[CP2K-user] [CP2K:15338] Ar lattice constant calculation

[sumit agrawal]

Dear Lucas Lodeiro and Fabian,

Thanks for your nice suggestions. I am new to cp2k. I have just
started learning this. I have some query regarding my procedure for
preparation for crystal structure. I am following below procedure to
prepare the crystal structure:

First, I have prepared the crystal structure (2x2x2) with the lattice
dimension a=5.2229 A, b=5.2229 A and c=5.2229 A. It contains 63 atoms.
After that I removed some atoms from x, y and z directions so that it
become periodic in x, y and z direction. After this, it contains 32 atoms.
Now I save this lattice in XYZ format. This will be my
initial coordinate system. Am I correct?

After this I took this coordinate file and ran for the cp2k calculation.

Now in cp2k calculations for this lattice structure what will be my cube
size? (Here you mention it will not be 20 A. )

One more query, here I am starting with a lattice dimension with 5.2229 A .
So after Cell_OPTIMIZATION, will the geometry of my crystal change or not?

Yes, dispersion correction must be required for this type of calculation, I
will do that.

Here I am attaching my crystal structure images.



Thanks
Sumit



On Tue, May 11, 2021 at 11:02 PM Lucas Lodeiro <eluni... at gmail.com>
wrote:

> Hi Sumit,
>
> First of all, you cannot find the lattice constant with this type of
> calculation. You ran an ENERGY calculation. If you want to do it, you need
> to run a CELL_OPT calculation.
> In your current calculation, you use a 20 A lattice constant cube. Also, I
> think your initial cell dimension is not correct, since the lattice
> constant of Argon is 5.26 A, then a 2x2x2 supercell is not 20 A sized.
> Also, your system has 63 atoms... ¿?.
>
> Other related topics are: a 2x2x2 supercell is not sufficient to compute a
> periodical Argon system... You need a bigger supercell, or use kpoints.
> Also, as this system just interacts by dispersion, probably the PBE
> functional is not sufficient at all. You need to account the dispersion
> terms by means of Grimes D3 or other.
>
> Regards
>
> El mar, 11 may 2021 a las 14:08, sumit agrawal (<sumitag... at gmail.com>)
> escribió:
>
>> Hii everyone,
>>
>> I want to calculate a lattice constant for the Ar crystal of (2*2*2 unit
>> cell). I am attaching my input and out files. Where I will find the
>> lattice constant ?
>>
>> Please help me!!
>>
>>
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