[Pw_forum] System Relaxation Containing Charged_molcule

[Oliviero Andreussi]

Dear Abir Shadman,

For the first question, my understanding (but others are more knowledgeable than me) you can use tot_charge to specify that the total charge of your system is the one of your phosphate molecule (say -2), but whether this charge goes all on the phosphate depends on the relative affinities of the different components of your system. Tot_charge only controls the total amount of electrons in your simulation, it does not enforce by itself where these electrons will go. For the same reason it cannot be used to model a sheet of charge placed above the NR. 

On the other hand, for this purpose one possible way (there might be others) would be to use the Environ module for QE (www.quantum-environ.org <http://www.quantum-environ.org/>). The new release of the module (which will come out later today or tomorrow) allows you to consider arbitrary fixed distributions of charges inside the simulation cell, thus also sheets of charges (but also wires or point-like charges). Whether this simulation converges, makes sense, is physical depends a lot on your system and set ups, but you can try playing with it. If you want to use the module and need help with the set up of the calculation, feel free to contact me. 

Best regards,

Oliviero Andreussi

> On 12 Jan 2016, at 22:52, Abir Shadman <abirshadman at gmail.com> wrote:
> 
> ​Thanks Dr. Paulatto for your reply. However about my first question, I am trying to relax a charged phosphate molecule (say doubly charged) over a MoS2 Nanoribbon. They are attracted together by van der waals force as reported in many papers. My question was how to do the bfgs relaxation considering the charged molecule? I can simulate a, say neutral phosphoric acid over the NR, but what I have to do incorporate the charge?
> 
> And about your reply to my second question, will tot_charge keyword consider a sheet charge over neutral NR? 
> 
> Thanks again. I look forward to hearing from you. It will be very helpful from me to get responses from other QE users also.
> 
> Best,
> 
> On Tue, Jan 12, 2016 at 4:40 AM, Abir Shadman <abirshadman at gmail.com <mailto:abirshadman at gmail.com>> wrote:
> Dear researchers,
> 
> I have 2 questions:
> 
> 1. I am trying to relax a charged phosphate molecule over a MoS2 Nanoribbon and then do scf and bands calculation. I am informed of the such simulations for neutral multilayered TMDCs. That's why, I basically need to know how to incorporate these negative charges in simulation?
> 
> 2. If I want to do bfgs,scf and bands simulation of a MoS2 NR with a sheet charge over it, will it be possible? How to consider sheet charge in QE?
> 
> I am relatively new to QE. I have done some basic simulations in QE. If these types of questions with charged molecules are already answered, can anyone atleast provide me those links/sources? 
> 
> Thanks in advance.
> 
> ​Best,
> Abir Shadman
> Dept. of EEE,BUET.
> 
> ᐧ
> 
> 
> 
> -- 
> Abir Shadman
> Dept. of EEE,BUET.
> 
> ᐧ
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