[QE-users] Energy calculation

[Pooja Vyas]

Thank you sir

On Tue, 21 Jan 2020, 11:52 am Premkumar Thirumalaisamy, <prem.unom at gmail.com>
wrote:

> 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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