Re: [QE-users] What to modify in "dynamics_module.f90" for making constant zero pressure during NVT simulation(pw.x)

2024-03-16 Thread Jayraj Anadani 
Hello Paulatto,
I am doing MD calculation using pw.x.
first i melt my system at high temperature and then using "reduce-T"
option, i am quenching the system. But during quenching my pressure
fluctuates largely (as i mentioned). This is can be done under NVT ensemble.
If i will use NPT ( cell_dynamics) then i can't use "reduce-T" option and i
couldn't quench the system.
I just want to make zero pressure oscillation during md calculation by
setting ion_temperature=reduce-T option. And i am varying temperature from
1000 K to 900 K to 800 K upto room temperature 300K.

I hope i make it clear.

Thanks

Regard
On Sat, 16 Mar, 2024, 6:26 pm Lorenzo Paulatto, 
wrote:

>
> On 16/03/2024 12:17, Jayraj Anadani wrote:
>
> hello Paulatto,
> but in cell_dynamics all options for pressure control are for vc-md and
> vc-relax. and i want to control pressure during ion_temperature=reduce-T
> option.
>
> Dear Jayraj,
>
> it is not very clear what you want to do. You can have constant NVT, or
> NVE or NPT, or NPE. But it looks to me that you want constant instantaneous
> P and V, which is impossible as P is a macroscopic quantity, it only makes
> sense on average.
>
> kind regards
>
>
>
> ___
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Re: [QE-users] What to modify in "dynamics_module.f90" for making constant zero pressure during NVT simulation(pw.x)

2024-03-16 Thread Stefano de Gironcoli 

Dear Jayraj,

adding to what Lorenzo already replied, P and V as well as E and T are 
conjugated quantities: if you fix one the other fluctuates (of an amount 
\propto 1/sqrt N that vanishes in the thermodynamic limit).


so you can have NVE simulations where the average kinetic energy is 
related to the system temperature but fluctuates in time, or using a 
thermostat you can fix the system temperature (sampling NVT ensemble) 
but you give up energy conservation.


the same for V and P, you can have NVT and NPT, or NVE and NPH (because 
the conserved quantity is in this case the enthalpy). The larger the 
system the smaller the fluctuations but for finite number of particles 
the fluctuations are always present (and the thermostats and barostats 
do have their own degrees of freedom whose contribution become 
negligible in the thermodynamic limit).


stefano

On 16/03/24 13:56, Lorenzo Paulatto wrote:

On 16/03/2024 12:17, Jayraj Anadani wrote:

hello Paulatto,
but in cell_dynamics all options for pressure control are for vc-md 
and vc-relax. and i want to control pressure during 
ion_temperature=reduce-T option.


Dear Jayraj,

it is not very clear what you want to do. You can have constant NVT, 
or NVE or NPT, or NPE. But it looks to me that you want constant 
instantaneous P and V, which is impossible as P is a macroscopic 
quantity, it only makes sense on average.


kind regards




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IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
23-24/423 B115, 4 place Jussieu 75252 Paris CX 05

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Re: [QE-users] What to modify in "dynamics_module.f90" for making constant zero pressure during NVT simulation(pw.x)

2024-03-16 Thread Lorenzo Paulatto 


On 16/03/2024 12:17, Jayraj Anadani wrote:

hello Paulatto,
but in cell_dynamics all options for pressure control are for vc-md 
and vc-relax. and i want to control pressure during 
ion_temperature=reduce-T option.


Dear Jayraj,

it is not very clear what you want to do. You can have constant NVT, or 
NVE or NPT, or NPE. But it looks to me that you want constant 
instantaneous P and V, which is impossible as P is a macroscopic 
quantity, it only makes sense on average.


kind regards




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IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
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Re: [QE-users] What to modify in "dynamics_module.f90" for making constant zero pressure during NVT simulation(pw.x)

2024-03-16 Thread Kazume NISHIDATE 
Dear Anadani,

> I am performing an AIMD simulation of metallic alloys and
>  encountering huge pressure(~50 to -50 Kbar) fluctuations,

It may be normal depending on how many atoms you are using in your
system.

In MD simulation, temperature and pressure are measured in ensemble
average. If you do not have enough atoms in your system, say under 100
atoms, you must 'average' physical/chemical quantities over many time
steps. This is the Ergodic theorem.



> 2024/03/16 20:17、Jayraj Anadani のメール:
> 
> hello Paulatto,
> but in cell_dynamics all options for pressure control are for vc-md and 
> vc-relax. and i want to control pressure during ion_temperature=reduce-T 
> option.
> ___
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> ___
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
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西館数芽
Kazume NISHIDATE Ph.D

Department of Systems Innovation Engineering,
Graduate School of Science and Engineering, Iwate University
4-3-5 Ueda, Morioka, Iwate, 020-8551 JAPAN
Phone:+81-19-621-6391
kazume.nishid...@gmail.com, nisid...@iwate-u.ac.jp
https://sites.google.com/site/nisidatelab/

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Re: [QE-users] What to modify in "dynamics_module.f90" for making constant zero pressure during NVT simulation(pw.x)

2024-03-16 Thread Jayraj Anadani 
hello Paulatto,
but in cell_dynamics all options for pressure control are for vc-md and
vc-relax. and i want to control pressure during ion_temperature=reduce-T
option.
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Re: [QE-users] What to modify in "dynamics_module.f90" for making constant zero pressure during NVT simulation(pw.x)

2024-03-16 Thread Lorenzo Paulatto 
Dear Anadani,
Check the cell_dynamics input variable and related. 



Kind regards.



On March 16, 2024 10:51:01 AM GMT+01:00, Jayraj Anadani 
 wrote:
>Hello QE community,
>I am performing an AIMD simulation of metallic alloys and encountering huge
>pressure(~50 to -50 Kbar) fluctuations, i wanted to set pressure around
>zero during NVT simulations with temperature reduction(reduce -T)or
>rescaling. Currently, I'm manually adjusting the box size after each
>certain MD steps (nstep-200) to fix this. Is there an automated way to
>maintain constant zero pressure?  The barasat is available for NPT
>simulation but i am using "reduce -T" option so i can't do NPT simulation
>way.
>Or i can change some part of script in "dynamics_module.f90".
>
>Thanks
>Regards
>
>Jayraj Anadani
>SPU Research scholar
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