User Guide

  There are two versions of the application, one for analysing the output from CASTEP, the other for CETEP. Both versions have a number of features in common.

The atom types must be defined in a file called defs.file.This must contain one entry for each atom species with the following format:

Species Symbol
Net ionic charge
Filename of S radial wavefunction (NULL if not present)
Filename of P radial wavefunction (NULL if not present)
Filename of D radial wavefunction (NULL if not present)
Filename of externally generated orbitals (NULL if not present)
Number of orbitals

There must be no blank lines and the atomic species must be in the same order as given in the data files for the CASTEP/CETEP run. If externally generated orbitals are used (see later) the wavefunctions defined in the previous 3 entries will be ignored. All filenames must be a maximum of 30 characters in length. An example file is given in the top directory of the distribution.

The radial wavefunction files give the radial wavefunction in real space on a logarithmic grid. Each line consists of a value for r followed by a value for the wavefunction at that radius separated by a space. The r values should be monotonically increasing. These files are generated by the atom program. Generally, the radial wavefunctions corresponding to the valence shell of the appropriate pseudopotential are used. A library of pseudo-orbitals is provided in the directory Orbitals in the top directory of this distribution. Please see the README file in this directory for information on the source of these orbitals. If you require other pseudo-orbitals, please contact the author.

You may generate your own localised basis set and load the orbitals from a file specified in the 6th entry for the atomic species in defs.file. These must be for a single atom of the appropriate species at the origin of the cell and represented on a reciprocal space grid created with the same unit cell, FFT grid and cut off energy as the calculation to be analysed. The file format is the same as the wavefunctions for the version of CASTEP/CETEP being analysed. If you are not familiar with the wavefunction file formats of CASTEP or CETEP, you are strongly discouraged from using this option.

A file, param.file, defines the parameters for the population analysis. These files differ between the CASTEP and CETEP versions of the application are are described in Subsection 3.1 and 3.2 respectively.

The output wavefunctions and occupancies (if present) must be provided to perform the population analysis. Also, the file defining the positions of the atoms must be present. The filenames for these are version specific and are also described in the appropriate subsections.

The population analysis is a 2-stage operation. First the overlap and density matrixes are generated by running the command:

[cetep_]overlap

This gives a progress report on the standard output including the value of the spilling parameter. If the band-by-band option is enabled (this may be set in param.file) a file called bb.out is created containing the weights of each band in each orbital for each k-point and the spilling parameter of each band for each k-point. A file matrix.out containing the overlap and density matrixes is created which may then be analysed to give the Mulliken populations using the command:

[cetep_]mulliken

The results are printed to the standard output and consist of the net occupancy of each orbital, the overlap population between each pair of atoms and the net charge on each atom.

The population analysis process has been split into two parts because other population analyses can be performed using the overlap and density matrixes, for example those due to Lowdin [7], Roby [8] and Mayer [9,10]. Codes may be written to perform these analyses using the output from the overlap application.