[DFTB-Plus-User] NEMD MD with DFTB+

[Bálint Aradi]

Dear Ali,

indeed, you can only apply isotropic pressure in DFTB+. And yes, the 
non-equilibrium transport (via Greens functions) refers to the 
electronic system (e.g. when you apply bias to your systems via 
contacts), so this is not what you are looking for.

Unfortunately, I am definitely not an MD expert, so I am not sure, what 
would be the right way to simulate you system.

Best regards,

Bálint

On 17.06.22 17:53, Alathea Davies wrote:
> Hello!
> 
> I am hoping to conduct desalination simulations utilizing the MD 
> functionality of DFTB+. I've been able to look at self diffusion between 
> water, NaCl, and my membranes, and what I would like to do next is to 
> apply a pressure difference in my simulation cell to simulate 
> desalination. This would require setting the pressure at one end of my 
> simulation cell different from the pressure at the other end. My 
> intention is to apply pressure in the z-direction and periodic boundary 
> conditions in both x- and y-. However, it doesn't seem that I would be 
> able to do this with DFTB+. My understanding is that I can only define 
> one external pressure around my entire periodic system, rather than 
> defining different pressures at different boundaries. I've been reading 
> through the manual extensively and searching online, but I can't come to 
> a conclusive answer whether I'd be able to perform these simulations or 
> if there is a work-around to do this with DFTB+. My two questions, then, 
> are:
> 
>  1. Does DFTB+ do non-equilibrium MD? Would other users have suggestions
>     how I could perform these calculations with DFTB+?
> 
>  2. I understand that DFTB+ has the "Transport" calculations, but from
>     my understanding in the manual, these are more quantum mechanics
>     based transport (electrons, phonons, etc.) then mass transport. Am I
>     understanding this correctly? 
> 
> If there are any suggestions regarding how I could use DFTB+ MD 
> functionality to conduct pressure-driven desalination simulations, I 
> would be very grateful to hear them!
> 
> Thank you so much for your help!
> 
> ~ Alathea (Ali) Davies
> 
> 
> Graduate Research Assistant
> Computational Design Research Group
> University of Wyoming
> Department of Chemistry
> adavies2 at uwyo.edu
> 
> 
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-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b-aradi/

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