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Local spin and open quantum systems: clarifying misconceptions, unifying approaches.

A Martín Pendás1, E Francisco

  • 1Departamento de Química Física y Analítica, Universidad de Oviedo, Oviedo, Spain. ampendas@uniovi.es.

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Summary
This summary is machine-generated.

Open quantum systems (OQSs) theory explains local spins in molecules by partitioning spin operators. This approach resolves inconsistencies in existing definitions and clarifies spin behavior in various electron correlation scenarios.

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Area of Science:

  • Quantum Chemistry
  • Theoretical Chemistry
  • Molecular Physics

Background:

  • The concept of local spins in molecules, particularly in closed-shell systems, has led to various definitions and inconsistencies.
  • Existing methods struggle to consistently explain non-zero local spin values in closed-shell molecules.

Purpose of the Study:

  • To apply the theory of open quantum systems (OQSs) to consistently define and analyze local spins in molecular systems.
  • To provide a unified framework for understanding localized and itinerant spins and their arrangements.
  • To investigate the role of electron correlation in the emergence of local spins.

Main Methods:

  • Partitioning of the squared spin operator into fragment (local) and interfragment (coupling) contributions using OQS theory.
  • Description of atomic or fragment subsystems using quantum mechanical mixed density operators with electron number sectors.
  • Analysis of the Hubbard Hamiltonian in small chains to study electron correlation effects.

Main Results:

  • OQS fragment spin operators are consistent with established theories of local operators.
  • The OQS approach uniquely rationalizes non-zero local spins in closed-shell molecules, highlighting inconsistencies in prior definitions.
  • Models for localized and itinerant spins are developed and used to classify spin arrangements.
  • Electron correlation is shown to play a crucial role, with local spins arising from the interplay of localized and delocalized electrons.

Conclusions:

  • The OQS framework offers a robust and consistent method for defining and analyzing local spins in molecular systems.
  • This perspective simplifies the construction of models for diverse spin behaviors and clarifies chemical patterns.
  • The study provides a unified understanding of local spin phenomena, resolving long-standing theoretical challenges.