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Updated: Jun 16, 2026

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing
Published on: March 22, 2019
Communications: On artificial frequency shifts in infrared spectra obtained from centroid molecular dynamics: Quantum
Sergei D Ivanov1, Alexander Witt, Motoyuki Shiga
1Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, Bochum 44780, Germany.
Abstract:
Centroid molecular dynamics (CMD) is a popular method to extract approximate quantum dynamics from path integral simulations. Very recently we have shown that CMD gas phase infrared spectra exhibit significant artificial redshifts of stretching peaks, due to the so-called "curvature problem" imprinted by the effective centroid potential. Here we provide evidence that for condensed phases, and in particular for liquid water, CMD produces pronounced artificial redshifts for high-frequency vibrations such as the OH stretching band. This peculiar behavior intrinsic to the CMD method explains part of the unexpectedly large quantum redshifts of the stretching band of liquid water compared to classical frequencies, which is improved after applying a simple and rough "harmonic curvature correction."
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