Day 10: Band Structure and DOS Calculation of ZnS¶

The aim of this tutorial is to work through bandstructure and density of states calculations using CASTEP and to exercise the postprocessing and plotting tools. The test system is hexagonal Zinc Sulphide in the Wurtzite structure, and example input files are provided in directory /work4/training/ccp5/abinitio/ZnS/ Make yourself a working directory in your SCARF account and copy the contents of the example directory there. Examine them, and note the .cell block spectral_kpoint_path which generates the list of k-points at which to compute the eigen-energies along a path between the nodes specified. Modify a copy of the SLURM job script you used in the earlier examples, and run your first CASTEP bandstructure calculation. If successful this will generate a file with the extension .bands in addition to the usual .castep output. This will contain the computed eigen-energies at every spectral k-point.

Plotting¶

There is a postprocessing script named dispersion.pl which may either be used on SCARF or copied across to the cloud machine and used there.

#. Usage on SCARF. This assumes that you have set up a working X windows connection to SCARF to display the graphics. There are two supported graphical back-end display programes, either gnuplot or xmgrace. (To access xmgrace on scarf, you need to issue the command module load xmgrace). The command dispersion.pl -gp ZnS-spectral-lda.bands or dispersion.pl -xg ZnS-spectral-lda.bands will produce and display a plot. (Omitting the -xg or -gp plotting arguments will output the raw data as a table to be copyed and plotted by any other program you choose.) Adding the argument --symmetry hexagonal will determine and plot the conventional letter labels for the nodes in the path.

1. Usage on the cloud machine. Copy the dispersion.pl script from /work4/training/ccp5/abinitio/scripts/ and set the executable bit on your copy using chmod +x, and basically follow the instructions as for SCARF.

Effect of XC_Functional¶

Now investigate the effect of changing the XC functional in the calculation. Initially, stick to the pure semi-local XC functionals such as BLYP, PBE, PBEsol, WC which will run quickly.

Calculate the DOS¶

See if you can work out how to change your calculation to compute the DOS instead of the bandstructure. (castep.mpi --help search spectral will give you some suggestions). There is a DOS plotting script partner named dos.pl which will aid with the plotting.

Hybrid functionals¶

Try extending your exploration of the XC functional dependence to one or two of the hybrid functionals especially HSE06 or sX-LDA. These runs will take much longer, so you may want to schedule for an overnight run for analysis tomorrow morning.