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Dynamical kernels for optical excitations.

Juliette Authier1, Pierre-François Loos1

  • 1Laboratoire de Chimie et Physique Quantiques (UMR 5626), Université de Toulouse, CNRS, UPS, Toulouse, France.

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Summary
This summary is machine-generated.

Dynamical kernels in linear response theory reveal additional excitations, including double excitations, due to their frequency-dependent nature. Analysis also identifies spurious excitations arising from kernel approximations.

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Area of Science:

  • * Computational physics and chemistry.
  • * Quantum mechanics and electronic structure theory.

Background:

  • * Linear response theory is crucial for calculating optical excitations.
  • * Dynamical kernels, frequency-dependent, offer a more accurate approach than static kernels.
  • * Previous studies have highlighted issues with spurious excitations in approximate kernels.

Purpose of the Study:

  • * To evaluate the physical properties and accuracy of three distinct dynamical kernels.
  • * To investigate the capability of dynamical kernels in capturing higher-order excitations.
  • * To analyze the emergence of spurious excitations from approximate dynamical kernels.

Main Methods:

  • * Implementation and analysis of three dynamical kernels: a dressed time-dependent density-functional theory (TDDFT) inspired kernel, a Bethe-Salpeter equation (BSE) kernel, and a second-order BSE kernel.
  • * Utilizing a simple two-level model for calculations.
  • * Examining prototypical examples of valence, charge-transfer, and Rydberg excited states.

Main Results:

  • * Dynamical kernels provide additional excitations, including those corresponding to double excitations, which are often missed by static approaches.
  • * The frequency-dependent nature of these kernels is key to capturing these higher-order phenomena.
  • * Spurious excitations were identified in each kernel, stemming from their approximate formulations.

Conclusions:

  • * Dynamical kernels are valuable for a more complete description of optical excitations, particularly for higher-order states.
  • * Careful consideration of kernel approximations is necessary to avoid unphysical results.
  • * The study provides insights into the strengths and weaknesses of different dynamical kernel approaches in electronic structure calculations.