C2x: A tool for visualisation and input preparation for Castep and other electronic structure codes

Abstract

The c2x code fills two distinct roles. Its first role is in acting as a converter between the binary format .check files from the widely-used Castep[1] electronic structure code and various visualisation programs. Its second role is to manipulate and analyse the input and output files from a variety of electronic structure codes, including Castep, Onetep and Vasp, as well as the widelyused 'Gaussian cube' file format. Analysis includes symmetry analysis, and manipulation arbitrary cell transformations. It continues to be under development, with growing functionality, and is written in a form which would make it easy to extend it to working directly with files from other electronic structure codes.Data which c2x is capable of extracting from Castep's binary checkpoint files include charge densities, spin densities, wavefunctions, relaxed atomic positions, forces, the Fermi level, the total energy, and symmetry operations. It can recreate .cell input files from checkpoint files. Volumetric data can be output in formats usable by many common visualisation programs, and c2x will itself calculate integrals, expand data into supercells, and interpolate data via combinations of Fourier and trilinear interpolation. It can extract data along arbitrary lines (such as lines between atoms) as 1D output.C2x is able to convert between several common formats for describing molecules and crystals, including the .cell format of Castep. It can construct supercells, reduce cells to their primitive form, and add specified k-point meshes. It uses the spglib library[2] to report symmetry information, which it can add to .cell files.C2x is a command-line utility, so is readily included in scripts. It is available under the GPL and can be obtained from http://www.c2x.org.uk. It is believed to be the only open-source code which can read Castep's .check files, so it will have utility in other projects.

Optical absorption driven by dynamical symmetry breaking in indium oxide

“…Electronic and optical properties of In2O3 at the BZ center. Band energies are measured with respect to the valence band maximum, and we report the band degeneracies, parities (determined using c2x [53]), and the optical matrix elements |McvΓ| 2 = | ψcΓ|ê • p|ψvΓ | 2 between the CBM at 3.032 eV and a number of valence band states. Results are shown at the static lattice level, and for thermal line distortions [54] corresponding to 0 K (zero-point motion) and 300 K. For bands that are degenerate at the static lattice level, we consider the average over the optical matrix elements at 0 K and 300 K.…”

Electronic properties of the Sn1−xPbxO alloy and band alignment of the SnO/PbO system: a DFT study

“…We have performed DFT calculations in order to obtain the work function. For this scope, a SnO 2 × 2 × 6 supercell with a total of 96 atoms and a vacuum of 25 Å was used for the calculations and the average electrostatic potential along the z axis (001 direction) was calculated with the help of the c2x tool 37 . The work function, W , was then calculated as where V vac is the vacuum potential and E F the Fermi energy for the SnO and PbO structures.…”

“…For this scope, a SnO 2 × 2 × 6 supercell with a total of 96 atoms and a vacuum of 25 Å was used for the calculations and the average electrostatic potential along the z axis (001 direction) was calculated with the help of the c2x tool 37 10 . The work function of PbO has been measured between 4.8 and 5.5 eV, depending on growth conditions 38 .…”

Vapor–liquid–solid growth and properties of one dimensional PbO and PbO/SnO2 nanowires

“…46 For the calculation of the work function, we have performed DOS calculations using supercells of 8 layers (8 Â 1 Â 1) and a vacuum of B20 Å. The electrostatic potential was calculated using the c2x tool 47 and the vacuum energy level was extracted. Then, the work function was calculated as: W = V vac À E Fermi .…”