[QE-users] Energy calculation

[Premkumar Thirumalaisamy]

Hi,
    Always compare the energy per formula unit, if you do that in your case
there is a small different in energy which may be due to different k-grid
and energy cutoff.
   I think it is better to optimize the kpoints and energy cutoff for
particular unit cell or supercell.

On Sun, Jan 19, 2020 at 2:55 AM Manu Hegde <mhegde at sfu.ca> wrote:

> Hi Pooja,
> I think CaO is a cubic crystal. You can use VESTA to generate a supercell.
> It can take .cif file. Play with it. I believe extending lattice
> parameter 2X2X2 generate a 36 atom supercell.
> HTH
> Manu
> (McMaster University)
>
> On Sat, Jan 18, 2020 at 12:38 AM Pooja Vyas <poojavyas1251995 at gmail.com>
> wrote:
>
>> Respected sir/madam,
>> Referring a paper on calculation of energy with vacancy in CaO, I want to
>> re-calculate the energy with the same number of atoms used in the paper.
>> They have 36 atoms in their supercell, 3 x 3 x 2 monk horst pack grid.
>> From this information, is it possible to know what could be the value of n,
>> in n x n x n supercell and what could be the initial number of atomic
>> positions defined?
>>
>> On Thu, Jan 16, 2020 at 11:58 AM Laurent Pizzagalli <
>> laurent.pizzagalli at univ-poitiers.fr> wrote:
>>
>>> Well, maybe because in your first calculation you had two atoms, and 64
>>> in the second one.....You should try to see if multiplying -107.10 by 64/2
>>> improve the comparison....
>>>
>>> L.
>>>
>>> On 16/01/2020 06:23, Pooja Vyas wrote:
>>>
>>> Initially I had run my input script with ecut=100Ry and k-points= 11 11
>>> 11 1 1 1. At that time my energy was -107.10Ry. During this run, I had
>>> specified only two atomic positions (Ca: 0 0 0, O: 0.5 0.5 0.5)
>>> For the same system but with ecut=60Ry and k-points= 3 3 3 1 1 1 the
>>> calculated energy was -3427.40Ry. During this run, I had specified 64
>>> atomic positions.
>>> Why does total energy value vary so much?
>>>
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-- 
Regards,
Premkumar Thirumalaisamy,
Research Scholar, Department of Medical Physics,
Anna University, Chennai, India - 600025.
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