Temperature-Dependent Anharmonic Phonons in Quantum Paraelectric KTaO3 by First Principles and Machine-Learned Force Fields

Luigi Ranalli, Carla Verdi, Lorenzo Monacelli, Georg Kresse, Matteo Calandra, Cesare Franchini (Corresponding author)

Publications: Contribution to journalArticlePeer Reviewed

Abstract

Understanding collective phenomena in quantum materials from first principles is a promising route toward engineering materials properties and designing new functionalities. This work examines the quantum paraelectric state, an elusive state of matter characterized by the smooth saturation of the ferroelectric instability at low temperature due to quantum fluctuations associated with anharmonic phonon effects. The temperature-dependent evolution of the soft ferroelectric phonon mode in the quantum paraelectric KTaO3 in the range 0–300 K is modeled by combining density functional theory (DFT) calculations with the stochastic self-consistent harmonic approximation assisted by an on-the-fly machine-learned force field. The calculated data show that including anharmonic terms is essential to stabilize the spurious imaginary ferroelectric phonon predicted by DFT in the harmonic approximation, in agreement with experiments. Augmenting the DFT workflow with machine-learned force fields allows for efficient stochastic sampling of the configuration space using large supercells in a wide temperature range, inaccessible to conventional ab initio protocols. This work proposes a robust computational workflow capable of accounting for collective behaviors involving different degrees of freedom and occurring at large time/length scales, paving the way for precise modeling and control of quantum effects in materials.
Original languageEnglish
Article number2200131
Number of pages7
JournalAdvanced Quantum Technologies
Volume6
Issue number4
Early online date22 Feb 2023
DOIs
Publication statusPublished - Apr 2023

Austrian Fields of Science 2012

  • 103018 Materials physics
  • 102019 Machine learning

Keywords

  • density function theory
  • incipient ferroelectric
  • machine learning
  • phonons
  • quantum materials
  • quantum paraelectric

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