Author Topic: Supercell calculation  (Read 3622 times)

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Offline Inaoton

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Supercell calculation
« on: June 10, 2017, 14:39 »
Hello sir
    How can i  find the equilibrium lattice constants of a unit cell from supercell calculation? Do i have to divide  by a scaling factor.? And what about the equilibrium volume of the unit cell?

Offline lknife

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Re: Supercell calculation
« Reply #1 on: June 10, 2017, 20:27 »
In my opinion, after geometry optimizing the supercell, you can get the equilibrium lattice constant by noticing how many times you repeated your unit cell in each direction. Also, it's a good idea to optimize the geometry with the smallest unit cell. In addition, the lattice constants are different if you choose different unit cell with different symmetry.

Offline Inaoton

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Re: Supercell calculation
« Reply #2 on: June 12, 2017, 08:43 »
Thanks a lot .
1)But if i am supposed to model a structure with vacancy/vacancies, can i get a perfect model of the structure with the primitive cell where i delete atom/atoms?
                  Or
do i have to repeat the primitive cell and use substitutional alloy method or VCA (for a good model)?
2)Besides this, if the concerned structure is having a structure with fcc configuration(a=b=c), and if i repeat the cell by 2X2X1, the lattice constant so obtained do i need to scale the resultant lattice constant (after optimizing the geometry) by 1 or  2 to get the equilibrium lattice constant of the unit cell?

Offline Petr Khomyakov

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Re: Supercell calculation
« Reply #3 on: June 12, 2017, 13:06 »
You may first calculate the lattice parameters of the perfect crystal for the primitive cell.

For defect calculations, you can then build a supercell by repeating the primitive or conventional unit cell of the perfect crystal with the lattice parameters obtained in the first step. 

Afterwards, you can create a defect(s) in the supercell structure, and do ion relaxation of this created structure with a defect(s).

So, this is how you may model a crystal structure with a defect(s).