LightForge GUI

Introduction to the LightForge GUI

As a multipurpose KMC program, LightForge offers a variety of modes of operation, options and ways to provide input for device simulation and the GUI that may be confusing at first sight. However we did our best to make the reducing complexity where possible, while exposing required functionality for both research new to LightForge and expert users. To this end you will find various check boxes throughout the LightForge GUI that allows the user to modify standard values, or supply additional settings. Whenever in doubt, we recommend to stick to the standard values.

The LightForge GUI consists of 7 tabs, through which we will guide you one by one below:

  • general: Defines the mode how the "digital twin" of your device is set up, and determines which options are available in the other tabs.
  • IO: If the LightForge run is based on microscopic parameters computed with QuantumPatch, all QuantumPatch output files can be supplied here as input.
  • materials: In this tab, material specific parameters can be supplied for all materials, either by hand or by assigning a specific QuantumPatch file to each material. Also, the method to compute excitonic rates is set here.
  • device: Define layer structure and electrode settings.
  • topology: In this tab you can define the settings for the topology, i.e. pair parameters such as electronic couplings for holes and electrons
  • physics: Here you can chose between different physical models (e.g. rate models) implemented in LightForge.
  • operation: Set up your virtual experiment, e.g. define applied electric fields or temperature.

"general" tab

  • device layout:
    • stack: This option should be used in most simulations, especially multilayer OLED stacks. Here the layer morphology are automatically stacked on top of each other with correct molecular distances between layers and between outermost layers and the electrodes.
    • manual: Use this option to manually place all layers by defining their center and dimension. Multiple electrodes can be applied e.g. for transistors. For advanced users only.
  • setPBC: periodic boundary condition (PBC) settings
    • automatic: PBC in y- and z-direction are applied and the field is applied in x-direction.
    • manual: PBC in x-, y- and z-direction are set by the user.
  • connect electrodes: If checked, electrodes are used to simulate injection of charge carriers into the device. For specific use cases, e.g. computation of field-dependent charge carrier mobility in bulk systems, electrodes are not required and the usage of periodic boundary conditions in all three dimensions can be applied.
  • particle types: Only checked particle types are considered in the KMC simulation. For a full device, electrons, holes and excitons are required. For charge carrier mobility simulations, for example, only holes or electrons are needed. Checking or unchecking particle types en-/disables different settings e.g. in the materials tab.

"IO" tab

  • use QP output: Uncheck this box if you want to supply all parameters manually. Keep this option checked if some or all parameters should be taken from QuantumPatch output.
  • QP output file box: Microscopic parameters can be read in from multiple QuantumPatch output files. Use the plus-/minus button to add or remove files.
    • name: Give each file a unique identifier that is later needed to assign QP files to materials. These identifiers will appear in drop-down menues in the materials, device and topology tab.
    • QP_output.zip: Load a file from your hard drive or chose a file from a preceding QP run in a workflow.

"materials" tab

Note: Your materials tab looks different than the one displayed in the picture above. Certain options are disabled depending on parameters suppied in other tabs, e.g. particles in the "general" tab, and then not displayed for clarity.

