Background / theory: The electron transfer in organic materials was formalized by the Marcus theory, introducing $|H_{ab}|$ to describe the how molecules (or more generally: sites) are coupled with each other, and reorganization energy $\lambda$, about how costly it is to to accommodate a charge after the carrier moved. Especially if the atomic coordinates of the material already are known, it is possible to access these parameters by quantum chemical calculations.

Background / software: NWChem seems to be one of the freely available programs allowing such an additional characterization. New to this program, I found both the standard entry in the manual (here), as well as a post in the user forum (here) by 2012, comparing the result to a literature reference in Phys Rev B 2007 as "work[ing] pretty well". It is possible for me to to replicate the computation filed there under "Sep 19th 2012", too.

The feeling: It seems dangerously simple to use this script for an other structure, just replacing the first / second / third block of coordinates by the $(x,y,z)$ extracted from X-ray diffraction analyses about molecule A, hoovering neighbor B, and the close couple / dimer (AB). Indeed, my first tests (again, as a beginner) failed; the program launched, yet eventually shut down -- likely because I do not know well enough how to proceed.

The question: Does one of you know about an additional tutorial, starting from accessible atom coordinates of molecular materials, concluding with the Marcus parameters of the electron hopping?

  • $\begingroup$ I'm not entirely sure what you're asking. It sounds like you want to run a particular NWChem calculation, but change the coordinates. If so, it would help to know the specific errors you're getting, rather than just 'eventually shut down.' $\endgroup$ Jul 16, 2019 at 20:04
  • $\begingroup$ There's also an NWChem forum, which may be helpful: nwchem-sw.org/index.php/Special:AWCforum $\endgroup$ Jul 16, 2019 at 20:05
  • $\begingroup$ @GeoffHutchison Yes I would like to use NWChem to determine Marcus parameters, eventually with coordinates about other materials. Like as the post by "St" (Oct 25th 2015) I was wondering about the large coupling (0.92 eV) even if the antracenes in the preceedingly post form a sandwich, only 3 \AA apart from each other. Other typical organic electronics e.g., the better polymorph of rubrenes are reported just around 0.1..0.2 eV (with far less superposition, of course). So it still is a search for «more realistic» coordinates, with partial overlap of the $\pi$-systems only and determined MPs. $\endgroup$
    – Buttonwood
    Jul 16, 2019 at 20:49
  • $\begingroup$ @GeoffHutchison As I recall, many, yet not all «shut downs» were caused by input errors of mine -- which anyway I'll check again tomorrow, and I already deposit a question in their forum prior to ChemSE, too. $\endgroup$
    – Buttonwood
    Jul 16, 2019 at 20:51


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.