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Anharmonic Phonon Dispersion in Polyethylene.

Xiuyi Qin¹, So Hirata¹

¹Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.

The Journal of Physical Chemistry. B

|November 10, 2020

Summary

This summary is machine-generated.

This study applies the Green's function method to anharmonic crystals, revealing that self-consistent calculations avoid divergences and explain vibrational spectra details in polyethylene.

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Area of Science:

Solid State Physics
Computational Materials Science
Spectroscopy

Background:

Anharmonicity in crystals significantly impacts vibrational properties.
Previous methods struggled with divergences in calculating anharmonic phonon spectra.
Polyethylene's vibrational spectra contain unexplained smaller features.

Purpose of the Study:

To apply the second-order Green's function method to anharmonic polyethylene.
To investigate the role of quartic force constants in phonon behavior.
To resolve divergences and explain spectral features using a self-consistent approach.

Main Methods:

Utilized the second-order Green's function method.
Incorporated up to quartic force constants for polyethylene.
Employed a frequency-dependent Dyson self-energy solved self-consistently.

Main Results:

The self-consistent method successfully avoided spurious divergences.
Identified true resonances in anharmonic phonon dispersion and density of states.
Provided new insights into previously unexplained features of vibrational spectra.

Conclusions:

The self-consistent Green's function method is robust for anharmonic systems.
Detailed understanding of anharmonic phonon behavior in polyethylene was achieved.
This approach offers a pathway to interpret complex vibrational spectra.