Lumabi: Luminescence Lineshape of Point Defects

Lumabi: Luminescence Lineshape of Point Defects#

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These chapters introduce Lumabi, a collection of Python modules integrated in the AbiPy framework and designed to compute the luminescence lineshape of point defects in solids with Abinit.

Overview#

Lumabi is structured around four main Python modules, each automating a key stage of the computational workflow for phonon-resolved luminescence spectra of defects. These modules can be used separately or together, with the output of one module serving as input for another.

1. LumiWork Module#

The LumiWork module, an AbiPy Workflow that automates ABINIT DFT tasks with SCF constrained occupations.

The LumiWork module automates ABINIT DFT tasks with \(\Delta\)SCF constrained occupations. It manages two structural relaxations (ground state and excited state), as well as optional static SCF and NSCF band structure calculations. The main results are stored in netcdf files, ready for post-processing.

2. \(\Delta\)SCF Post-Processing Module#

The SCF module, designed to post-process SCF constrained-occupation calculations using a one-dimensional configuration-coordinate model.

This module processes the netcdf output files produced by LumiWork and analyzes them with a one-dimensional configuration coordinate model (1D-CCM). It computes transition energies, Huang-Rhys factors, effective phonon frequencies and lineshapes within the 1D-CCM, and helps analyze atomic relaxations.

3. Lineshape Calculation Module#

The lineshape module, used to compute temperature-dependent spectra.

Here, we adopt a multi-phonon approach, or multi-dimensional configuration coordinate model (multi-D CCM). The Lineshape module computes the Huang-Rhys spectral function and generates (temperature-dependent) photoluminescence spectra using the generating function approach. It takes as input the zero-phonon line energy, the atomic displacements or forces, and the phonon modes (possibly from the IFCs embedding module), and produces the final phonon-resolved luminescence spectrum.

4. IFCs Embedding Module#

The IFCs embedding module, used to compute defect phonons in large supercells.

The IFCs Embedding module enables the calculation of defect phonons in large supercells by combining the interatomic force constants (IFCs) of the pristine and defect systems. This approach captures the coupling with both long-wavelength and localized phonon modes.

Tutorial structure#

This tutorial is organized as follows:

  1. Theory: Presents the formalism for luminescence lineshape calculations, from Fermi’s golden rule to practical models for solids, and introduces the Huang-Rhys theory and generating function approach. It then discusses some aspects of the computational methodology, including the \(\Delta\)SCF method, the use of forces instead of displacements, and the IFCs embedding approach.

  2. LumiWork Workflow: Guides you through setting up and running the automated workflow for \(\Delta\)SCF calculations with the lumiwork module.

  3. \(\Delta\)SCF Post-Processing (1D): Shows how to analyze the results of a LumiWork workflow within the 1D-CCM (single effective phonon mode model) with the deltaSCF module.

  4. Lineshape (multi-phonon): Explains how to compute the phonon-resolved luminescence spectrum with the lineshape module using the generating function approach.

  5. IFC Embedding: Details the embedding approach of the embedding_ifc module for obtaining phonon modes in large supercells with defects.