Computing electronic couplings on a multilayer stack

Introduction

As electronic couplings are required for each type of pairs in the morphology, they need to be computed on morphologies that include all interfaces. We therefore use the periodically extended morphology of a reduced stack as input (i.e. a deposited stack containing all layers but with reduced thicknesses, see e.g. stack_structurePBC.cml in the ab-initio OLED stack tutorial. For single-layer simulations (e.g. for charge carrier mobility), simply provide the structurePBC.cml from Deposit.

Setup

  • General:
    • Morphology: stack_structurePBC.cml
    • Run QuantumPatch: True
    • QuantumPatch Type: Polarized
    • Calculate Js: enabled
    • Disable in-vacuo Lambda/EA/IP calculation
    • Disregard molecular states
  • Engines: For electronic couplings, BP86 is usually sufficient. Therefore, set the following engines (as usually, leave all settings not explicitly mentioned as is):
    • TM core: Engine: Turbomole, Fallback disabled, Functional: BP86, Basis: def2-SVP
    • DFTB+ 1: Engine: DFTB+, Fallback enabled, Fallback Engine: "TM core"
  • Shells:
    • Core shell: As we want to have molecules of all layers present, we can either go via list of molecules, or define an inner box such that just enough molecules (~150) of each species are present with sufficient environment. To validate which cutoff works, there is a tool named "GetNumberInnerMolsFromBox.py" in QuantumPatch/MolecularTools which prints you the number of molecules of each type for given cutoffs in x, y and z-direction and a given cml file. In our case values of 92.0A, 92.0A and 12.A for x-, y- and z-cutoff respectively resulted in 144 MeoTPD, 153 alpha-NPD, 46 Ir(piq)3 and 138 BPhen molecules present in the core box. There fore, set Inner Part Method to "Inner Box Cutoff" and supply these cutoffs. Note that for single layers, especially pristine systems, the definition of the core shell via "Number of molecules" (recommended: 100) is more convenient. Then set TM core as engine.
    • Similar to the Disorder computation, define three outer shells:
      • Turbomole core, Shelltype dynamic, Cutoff Radius: 15.0 A
      • DFTB+ 1, Shelltype dynamic, Cutoff Radius: 25.0 A
      • DFTB+ 1, Shelltype static, Cutoff Radius: 60.0 A

Output

Distance dependent distribution of electronic couplings are written into files named Js_homo_mol_paris_id0_id1.dat, Js_lumo_mol_paris_id0_id1.dat, Js_dexter_mol_paris_id0_id1.dat in the Analysis/files_for_kmc subdirectory of your QP run.

Command line usage

A settings template for command line usage is available here. To execute EA computation, rename this file to settings_ng.yml and execute QuantumPatch as usal from your command line.

Troubleshooting

Dimer computations of most pairs crash (see error files in runtime folder): This may occur for dimers where a charge transfer is possible, e.g. in doped injection layers. Here we recommend to use m06-2x for the core engine instead of BP.

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