is meaningless except at gamma, for the phase due to the k
point is not considered.
.LP
Densities by default are in Angstroms**-3, and psis in Angstroms**-1.5.
.SH EXAMPLES
.LP
To extract the charge density in xsf format
.IP
c2x -c input.check output.xsf
.LP
To extract the first four bands as psi at the second k-point in xsf format
.IP
c2x -b=1-4 -k=2 input.check output.xsf
.LP
To convert a check file to a pdb file
.IP
c2x --pdb input.check output.pdb
.LP
To convert a cell to something containing two repeat units in the a
and b directions, and one in the c direction
.IP
c2x --cell -x='(2,0,0)(0,2,0)(0,0,1)' in.cell out.cell
.LP
Assuming the above cell was a 3.5A cube, the same in absolute co-ordinates
.IP
c2x --cell -x='(7,0,0)(0,7,0)(0,0,3.5)' in.cell out.cell
.SH VIEWERS
This code was written with the following viewers in mind. For densities,
xcrysden, VESTA and jmol, for structures gdis.
.SH BUGS
None known.
Please report others to MJR.
.SH ACKNOWLEGEMENTS
If you wish to cite, please do so as "C2x: a tool for visualisation
and input preparation for Castep and other electronic structure
codes", MJ Rutter, Computer Physics Communications, vol 225C pages
152-157 (2018).
Details of spglib can be found at https://atztogo.github.io/spglib/
.SH SEE ALSO
babel(1).