you can read this paper

https://www.persee.fr/doc/bulmi_0180-9210_1986_act_109_1_7921

Hello Eric Welch ,

This can probably be done with Vesta but I imagine this to be a bit tedious. When it comes to creating more complicated surfaces/interfaces I'd recommend you to move to Python and the Pymatgen module. While the learning curve might be more difficult in the beginning it will pay back if you are planning to do similar things in the future.

Good luck!

-Peter

Thank you for the answers!! I will check that paper and look into Pynatgen

At least in principle, this should not be too difficult, since the hexagonal stacking along the c-axis and the fcc stacking along the 111 axis are both close-packed structures, the hexagonal one being an ABABAB... sequence, whereas the fcc one is an ABCABCABC... sequence. (For some relevant illustrations, have a look at https://www.tf.uni-kiel.de/matwis/amat/mw_for_et/kap_3/backbone/r3_2_1.html -- just don't be afraid that this is in German.) Both wurtzite and diamond/zinc-blende just possess an additional atom along the stacking direction, but this doesn't change the general stacking sequence.

In fact, such an interface was already investigated quite some years ago by some former colleagues of mine for the case of silicon carbide: "Heterocrystalline Structures: New Types of Superlattices?" and "Properties of interfaces between cubic and hexagonal polytypes of silicon carbide" (the relevant links are given below). A different group has investigated the heterocrystalline interface in cadmium sulfide (also given below).

Article Heterocrystalline Structures: New Types of Superlattices?

Article Properties of interfaces between cubic and hexagonal polytyp...

Article Revisiting the Zinc-Blende/Wurtzite Heterocrystalline Structure in CdS

Jan-Martin Wagner thank you so much for the comment and articles!! I will have a look at them

I give you a not so-short circumventing way. You can assume the transition to be coherent, so it may be unable to catch elastic strain on interface and variation of this stress field normal to transition interface.

• Start with a standard cubic zinc blende structure in VESTA
• Go to edit>edit data> unit cell> transform
• Change the basis vectors such that one of the vectors point to direction (say, the new z), other to any suitable direction, and consequently the remaining one to any suitable direction. Don't shift the origin. let the Rotation matrix be

[ -1 -1 1]

[1 -1 1]

[0 2 1]

• You can choose to add new symmetry operator or add new points in the next popup menu showing you are going to change the unit cell volume
• Unit cell changes to orthorhombic. Now remove symmetry and turn it into "triclinic"- interface angles are still 90 degrees.
• Copy the coordinates of atoms from edit>edit data> structural parameters, and paste into any suitable spreadsheet software (say Microsoft Excel). You might have some problem with copying from vesta. So alternatively you may save this tranformed data as a .cif file, open with a text editor and cut your needed portion , paste it to another .csv file, open with excel, use data tab (or you may use macros) to get rid of punctuation marks to convert column to data.
• Scale down all z coordinate of points by half.
• Now open Wurtzite.cif file, remove its symmetry (its z axis is usually by default, hexagonal, otherwise permute between the axes to align basal direction along z axis. If you know elementary matrices from linear algebra, you can easily swap the axes. better do it before symmetry removal)
• Similarly scale down each z coordinate data of wurtzite by half, and also add 0.5 to each of the z coordinates.
• You have data of "size" of half-unit cells of GaN and diamond unit cells. Compare their unit cell length along a.k.a direction (you know which coordinate is referring to cubic and which one hexagonal system, don't you?). Scale you two separate unit cell data . Also remember the relative size of two structures along their own two remaining linearly independent axes. the data manipulation features of Excel can come in handy. You have the rotation matrix of diamond cubic structure, so you can find out transformed unit cell parameters quite easily.
• Now merge the two scaled data into a single file (likely excel), export to .csv, reopen with a text editor and format the text like usual .cif file, and open with VESTA. More tediously, individually copy these processed coordinates to make a new crystal structure in VESTA.