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

[Alathea Davies]

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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