[QE-users] can i use this trick to do faster MD calculation using pw.x ?

[Jayraj Anadani]

Thank you Nicola sir for your reply, and sorry for repeating the message.

Actually, I am trying to obtain the metallic glass configuration through
AIMD using the pw.x code. My system has 128 atoms of Zr and Cu.

   - *VASP procedure:* first melted at 3000K using a nose thermostat up to
   5 picoseconds, then quenched at a high cooling rate of 10e13 K/s and
   reached 300K temperature.
   - *For the Quantum Espresso procedure,* I already used the cp.x code
   with the nose-hoover thermostat, but due to the metallic nature of Zr and
   Cu, I couldn't control the electron's adiabaticity. and if I perform the CG
   method in cp.x code, that will take too much time because of my
   computational limitations. So I prefer MD simulation using pw.x with
   "david" diagonalization. As the nose thermostat is not available in pw. x
   code, so I am using a "rescaling" thermostat for melting and "reduce-T" for
   quenching. However, the temperature fluctuations are too high compared to
   the other literature.

regards
jayraj

On Wed, 18 Oct, 2023, 5:41 pm Nicola Marzari via users, <
users at lists.quantum-espresso.org> wrote:

>
> Hi Jayraj,
>
> you wrote several times, but probably many did not know where to start -
> because you are addressing several complex problems without seeming to
> have much background in the field. Answers to your 3 points:
>
> 1) you will not get anything meaningul with the low cutoffs you suggest,
> just random stuff. use the minimum cutoffs suggested in my point 2) here
> below.
>
> 2) not sure - pseudopotentials are like people, they can be messed up
> deep inside. use the SSSP 1.3 efficiency:
> https://www.materialscloud.org/discover/sssp/table/efficiency
>
> 3) not sure where to start - you need to learn and understand MD - a
> good start is if you google "ercolessi md primer"
>
>                         nicola
>
>
>
>
> On 18/10/2023 11:18, Jayraj Anadani wrote:
> > Hello, QE community!
> > On my metallic system, which has 128 atoms, I am running AIMD
> > calculations using the pw.x code. Two pseudopotentials, PAW and USPP,
> > were each tested individually. I have the following queries:
> >
> >  1. For a faster AIMD calculation at a specific temperature, *Can I
> >     perform the whole simulation with a very low "ecutwfc" and
> >     "conv_thr" (i.e. ecutwfc=5 or 10) below a minimum cutoff of
> >     pseudopotential? *So that I can get the next ionic position very
> >     quickly with a fast scf cycle, then at the last MD step I will
> >     perform a single point energy (SCF) calculation with high "ecutwfc"
> >     and "conv_thr" to maintain a good amount of accuracy.
> >  2. Compared to PAW pseudopotential, USPP's convergence occurs *much
> >     more quickly. why*? (when ecutwfc is 25)
> >  3. The temperature fluctuation is incredibly small and nearly equal in
> >     the MD simulation of thousands of atoms in LAMMPS at a specific
> >     temperature (i.e., 1000K). However, the temperature fluctuation in
> >     MD with pw.x (AIMD) is significant, so we must set "tolp" which
> >     stands for tolerance for velocity rescaling. Although the average
> >     temperature is kept constant, *how closely does this significant
> >     fluctuation match the LAMMPS MD simulation?*
> >
> > Thank you
> >
> > regards
> > JAYRAJ ANADANI
> > Department of Physics
> > SPU Research scholar
> >
> > _______________________________________________
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>
> --
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
> Director, National Centre for Competence in Research NCCR MARVEL, SNSF
> Head, Laboratory for Materials Simulations, Paul Scherrer Institut
> Contact info and websites at http://theossrv1.epfl.ch/Main/Contact
>
> _______________________________________________
> 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)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
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