[QE-users] a silly question to set the volume of the unit cell

[Rita Maji]

Hi,
Both way it should work, as you mentioned above. You can check the volume
in your output files.

Thanks,
Rita

Rita Maji
Research scholar
School of Physical Sciences
National Institute of Science Education and Research
Bhubaneswar, 752050
Odisha, India


On Fri, Apr 3, 2020 at 4:38 PM rekha sharma <rekha1997jpr at gmail.com> wrote:

> Dear All,
>
> Hope you are healthy during this hard time of COVID-19.
>
> I want to do some scf calculations at a slightly larger volume and smaller
> volume than the equilibrium volume  to compute gruneisen parameter.
> I tried with two different approaches to calculate the volume and  for
> both the cases my celldm's are different.
> I am seeking your expert guidance to choose the approach which is correct
> one.
>
> My system is with ibrav=-12 where the QE.in file adopts below geometry.
> ...
> &SYSTEM
>   ecutrho =   560
>   ecutwfc =   70
>   ibrav = 0
>   nat = 20
>   ntyp = 3
> /
> ...
> CELL_PARAMETERS angstrom
>    6.962369043   0.000000000  -0.001331115 (This 0.001331115 is deviated
> after vc-relax)
>    0.000000000   7.866710453   0.000000000
>   -6.770669758   0.000000000   9.932067578
>
>
> In one of the approach I used celldm(1)=  1.870829, 1.88973, 1.908623
> [converted values of 0.99, 1, 1.01 in Bohr] for minus, orig and plus volume
> deviation whereas I kept  my cell parameters as such as above
>
> In this case the celldm's are
>                        Minus                     original
>  Plus
> celldm(1)=   18.5821709383,   18.7699067564,    18.9575631139
> celldm(2)=    0.7920102607,     0.7920102607,     0.7920102607
> celldm(3)=    0.7009623470,     0.7009623470,     0.7009623470
> celldm(5)=    0.0191088849,     0.0191088849,    0.0191088849
> In this case celldm's 2,3,5 are same.
>
> while in other case I changes Crystal lattice vectors V1 only by +/-1%
> without defining celldm under &SYSTEM
> In this case my celldm's are
>                       minus 1%              Orig
>  Plus 1%
> celldm(1)=   18.7677900578,  18.7698683460,   18.7728685334
> celldm(2)=    0.7920979656,    0.7920102607,     0.7918836856
> celldm(3)=    0.6940295700,     0.7009623470,    0.7078588256
> celldm(5)=    0.0120986705,    0.0191088849,     0.0261162263
> here celldm's 2,3,5 are different and celldm(1) is different than I have
> in the case 1st.
>
> Can you please guide me how to set my volume at slightly larger volume
> and smaller volume than the equilibrium volume ?
> Your help will be very helpful for me and I will be grateful to you all.
>
> Thank you very much in advance.
>
> Best wishes
>
> Ms. Rekha
> Teaching Assistant,
> Department of Physics
> RK college, Jaipur, India
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