[CP2K-user] [CP2K:15344] Ar lattice constant calculation

[sumit agrawal]

Thanks Fabian!!!

>From the output file I can see a=b=c=11.0732 A. Is the lattice constant
11.0732 A or half of this which is 5.5366 A, since it is a 2x2x2 unit cell ?


On Wed, May 12, 2021 at 6:14 PM Fabian Ducry <fabia... at gmail.com> wrote:

> cp2k prints "CELL| Vector" after each iteration of the optimizer. From
> this you can calculate the lattice constant.
>
> The lattice constant usually refers to the dimension of a unit cell,
> therefore it does not change when you create a supercell. The cell
> dimensions, however, differ between the unit and supercell.
>
> Fabian
> On 12.05.2021 13:42, sumit agrawal wrote:
>
> Dear Fabian,
>
> Thanks for the quick response. Actually I prepared a lattice structure
> (2x2x2) in VESTA software. Is it the correct tool to prepare lattice
> structure, any idea?
>
> I tried again to prepare a lattice structure. So 2x2x2 will contain 32
> atoms. Then I performed cell_opt in cp2k. I am attaching my coordinate
> file, input file and out file.
>
> Where will I find the lattice constant in the output file?
>
> One more query: will the lattice constant for 1x1x1 unit cell and nxnxn
> unit cell be same or different?
>
>
>
>
>
> On Wed, May 12, 2021 at 1:57 PM Fabian Ducry <fabia... at gmail.com>
> wrote:
>
>> Dear Sumit
>>
>> A supercell of (2x2x2) has to contain 2*2*2=8 times the number of atoms
>> of the unit cell. So It can never have an odd number as in your case 63.
>> You should follow a tutorial on how to prepare such a structure, e.g. with
>> ASE. Here, for example, you find instruction on how to build a crystal:
>> http://exciting-code.org/lithium-atomic-simulation-environment. Once you
>> have the ASE Atoms object building the supercell is as easy as
>> atoms*(2,2,2). When you have a correct crystal, make sure that the &CELL
>> section in the cp2k input matches the lattice dimensions of the crystal.
>> You cannot just use an arbitrary number.
>>
>> CELL_OPT will optimize both the atom positions as well as the lattice
>> dimensions.
>>
>> Fabian
>> On 12.05.2021 06:19, sumit agrawal wrote:
>>
>>
>> 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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