Provided by: c2x_2.40+ds-1_amd64 
NAME
c2x - converts various crystal formats including density grid data
SYNOPSIS
c2x [-OPTIONS] [--FORMAT] [--OPERATION] infile [outfile]
DESCRIPTION
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 input and output files from Abinit,
Quantum Espresso and VASP, with some support for Siesta too. 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).
It may have been compiled to give access to symmetry functions from spglib too.
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, ending in '.xsf' is assumed to be in xsf format, and ending in '.xv' or 'XV' is
assumed to be in Siesta's XV format. Input files ending CHG, CHGCAR, POSCAR, CONTCAR,
LOCPOT or WAVECAR are assumed to be in VASP 5.x format. Input files ending in DEN, POT or
WFK are assumed to be in Abinit 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.
OPTIONS
-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 -3.
-A accumulate (sum) bands requested by -b= or -B=.
-b[=range]
include specified bands as psi (real).
-B[=range]
include specified bands as densities (psi*conjg(psi)).
-c include charge density (units electrons per cubic Angstrom).
-C find "compact" (near-cubic) set of cell vectors.
-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.
-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.
-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.
-Dm=[x,y,z]
as above, but also report post-hoc energy correction for a molecule in a cubic box,
or for a molecule in a tetragonal box if dipole moment is parallel to c.
-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.
-e=tol set symmetry tolerance to given number of Angstroms
-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 -.
--formats
list supported formats
--frame=N
extract single frame from series of time steps. Frames are numbered from zero, and
negative numbers represent offsets from the end of the sequence, so --frame=-1 will
extract the final frame. -H shift atoms by half a grid cell. For use with xplor
data format, see below.
-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.
-I[=range]
report whether bands have inversion, and parity under inversion. If combined with
-b or -B, the last range given is used.
-k[=range]
include given kpoints for bands (default range is 1).
-l if k-points are to be included in a .cell file, explicitly list them rather than
using the MP generation parameters.
-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!
-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.
-m[=a,b,c]
assume input is molecule, not crystal. Try to avoid outputing a cell, shift atoms
by fractional co-ordinates given.
-n discard symmetry information, and, if output is XSF, discard forces. Give twice to
discard k-points too.
-N normalise by reducing fractional coords to 0<=x<1. In conjunction with -m, do
output a cell.
-O print band occupancies and evalues to stderr.
-P find primitive cell with own internal algorithm, not spglib.
-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.
-P=p1:rl:nn
output data with cylindrical averaging. p1 is the centre of the cylinder, rl
(literal "r", followed by a length, suffixed by "B" if Bohr) is the radius, and nn
the number of points. The axis of the cylinder must be the c axis, and alpha and
beta must be 90 degrees. Data are averaged over c and theta.
-q calculate post hoc energy correction for charged isolated system. Implies -c.
-q[abc]
calculate post hoc energy correction for charged 2D system. The axis given (a, b or
c) is the aperiodic one. Implies -c.
-Q sort the atoms on output in descending atomic order
-Q2 sort the atoms on output in ascending atomic order
-R don't attempt to rescale densities, but output them raw. Charge density becomes
electrons per unit cell if reading from Castep, for instance. Also do not attempt
to adjust radius to maintain bond length on nanotube creation.
-R=x rescale grid data by factor x, not whatever factor (if any) would normally be used.
If the factor is suffixed by an "x", do include c2x's usual conversion factor too.
-s include spin density.
-S[=range]
include specified spins or spinors for bands (default range is -, and the spins are
numbered 0 and 1).
-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.
-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.
-u use atomic units (Bohrs) when writing .cell files and 1D data. Scale densities from
A^-3 to Bohr^-3 when writing .cube files.
-U scale densities from Bohr^-3 to A^-3 when reading .cube files.
-v be verbose. Far too much output can be generated if specified more than twice.
--version
print version information. If preceeded by -v, also print internal conversion
factors.
-w weight bands by occupancies, or sqrt(occ) if not calculating density.
-w=k weight bands by k-point weight, but not occupancy.
-W weight bands by occupancies and k-point weight, or sqrt thereof if not calculating
density.
-x=(x1,x2,x3)(y1,y2,y3)(z1,z2,z3)
expand unit cell to new cell specified in terms of the old cell axes.
-x=ixjxk
expand cell with a trivial tiling.
-X=(x1,x2,x3)(y1,y2,y3)(z1,z2,z3)
expand unit cell to new cell specified in absolute co-ordinates.
-X[abc]=x
change given axis/axes to new length by inserting / removing vacuum around the
origin. Removing non-existent vacuum will produce nonsense. Length may be suffixed
with B (for Bohr) or nm.
-y=i,j[:x]
make nanotube. The input cell must have c perpendicular to the ab plane, and c as
the nonperiodic direction of the sheet to be rolled. The circumference is then
defined by the vector i*a+j*b. The vector along the tube's length found
automatically, and the size of the cell perpendicular to the tube's length is given
by the optional parameter x, which may be suffixed with B (for Bohr) or nm.
-z=p1 print to stdout data at given point, and set output type to null. For specification
of p1, see -P= option.
-Z=p1 ditto, but assume that data represents an electron density in A^-3, and also output
Perdew Zunger 81 XC energy.
-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.
COMBINING OPERATIONS
The following options expect multiple input files to be given, and perform the specified
operation.
--add Add datasets element-wise.
--diff Subtract datasets element-wise.