  • excitonics: You have different options to compute exciton dynamics in LightForge:
    • use QP ab-initio input: Where possible, microscopic results from QuantumPatch are used to compute material specific excitonic rates. For everything that is not computed by QuantumPatch, presents are used (see also "show exciton_presets" below). Only for this option, the "QP_output_excitonics" dropdown is available in the "materials" box.
    • use presets: All excitonic parameters are computed using standard presets. A detailed documentation of the presets will follow shortly.
    • use heuristic parameters: heuristic models are used to compute rates for exciton dynamics. In this case, the user can supply singlet and triplet Foerster radii for all pairs of molecule types in the "topology" tab.
    • no excitons: Use this option if no excitons are used in the simulation, e.g. for charge carrier mobility simulations.
  • materials box: Each material used in the KMC simulation is defined here. If your system includes 5 compounds, click the plus-buttom 4 times to add four materials.
    • name: Define a unique identifyer for each material. This identifyer will appear in various drop down menues in other tabs.
    • input_mode_transport: For each material, chose which of the transport parameters (disorder, EA&IP, reorganization energy lambda) should be taken from QP output or supplied manually. In the options of the drop down menue, parameters listed after "QP" are taken from QP, parameters listed after "PAR" are set by the user below.
    • molecule parameters box: Energetic parameters (sigma, lambda, EA&IP) change from drop down to tables, if the user wants to supply them manually (see input_mode_transport above).
      • molecule_pdb: As any QP output file can contain information for multiple materials, we use the single-molecule pdb file used in Deposit to connect information stored in a QP output file to a certain material. This file needs to be provided here, either from the hard drive or from a previous module in the workflow (Parametrizer, DihedralParametrizer or Deposit).
      • QP_output_X: Dropdown menue to chose the QP output file to extract energy quantity X (X=sigma, lambda, EAIP) for this material, from the list of all QP output files provided in the IO section. Depending on the input_transport_mode above, the respecitve dropdown menues disappear and values can be supplied in the energies table.
      • energies: Manually insert parameters not extracted from QP output.
      • exciton preset: Chose fluorescent or phosphorescent exction presets for this material.
  • show exciton_presets: Show and modify exciton presets. In case of doubt, do not change the presets.

"device" tab

  • morphology width [nm]: Defines the width of the simulated stack. As of now, all layers defined below have the same width in the KMC simulation.

  • layers: Add or remove layers to your stack structure using plus- or minus-button.

    • thickness: defines the thickness of a layer in nm
    • morphology_input_mode:
      • select QP output: A morphology generated with Deposit is taken from a QP output. Using this option, the user can then chose the respective QP output, as defined in the IO-tab, from the otherwise hidden "morphology_QP_output" drop-down menue.
      • cubic: Use a simple cubic lattice with lattice constant of 1nm as morphology. This is a good approach to include additional layers in KMC, using a parametric approach without having to run the full workflow (Parametrizer+Deposit+QP).
      • Custom files: morphology: Read in center of geometry for this layer from a file, where each lines contains x,y and z coordinate and an integer label in the 4th column.
      • Custom files: morphology, eaip: Along with the center of geometry you can supply an additional file containing site-specific EA and IP energy levels. This is a useful option for non-standard device setups such as gradual doping.
    • molecule_species: adapt the number of materials ("molecule species") in the layer to simulate pristine or mixed layers, chose your molecules as defined in the materials section and adapt the concentrations.

  • electrodes: Define work functions and coupling models for electrodes. This option is hidden, if "connect_electrodes" in the general tab is disabled. There are three models available to compute coupling between electrodes and the organic layers:

    • QP_output: Couplings between the nearest organic layer and electrode are computed based on averaged distance dependent organic-organic couplings. This coupling can be scaled in electrode_J_stack_scaling in the advanced settings in the physics tab.
    • QM_fit: This works similar to the QP_output option, but any distance-coupling distribution can be provided in the electrode_coupling_file field (appears if this option is used). The format of the file provided should be distance in Angstrom in the first column and electronic couplings in eV in the second column.
    • parametrized: Couplings between nearest organic material and electrode are computed based on Miller-Abrahams rates using the electrode_coupling value as square-root of the prefactor and the value in the electrode_wf_decay_length field as inverse decay length (prefactor in the exponent of the Miller-Abrahams rates).

  • morphology expansion scheme: Morphologies can be expanded to run KMC simulations on layers that are larger than the morphologies used to compute microscopic input. There are three expansion schemes available:

    • lfx: Iterative boltzmann inversion to generate a site distribution with correct Radial Distribution Function. We recommend to use this option.
    • edcm: Extended dominance competition model. While this is slightly more robust than lfx, it does not work with highly isotropic densely packed molecules.
    • no expansion: If you wish to use the exact morphology provided in a morphology file/QP file (e.g. for Bulk Heterojunctions), use this option. Please note that layer dimensions in the device tab have to match the layer dimensions in the morphology file provided.

