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

[Nicola Marzari]

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