--mask Multiply datasets element-wise. Although it is assumed that one dataset will be a
mask of ones and zeros, it need not be so.
--merge
Merge datasets. The expected use is merging an atoms-only format with a density-
only format to create an output containing both atoms and density.
--mult Alternative for --mask.
--sub Alternative for --diff.
--sum Alternative for --add.
When merging, if files contain conflicting data, the one on the right usually has
precidence.
When performing operations on grids, the grids must be the same size. The use of -i may
assist. In all cases, the cells must be the same.
FORMATS
The following output formats are recognised.
--abinit
Abinit .in file. The output is insufficient to be a valid input file to Abinit, but
can easily be made so.
--bands
CASTEP .bands file, no sorting of bands.
--bxsf XCrysDen / FermiSurfer file for plotting Fermi surfaces. A symmetry-reduced kpoint
set will be expanded.
--ccp4 CCP4 density map format. Note no atomic positions can be recorded in this format,
and c2x will always produce a right-hand set of axes unless the input is a lhs and
the option -L is given.
--cell CASTEP .cell, cartesian cell, fractional co-ordinates.
--cell_abc
CASTEP .cell, abc cell, fractional co-ordinates.
--cell_abs
CASTEP .cell, cartesian cell, absolute co-ordinates.
--cell_abc_abs
CASTEP .cell, abc cell, absolute co-ordinates.
--chgcar
VASP 5.x chgcar output.
--cif a very basic and rigid format which may be compatible with some CIF-reading
software.
--cml Chemical Markup Language.
--cube Gaussian cube. Atoms and at most one data set.
--dx Data Explorer. Data set only.
--denfmt
CASTEP formatted density
--fdf Siesta. If a density has been read, a corresponding .RHO file will be written.
--gcoeff
An ASCII wavefunction coefficient representation
--gcoeff_sorted
The same, sorted by |g|
--gnu Gnuplot command file for 1D data.
--null Null output. Throw away all output, but still write some useful information the
input to stderr.
--one Onetep .dat, very similar to .cell. Also one_abc, one_abs, and one_abc_abs.
--pdb PDB
--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.
--py a python dictionary, compatible with the Atoms data structure from ASE.
--pya a python ASE Atoms data structure.
--qe Quantum Espresso. Non colinear spins not supported.
--qef Ditto, atoms in fractional co-ordinates.
--shelx
a subset of the SHELX97 format.
--vasp VASP 5.x output (poscar or chg).
--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 -Hc when creating the pdb file.
--xsf XCrysDen format. Default. The only format in which multiple data sets are
supported.
--xv Siesta's .XV format (positions only, velocities written as zero). Will also write a
.RHO file if grid data have been read.
--xyz XYZ format. Atoms only, no unit cell.
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.
OPERATION
If c2x has been compiled with spglib, the following spglib operations are available.
--int call spg_get_dataset() and report international symbol
--list call spg_get_dataset() and list symmetry ops
--point
call spg_get_dataset() followed by spg_get_pointgroup()
--primitive
call spg_find_primitive(), equivalent to spg_standardize_cell(to_primitive=1,
no_idealize=0). This may rotate the cell to a standardised orientation.
--primitive_nr
call spg_standardize_cell(to_primitive=1, no_idealize=1), so primitive no rotation
--refine
call spg_refine_cell()
--schoen
call spg_get_schoenflies()
--snap call spg_standardize_cell() then expand back to a snapped version of the original
cell
--snap_tr
ditto, but include any translation introduced by spglib
--standardise
call spg_standardize_cell(no_idealize=1)
--std_ideal
call spg_standardize_cell(no_idealize=0)
--symmetry
call spg_get_dataset() and keep symmetry ops
NOTES
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.
When reading a .geom file and writing a format containing a single frame, the last frame
is written.
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 a on the cartesian 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 and cif file formats. 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 and c are exchanged, but the flag -3 will cause
a and b to be exchanged instead.
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.
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.
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.
Densities by default are in Angstroms**-3, and psis in Angstroms**-1.5, save that .RHO
files are written in Bohr**-3 as expected.
EXAMPLES
To extract the charge density in xsf format
c2x -c input.check output.xsf
To extract the first four bands as psi at the second k-point in xsf format
c2x -b=1-4 -k=2 input.check output.xsf
To convert a check file to a pdb file
c2x --pdb input.check output.pdb
To convert a cell to something containing two repeat units in the a and b directions, and
one in the c direction
c2x --cell -x='(2,0,0)(0,2,0)(0,0,1)' in.cell out.cell
or, from c2x version 2.30,
c2x --cell -x=2x2x1 in.cell out.cell
Assuming the above cell was a 3.5A cube, the same in absolute co-ordinates
c2x --cell -X='(7,0,0)(0,7,0)(0,0,3.5)' in.cell out.cell
To change a cell containing one layer of bulk in the c direction to one containing four
layers, and sufficient vacuum to make a total length of 30A
c2x --cell -x=1x1x4 -Xc=30 in.cell out.cell
VIEWERS
The following viewers have been used during the development of c2x: Avogadro, FermiSurfer,
gabedit, Jmol, pymol, VESTA, VMD and XCrysDen.
BUGS
None known.
Please report others to MJR.
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 225 pages 174-179 (2018). http://dx.doi.org/10.1016/j.cpc.2017.12.008
Details of spglib can be found at https://atztogo.github.io/spglib/
SEE ALSO
babel(1)
https://www.c2x.org.uk/
c2x(1)