Morphology Generation

Thin films required for full ab-initio device simulation

In this usecase, atomistic morphologies of thin films are used to compute input for rates of microscopic processes in OLED devices using QuantumPatch. Some quantities such as energy levels (for energy disorder and absolute EA and IP values) need to be computed for multiple molecules in the bulk (i.e. surrounded by molecules of the same species, as is the case in the OLED except at interfaces), other quantities such as excitonic parameters and reorganization energy for a single molecule of each species, and pair parameters (electronic couplings) require multiple pairs of each combination of neighboring molecules present in the OLED. Note that energy levels (both disorder and absolute EA IP levels) change when a pristine material is doped with another compound, e.g. in doped injection layers or in EMLs. We therefore use Deposit to generate the following morphologies:

  • A separate morphology for each layer for the computation of energy levels:
    • MeoTPD doped with F4TCNQ
    • alpha-NPD (pristine)
    • alpha-NPD:Irpiq
    • BPhen
  • A reduced morphology of the full OLED stack containing approx. 400 molecules per layer to compute electronic couplings as well as excitonic properties and reorganization energies. Remark: Excitonics and reorganization energies could as well be computed on the layer morphology. This however would result in four output files for each lambda and excitonics instead of only one each.
Workflow to generate pristine layers of BPhen and alpha-NPD Workflow for Deposition of a mixed film MeoTPD:F4TCNQ including the subsequent parametrization of both compounds (no dihedral-parametrization required for F4TCNQ). Workflow for Deposition of a mixed film of the EML. Irpiq (rigid) is parametrized in the Parametrizer module, input for alpha-NPD is taken from the DihedralParametrizer module in the respective pristine workflow. Subsequent deposition of MeoTPD, alpha-NPD:Irpiq and BPhen with input taken from Parametrizer-Dihedralparametrizer of the other workflows. The pristine alpha-NPD layer is not required in the stack.

Setup of morphology workflows

Morphologies are generated using the standard sub-workflow of Parametrizer, Dihedralparametrizer and Deposit module. An introduction to the general usage of this workflow can be found in the corresponding webinars here and here.

As input we are using mol2 files for each material. You can either create them using any chemical drawing tool, or download these files here

The pre-configured workflows for morphology generation can be downloaded here. This file contains the following files:

  • P_DHP_Deposit_X, X=ANPD, BPhen, for the generation of pristine layers
  • P_P_DHP_Deposit_MeoTPD, for the generation of the MeoTPD:F4TCNQ morphology
  • P_Deposit_Mixed, for the generation of the EML morphology (alpha-NPD with Ir(piq)3)
  • Deposit_Stack, for the generation of the reduced stack morphology

Unzip this container in your local SimStack workflow directory (Configuration -> Paths -> Workflow Workspace) and restart SimStack to access the workflows. Remember to adapt paths to input files where needed. In the following you can find detailed description of the settings, if you wish to modify the workflows or re-create them from scratch.

Parametrization

  • Parametrizer:
    • Input: Mol2 files available here
    • Optimize molecule: True
    • Engine: Turbomole with B3LYP, def2-SVP
    • DFTB pre-optimization enabled except for Irpiq
    • Resources: Up to 32 cores/64GB RAM recommended
  • DihedralParametrizer:
    • Input: Load molecule.pdf and molecule.spf from preceeding Parametrizer module
    • Leave rest as is
    • Resources: Up to 32 cores/64GB RAM recommended

We recommend to save and rename all molecule.pdb and dihedral_forcefield.spf files to your harddrive for later usage.

Deposit

For all depositions, apply the following settings:

  • Simulation Parameters:
    • Simulation Box (all values in Angstrom): Lx=Ly=40.0, Lz=120.0, PBC enabled with cutoff=20.0
    • Initial T: 4000K, Final T: 300K, SA Acceptance T: 5K
    • Number of Steps: 130000 (130 thousand), Number of SA cycles: 32
    • Dihedral Moves: enabled
  • Postprocessing: Extend Morphology enabled, Cutoff first layer by 7Angstrom (standard value)
QP DFT Run

For the individual pristine layer morphologies in the molecules tab, load the molecule.pdb and dihedral_force_field.spf from the DihedralParametrizer module. This way, the molecular information is passed from Parametrizer (starting with anpd.mol2 or bphen.mol2) is passed onto Deposit. Go to the simulation parameters tab, apply all settings above and set "Number of Molecules" to 1000.

For the Deposition of the mixed films (both MeoTPD:F4TCNQ and ANPD:Ir(piq)3), go to the Molecules tab in Deposit and add a second molecule using the "+" button.

  • For the doped injection layer morphology, chose output of the dihedralparametrizer module (molecule.pdb, dihedral_forcefield.spf) as input, and for the second molecule use the output of the parametrization module (molecule.pdb, molecule.spf) where F4TCNQ.mol2 was used as input. Make sure that the dihedral parametrization is based on the input from the parametrizer module starting with MeoTPD. Set concentrations to 0.9 and 0.1 for host and dopant respectively. For the EML, as first molecule, load anpd.pdb and anpd_dihedral_forcefield.spf from your hard drive and set the concentration to 0.85.
  • For the second molecule, load molecule.pdb and molecule.spf from the Parametrizer WaNo (Irpiq) using the blue button on the right of the respective fields. Set the concentration of the second molecule to 0.15. Note that the figure to the right illustrating the setup of a mixed film depicts incorrect concentrations. Finally to the simulation parameters tab, apply all settings above and set "Number of Molecules" to 1200 (a bit more than the pristine films for statistics).

For the stack deposition you have three subsequent Deposit WaNos. In the first Deposit WaNo, go to the Molecules tab and load meotpd.pdb and meotpd_dihedral_forcefield.spf from your harddrive. In the second WaNo, in the Molecules tab, specify the input as for the mixed film above. Additionaly, also in the Molecules tab, check the "restart from existing morphology" checkbox and, using the blue button to the right of the "Restartfile filed", load restartfile.zip from the first Deposit WaNo. Proceed similar in the third WaNo and load the restartfile from the second WaNo, to deposit BPhen on top of MeoTPD and the mixed EML. Finally, go to the "Simulation Parameters" tab in each WaNo and set the number of molecules to 500 for MeoTPD (first layer will be cut) and 400 for each the mixed EML and the BPhen layer. Remember to enable PBC extension and first-layer-cutoff at least in the last Deposit WaNo of this workflow (Postprocessing tab).

Resources: We recommend to allocate 32 cores on a single node with 64GB RAM for parallel execution of the 32 SA cycles and optimal performance.

Output

From each Deposit run, download the structurePBC.cml and save them locally for further usage in QuantumPatch. Note that it is important to use the files ending on "PBC.cml" instead of files namend structure.cml, as these "*PBC.cml" contain periodic images of all molecules in x-y-direction to create sufficient electrostatic environment for QuantumPatch. In the subsequent tutorial on electronic structure analysis for full stack simulations, we refer to the output files as meotpd_doped_structurePBC.cml, bphen_structurePBC.cml, anpd_structurePBC.cml, anpd_irpiq_structurePBC.cml, stack_structurePBC.cml respectively. If you wish to skip the morphology generation and continue with QuantumPatch, you can find the morphologies for download here.

Next step: electronic structure analysis

Click here to run electronic structure analysis in QuantumPatch on morphologies

Troubleshooting

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