[ase-users] Units for setting initial velocities

[Caro Miguel]

Hi Jakob,

Thanks a lot for your answer. My system is already equilibrated, I just want to continue the dynamics with ASE from there at the same T, so hopefully the NPT class will be able to do that.

Thanks again,
Miguel

--
Dr. Miguel Caro
Postdoctoral researcher
Department of Electrical Engineering and Automation, and
COMP Centre of Excellence in Computational Nanoscience
Aalto University, Finland
Email: mcaroba at gmail.com
Work: miguel.caro at aalto.fi
Website: http://mcaroba.dyndns.org
________________________________________
From: Jakob Schiøtz <schiotz at fysik.dtu.dk>
Sent: 15 April 2017 01:46
To: Caro Miguel
Cc: ase-users at listserv.fysik.dtu.dk
Subject: Re: [ase-users] Units for setting initial velocities

> On 14 Apr 2017, at 8:43, Caro Miguel via ase-users <ase-users at listserv.fysik.dtu.dk> wrote:
>
> Hi all,
>
> I want to run MD with the NPT class. I would like to set initial velocities for my system with the set_velocities() method of the Atoms class. Which are the units that ASE is expecting?

The unit that corresponds to distances being Å, energy being in eV and mass in units.  It is going to be a silly unit, unfortunately.

>
> Also, the documentation on the NPT class says that it expects temperatures in eV. Is this a typo, or should one pass 3/2 k_B T in eV instead of the temperature in K?

No, that is not a typo - ASE is very inconsistent with temperature units for MD, fixing it is on my to-do list.  But you should give k_B * T, do *NOT* multiply with 3/2.

Also, be aware that NPT dynamics is good at maintaining a constant temperature, but less good at getting there if the temperature is different.  Look for oscillations in the temperature!  You may want to use NPT_Berendsen to initialize the system, and then switch to NPT.

Best regards

Jakob


>
> Many thanks,
> Miguel
>
> --
> Dr. Miguel Caro
> Postdoctoral researcher
> Department of Electrical Engineering and Automation, and
> COMP Centre of Excellence in Computational Nanoscience
> Aalto University, Finland
> Email: mcaroba at gmail.com
> Work: miguel.caro at aalto.fi
> Website: http://mcaroba.dyndns.org
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> ase-users mailing list
> ase-users at listserv.fysik.dtu.dk
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--
Jakob Schiøtz, professor, Ph.D.
Department of Physics
Technical University of Denmark
DK-2800 Kongens Lyngby, Denmark
http://www.fysik.dtu.dk/~schiotz/