Can anyone please help me transform $\ce{LiCoO2}$ hexagonal cell ($a \times a \times c$) to orthorhombic cell ($a \times a \sqrt{3} \times 1$) and hexagonal cell ($a \sqrt{3} \times a \sqrt{3}\times 1$)?
2 Answers
structure 1
Method affine transformation of simulation box after replicating in X and Y in ovito
OUTPUT: POSCAR
POSCAR file written by OVITO
1.0
2.8428978920 0.0000000000 0.0000000000
0.0000000000 4.9240398407 0.0000000000
0.0000000000 0.0000000000 14.1456146240
Li Co O
6 6 12
Direct
0.000000000 0.000000000 0.000000000
0.500000461 0.166666663 0.333332985
0.000000000 0.333333809 0.666666981
-0.000000000 0.666667086 0.333332985
0.499999958 0.500000436 0.000000000
0.499999455 0.833334173 0.666666981
0.000000000 0.333333809 0.166666998
-0.000000000 -0.000000000 0.500000000
0.500000461 0.166666663 0.833333019
0.000000000 0.666667086 0.833333019
0.499999455 0.833334173 0.166666998
0.499999958 0.500000436 0.500000000
-0.000000000 -0.000000000 0.239586996
0.500000461 0.166666663 0.093745997
0.500000461 0.166666663 0.572920049
-0.000000000 0.333333809 0.427080019
-0.000000000 0.333333809 0.906254011
-0.000000000 -0.000000000 0.760412970
0.000000000 0.666667086 0.093745997
-0.000000000 0.666667086 0.572920049
0.499999958 0.500000436 0.239586996
0.499999455 0.833334173 0.427080019
0.499999455 0.833334173 0.906254011
0.499999958 0.500000436 0.760412970
structure2
Method affine transformation of simulation box after replicating in X and Y in ovito
OUTPUT: POSCAR
POSCAR file written by OVITO
1.0
4.9240450859 0.0000000000 0.0000000000
2.4620173651 4.2643450666 0.0000000000
0.0000000000 0.0000000000 14.1456146240
Li Co O
9 9 18
Direct
0.000000000 0.000000000 0.000000000
0.333333430 -0.000000000 0.333332985
-0.000000007 0.333333975 0.666666981
-0.000000018 0.666666944 0.333332985
0.666665892 -0.000000000 0.666666981
0.333333114 0.333333891 0.000000000
0.666666524 0.333333835 0.333332985
0.333332722 0.666667838 0.666666981
0.666666229 0.666667782 0.000000000
-0.000000007 0.333333975 0.166666998
-0.000000000 -0.000000000 0.500000000
0.333333430 -0.000000000 0.833333019
-0.000000018 0.666666944 0.833333019
0.666665892 -0.000000000 0.166666998
0.333332722 0.666667838 0.166666998
0.333333114 0.333333891 0.500000000
0.666666524 0.333333835 0.833333019
0.666666229 0.666667782 0.500000000
0.000000000 -0.000000000 0.239586996
0.333333430 -0.000000000 0.093745997
0.333333430 -0.000000000 0.572920049
-0.000000007 0.333333975 0.427080019
-0.000000007 0.333333975 0.906254011
-0.000000000 0.000000000 0.760412970
-0.000000018 0.666666944 0.093745997
-0.000000018 0.666666944 0.572920049
0.666665892 -0.000000000 0.427080019
0.666665892 -0.000000000 0.906254011
0.333333114 0.333333891 0.239586996
0.666666524 0.333333835 0.093745997
0.666666524 0.333333835 0.572920049
0.333332722 0.666667838 0.427080019
0.333332722 0.666667838 0.906254011
0.333333114 0.333333891 0.760412970
0.666666229 0.666667782 0.239586996
0.666666229 0.666667782 0.760412970
Load POSCAR > show periodic image > affine transformation > manual selection > delete selected atoms >export as POSCAR
NOTE: During delete of extra atom outside simulation box don't include periodically equivalent atoms in boundaries
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$\begingroup$ I just downloaded version 3.6 on my macbook and I could not find periodic image and manual selection $\endgroup$ Dec 22, 2021 at 0:40
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When you change the lattice, you actually change the crystal structure (don't confuse the lattice, a geometrical object, with the crystal structure, a real object).
First of all you have to consider the space group types of your starting and final structures and verify that a group-subgroup relationship holds between them. If yes, you can transform the structure.
Than you can use the tools avaliable at the Bilbao Crystallographic Server for transforming your structure. It is imperatuve that you use a correct transfomation matrix. At this point the Server will give you the atomic positions in the Wyckoff sites for the new space group. You can save this structure as a CIF file and import it in Vesta.
Edit -> Edit Data -> Unit cell
option? From there you can change the unit cell as far as I know. $\endgroup$