"topology" tab

  • max neighbors: Number of nearest neighbors to take into account for charge carrier and exciton dynamics.
  • transfer integral source: The options in this drop-down menue determine how transfer integrals (Js) between pairs of molecules are computed. There are three options available:
    • QP_output: For each pair, chose a QP output file identifyer (defined in the IO tab) to extract transfer integrals from QP runs. Make sure that Js were actually calculated in the respective QP run (see the QuantumPatch GUI for reference)
    • QM_expansion: If enabled, three files can be provided for each pair of molecules below for hole, electron and Dexter transfer integrals. These files need to be formatted with the distances in Angstrom in the first column, and the coupling in eV in the second column.
    • Miller-Abrahams: This option computes transfer integrals using Miller-Abrahams formalism. If this option is used, the user needs to provide wave function decay lengths and a maximal values for transfer integrals for each pair of molecules in the pair parameters section below.
  • pair parameters: Use the plus-buttom to add as many pairs of materials as required.
    • molecule 1 and molecule 2: Chose the identifiers as defined in the materials tab.
    • transfer_integral_parameters: Provide either input files or parameters, depending on the mode set in "transfer integral source" above.

"physics" tab

  • rates: Charge transfer rates can be computed using either Marcus or Miller-Abrahams formalism
  • epsilon_material: Dielectric constant of the OLED. As of now, only a global parameter can be applied and we recommend to use 4.0.
  • superexchange: Enable second-order charge transfer via virtually occupied intermediate states. This option increases computation time, but also provides more accurate results.
  • show advanced: Enables the user to additionally set the following parameters:
    • distance_epsilon: As there is no matter but only vacuum between neighboring molecules in a thin film, a distance-dependent epsilon can be used.
    • screening_length: Required for distance dependent dielectric constant. This value is a measure for how quickly the dielectric constant goes from 1.0 to the bulk value provided above.
    • doping: Enables integer charge transfer between uncharged molecules. Currently does not work in combination with exciton dynamics simulations, however the exciton box needs to be checked in the general tab due to technical reasons.
    • doping_regeneration_steps: Refresh rate for bleached CT sites. Further documentation in progress. Default value sufficient for all values.
    • electrode_stack_distance: Change this value to account for injection effects at the electrode, e.g. tunneling through thin insulating layers.
    • electrode_J_scale: This enables the user to shift the coupling between organic material and electrode by X times the distance-dependent widht of the coupling distribution, where X is given in this field.

"operations" tab

  • restart: Restart the KMC simulation from a previous KMC run. If checked, the restartfile (output of KMC) needs to be provided.
  • simulations: To get converged results with sufficient statistics, each "virtual experiment" should be performed multiple times. We recommend to start with a low value to check if all inputs are provided accurately, but perform 10 or more simulations for quantitative analysis.
  • measurement: Only DC available, currently.
  • temperature: Device temperature in K.
  • field strength: Separated by spaces, supply values for the electric field in the KMC simulation, in V/nm.
  • initial holes and electrons: A fixed number of charge carriers can be assigned randomly on sites in the sample. This becomes especially relevant, if no electrodes are connected (e.g. during full PBC computations of bulk properties such as mobility), i.e. no charge carriers can be injected. The availability of this option depends on the particle_types settings in the general tab.
  • computational: Convergence criteria for LightForge runs. The simulation is either terminated, if the relative change of the I-V between subsequent simulation steps drops below the value supplied in the IV fluctuation field, or if the number of steps reaches max_iterations.
  • activate bond damping: Damps rates for back- and forth processes to increase simulation efficiency. This option should be activated, if test simulations show that most simulation steps are used on these rattle type processes, e.g. at interfaces or near electrodes. Use with care and for now only modify the following three values:
    • max bond noise: If activated bond damping affects physical results (such as current density), increase max bond noise.
    • max damp factor: If bond damping does not show any effect, increase this value, but do not exceed 0.35.
    • healing: increase this value along with an increase in max damp factor.

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