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September 10, 2026International Journal of Theoretical PhysicsOpen Access

The Born–Oppenheimer Approximation From the QU Decomposition of Bilinearly Coupled Harmonic Oscillators

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Authors

CACarlos A. ArangoIcesi University

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Overview

Mathematical analysis demonstrates the derivation of the Born-Oppenheimer approximation from Iwasawa factorization in coupled oscillators, highlighting an algebraic basis for adiabatic behavior.

Key Points

  • To establish a rigorous mathematical connection between the Born–Oppenheimer approximation and the matrix decomposition of coordinate transformations in bilinearly coupled harmonic oscillators.
  • Explicitly computed the linear transformation in GL(2, R) mapping physical coordinates to normal-mode coordinates for two bilinearly coupled harmonic oscillators.
  • Applied a unique QU (Iwasawa) factorization to decompose the transformation into an orthogonal mixing component and an upper-triangular hierarchical component.
  • Conducted numerical evaluations comparing exact energies and wavefunctions against the Born–Oppenheimer approximation across various coupling strengths and frequency regimes.
  • The upper-triangular matrix factor directly corresponds to the Born–Oppenheimer approximation by capturing the hierarchical dependence of fast coordinates on slow coordinates.
  • In the adiabatic limit characterized by a small frequency ratio, the orthogonal component becomes negligible, causing the full coordinate transformation to converge onto the Born–Oppenheimer mapping.
  • Numerical tests confirmed agreement between exact solutions and the approximation across multiple coupling regimes.

Cite This Study

Carlos A. Arango (2026) studied this question.

synapsesocial.com/papers/6aa27ad858559d80afc73a72https://doi.org/10.1007/s10773-026-06476-1
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