MgO with atomic projections

Note

The files needed for this example are provided in the examples/MgO folder.

Often it is useful to know the various contributions of atoms in the structure to the electronic bands in the band structure, to analyse the chemistry and orbital interactions at play in the system. This can be computed for unfolded bands as well.

For a normal band structure calculation, the contributions can be inferred by colouring the band according to the elemental contributions, which can be done using sumo.

Band structure of MgO with atomic contribution

Similar plots can be generated for unfolded band structures. However, because the unfolded spectral function itself contains both the location of the band and its intensity, adding a third dimension of information (atomic projection) can be tricky to visualise.

In this example, we unfold the bands from a MgO 2x1x2 supercell with a Mg atom displaced to break symmetry. The procedure is essentially the same as described in the Si supercell example.

The only difference here is that we turn on the calculation of orbital projections in VASP with LORBIT = 11 (12, 13 and 14 will also work) in the INCAR file, and then use the plot-projections subcommand when plotting the unfolded band structure:

easyunfold unfold plot-projections --procar MgO_super/PROCAR --atoms="Mg,O" --combined --emin=-6 \
--emax=20 --intensity 6.5

Note that the path of the PROCAR is passed along with the desired atom projections (Mg and O here).

Tip

If the k-points have been split into multiple calculations (e.g. hybrid DFT band structures), the --procar option should be passed multiple times to specify the path to each split PROCAR file (i.e. --procar calc1/PROCAR --procar cal2/PROCAR ...).

Note

The atomic projections are not stored in the easyunfold.json data file, so the PROCAR file(s) should be kept for replotting in the future.

The --combined option creates a combined plot with different colour maps for each atomic grouping. The spectral intensity is used to define the transparency (alpha) allowing the fusion of multiple projections into a single plot.

Unfolded MgO band structure with atomic projections.

The default colour map for atom projections is red, green, blue and purple for the 1st, 2nd, 3rd and 4th atomic species specified. This can be changed with the --colours option, as well as several other plotting/visualisation settings – see the output of easyunfold unfold plot-projections --help for more details. If we wanted to plot the atomic projections with the same colouring scheme as the sumo plot above (i.e. red for Mg and blue for O), we can use:

easyunfold unfold plot-projections --procar MgO_super/PROCAR --atoms="Mg,O" --combined --emin=-6 \
--emax=20 --intensity 6.5 --colours "r,b"

Unfolded MgO band structure with atomic projections; red for Mg and blue for O atoms.

Note

In order to specify the atomic projections with --atoms, the POSCAR or CONTCAR file for the supercell must be present. If this is not the case, or we want to use projections from only specific atom subsets in the supercell, we can alternatively use the --atoms-idx tag. This takes a string of the form a-b|c-d|e-f where a, b, c, d, e and f are integers corresponding to the atom indices in the VASP structure file (i.e. POSCAR/CONTCAR, corresponding to the PROCAR being used to obtain the projections). Different groups are separated by |, and - can be used to define the range for each projected atom type. A comma-separated list can also be used instead of ranges with hyphens. Note that 1-based indexing is used for atoms, matching the convention in VASP, which is then converted to zero-based indexing internally in python. In this example, we could set --atoms-idx="1-4|5-8" to get the same result as --atoms="Mg,O" (but without the figure legend).

In some cases, especially if there are many projection to be plotted at the same time, it can be clearer to create separated plots for each. This is the default behaviour for plot-projections, when --combined is not specified.

easyunfold unfold plot-projections --procar MgO_super/PROCAR --atoms="Mg,O" --emin=-6 \
--emax=20 --intensity 6.5

Unfolded MgO band structure with atomic projections plotted separately.

Tip

There are many customisation options available for the plotting functions in easyunfold. See easyunfold plot -h or easyunfold unfold plot-projections -h for more details!