# multishifter

casm powered utility to create gamma surfaces, UBER curves, and twisted bilayers along crystal planes.

View the Project on GitHub goirijo/multishifter

# Tutorial I: Slicing a structure

In this tutorial we’ll use multishift slice to create a structure of $$\mathrm{Mg}$$ with ab-vectors in the $$(0,\bar{1},1)$$ plane (pyramidal slip plane).

## Mg primitive cell

Current implementations of multishifter work exclusively with the VASP structure format. Download the primitive cell for $$\mathrm{Mg}$$ here, or create a file called mg.vasp with the following crystallographic data:

multishifter tutorial i
1.00000000
1.59609453       2.76451683       0.00000000
-1.59609453       2.76451683       0.00000000
0.00000000       0.00000000       5.18401957
Mg
2
Direct
0.6666667    0.6666667    0.7500000 Mg
0.3333333    0.3333333    0.2500000 Mg


The figure below on the left shows the primitive unit cell of $$\mathrm{Mg}$$, while the one on the right highlights the prismatic plane. This is the slip plane we’re interested in, and has miller indices $$(0,\bar{1},1)$$.

## Slice the structure

multishift slice --input mg.vasp --millers 0 -1 1 --output mg_pyramidal.vasp


This will read mg.vasp as the starting structure, and slice it allong the specified miller indexes, saving the generated structure to mg_pyramidal.vasp.

## Output

You will now have a file named mg_pyramidal.vasp. The plane defined by the millers argument is spanned by the $$ab$$ vectors of this structure. By default, the slice command also performs a rigid rotation on the final structure, aligning the $$a$$ vector along the $$x$$ direction, and the $$b$$ vector in the $$xy$$ plane. This final rotation can be supressed by using the flag --dont-align. The rotation can also be applied to any structure using multishift align.

## Slicing graphite

In the previous example, the sliced structure was still a primitive cell, albeit with an unconventional definition. If we slice the primitive cell of graphite along the $$(1,1,1)$$ layers, we’ll see this isn’t always the case.

Download the primitive cell for graphite here, or create a file called graphite.vasp with the following cyrstallographic data:

multishifter tutorial i.b
1.0
4.2654600143         0.0000000000         0.0000000000
3.5512614760         2.3627719025         0.0000000000
3.5512614760         1.0734450299         2.1048531614
C
2
Direct
0.166667989         0.166668006         0.166667997
0.833331925         0.833332067         0.833331971


You can repeat the slice command with new parameters now:

multishift slice --input graphite.vasp --millers 1 1 1 --output graphite_sliced.vasp


The resulting structure is a size 3 superstructure of the starting primitive structure, but has $$ab$$ vectors parallel to the individual graphene layers. The figure below contrasts the primitive cell with the sliced structure.