How to creat input files for a supercell

[baolkvn]

Dear all VASP users,
I have read many previous posts about supercell. Therefore I have litlte knowledge on Supercell, such as duplicate 1 premitive cell to MxLxN, or take a look Dr.Furthmuller webpage for supercell.F,...etc However I am still in some troubles:

1. Don`t know to to use supercell.F file to create input files for my projects.

2. I wonder if we can create input files for supercell manually. If yes, how do we define parameters, coordinators in POSCAR, KPOINTS file? Please help me with an example.

Thank you very much.
And sorry if I have a dump question.

TA Quoc Bao
University of Technology - HCM City-Vietnam

[admin]

1) please contact Dr. Furthmüller
2) of course:
POSCAR
-- Bravais Matrix:
please multiply the lattice vectors by the factors L, M and N if you want to generate a LxMxN supercell
then generate the positions of the atoms in the supercell by adding the translational vectors of the original primitive cell (input in carthesian coordinates) or add the replica of the primitive cell (input in direct coordinates) to generate all positions in the supercell.
to give you a short example to generate a 2x2x1 supercell of a simple cubic lattice with 1 atom per primitive cell, a=2.0 Ã…:
--: simple lattice:
primitive cubic cell
1.0
2.0 0.0 0.0
0.0 2.0 0.0
0.0 0.0 2.0
1 (1 atom per cell)
Carthesian
0.0 0.0 0.0

--: 2x2x1 supercell, carthesian coordinates
2x2x1 supercell (now tetragonal) a',b'(=a'),c'(=a)
1.0
4.0 0.0 0.0 #(the a lattice parameter has been doubled,--> a')
0.0 4.0 0.0 #(the b lattice parameter has been doubled --> b')
0.0 0.0 2.0 #(c has been kept for the 2x2x1 supercell)
4 #(4 atoms in the supercell)
Carthesian
0.0 0.0 0.0
2.0 0.0 0.0 # ( = +(a,0,0) with respect to the primitive cell )
0.0 2.0 0.0 # ( = +(0,b,0) )
2.0 2.0 0.0 # ( = +(a,b,0) )

2x2x1 supercell, direct coordinates
2x2x1 supercell (now tetragonal)
1.0
4.0 0.0 0.0 # a' 0 0
0.0 4.0 0.0 # 0 b' 0
0.0 0.0 2.0 # 0 0 c'=a
4
Direct
0.0 0.0 0.0
0.5 0.0 0.0 (atom +(a,0,0) is at position (1/2*a', 0, 0 )
0.0 0.5 0.0
0.5 0.5 0.0

KPOINTS file
to keep the same density of k-points in reciprocal space, the number of k-points has to be rescaled with 1/N along those directions which have been multiplied by N to generate the supercell
eg, if you have a 12x12x12 k-mesh for the primitive cell, you need a 6x6x12 mesh for the 2x2x1 supercell.

[baolkvn]

Thank you very much, admin. I've got it.