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

[rekha sharma]

Thank you Sir/Madam,
It worked for me. I have changed all cell vectors by +/-1%.
 How I can estimate the %change in the volume?  Or I should ask if I change
all cell vectors by +/-1% then how the volume will change based on these
new parameters for monoclinic structure? I see volume is changes by around
2-3%. for moclinic case the V is calculated by a*b*c*sin(beta). But I am
not able to get this volume value from the QE.in file?
Could you please elaborate it?

-1%

bravais-lattice index = 0

lattice parameter (alat) = 11.5206 a.u.

unit-cell volume = 4358.0284 (a.u.)^3

crystal axes: (cart. coord. in units of alat)

a(1) = ( 1.000000 0.000000 0.000000 )

a(2) = ( -0.471829 1.069357 0.000000 )

a(3) = ( 0.000000 0.000000 2.665261 )

0%

bravais-lattice index = 0

lattice parameter (alat) = 11.6370 a.u.

unit-cell volume = 4491.4283 (a.u.)^3

crystal axes: (cart. coord. in units of alat)

a(1) = ( 1.000000 0.000000 0.000000 )

a(2) = ( -0.471829 1.069357 0.000000 )

a(3) = ( 0.000000 0.000000 2.665261 )

1%

bravais-lattice index = 0

lattice parameter (alat) = 11.7534 a.u.

unit-cell volume = 4627.5231 (a.u.)^3

crystal axes: (cart. coord. in units of alat)

a(1) = ( 1.000000 0.000000 0.000000 )

a(2) = ( -0.471829 1.069357 0.000000 )

a(3) = ( 0.000000 0.000000 2.665261 )

Once again, thank you very much for giving time to my query.
I hope for consistent help in future also.

Best Wishes,

Ms. Rekha

On Sat, Apr 4, 2020 at 5:43 PM Rita Maji <rita.maji at niser.ac.in> wrote:

> 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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-- 




Best wishes

Ms. Rekha
Teaching Assistant,
Department of Physics
RK college, Jaipur, India
Mob.: +11 90-95 790 71 697
Email: rekha1997jpr at gmail.com
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