[QE-users] Question on excess electron localization and structural rearrangement in PEDOT:PSS

[施潇虎]

施潇虎
2717984661 at qq.com

BNU



Dear QE users,

 

I am currently thinking about a computational problem related to the conductivity enhancement mechanism of PEDOT, and I would greatly appreciate any comments on whether this modeling strategy is reasonable, as well as suggestions on possible methods. I also hope to keep the calculations as simple as possible, since I am trying to finish my degree.

 

The physical process I am interested in is the following: I do not consider how external excitation injects electrons into the polymer, but only focus on what happens after extra electrons have already entered the PEDOT system. My working hypothesis is that the electrons preferentially move along PEDOT-rich regions in the polymer and then become locally accumulated near PSS, which in turn induces local structural and/or chemical changes in regions that were originally insulating, eventually forming more stable low-resistance conduction pathways. After the external excitation is removed, part of these pathways may remain, leading to an overall increase in the conductivity of the film.

 

I recently started learning DFT calculations and can now perform some common electronic-structure calculations. After discussing with ChatGPT, I tried to break this problem down into the following sub-questions:

 

1.Where do the extra electrons preferentially localize in the PEDOT/PSS composite system?

2.Can the region near PSS act as an electron trap or exhibit significant local polarization?

3.Can the extra electrons reduce the energy barrier for certain local structural rearrangements, for example:

(a) local rearrangement of PSS;

(b) reduced PEDOT-PEDOT distance and enhanced contact;

(c) transformation of a charge-transport pathway originally blocked by PSS into a more continuous low-resistance pathway?

4.After removing the extra electrons, can such structural changes remain metastable, thus explaining why the conductivity enhancement persists after the excitation is turned off?

 

If convenient, I would be very grateful for any suggestions on whether this problem decomposition, model selection, and computational route are reasonable. I would also sincerely welcome any direct criticism of aspects that may be physically or computationally inappropriate, since I would like to define the problem as clearly as possible before starting and avoid spending too much time on ineffective calculations.

 

At the same time, I also have several specific questions:

 

1.Is it reasonable to use PBEsol for this kind of problem, or would other functionals be more appropriate? More generally, would a standard GGA functional tend to over-delocalize the extra electrons?

 

2.So far, I have learned basic relaxation, band structure, and DOS calculations. What additional knowledge or techniques would I need in order to study this problem properly?

 

3.Since PEDOT:PSS systems are typically on the scale of tens of nanometers, should I use oligomer models or periodic polymer-chain models?

 

4.If a periodic model is adopted, what kind of minimal representative structure should be considered first: an ordered PEDOT/PSS interfacial model, a statistical model of disordered chain segments, or local configurations extracted from classical MD and then studied by DFT?

 

5.In a PEDOT:PSS system, is it necessary to explicitly consider spin polarization, especially when adding extra electrons?

 

6.If my main concern is whether the presence of extra electrons makes local structural rearrangements easier, would static DFT already be enough, or should I further consider more advanced approaches?

 

7.If the goal is to study whether the conduction pathway remains after removing the extra electrons, is it sufficient to optimize the charged state first and then re-optimize the neutral state, or would barrier calculations / free-energy analysis be necessary to demonstrate a truly metastable state?

 

8.If I eventually want to connect the calculations with “conductivity enhancement,” would it be enough to compare DOS, band gap, and charge-density changes, or would I need more direct indicators of transport capability?

 

9.If I were allowed to do only one minimum viable test, which model and which result would be the most informative for deciding whether this idea is worth pursuing?

 

10.If the goal is not to reproduce the entire process in full detail, but only to support the conclusion that “extra electrons can induce local rearrangement and enhance conductivity,” which calculations would you recommend prioritizing, and which ones could reasonably be omitted?

 

Any suggestions would be greatly appreciated. Thank you very much for your time.
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