EFFECT OF VACANCY DEFECTS ON THE TERAHERTZ SPECTRUM OF CRYSTALLINE PENTAERYTHRITOL TETRANITRATE
A Pereverzev and TD Sewell, SHOCK COMPRESSION OF CONDENSED MATTER - 2011, PTS 1 AND 2, 1426 (2012).
Molecular dynamics was used to study the effect of molecular vacancies on the terahertz (THz) infrared (IR) absorption spectrum of crystalline pentaerythritol tetranitrate (PETN). Three-dimensionally periodic simulation supercells containing either 10 percent or 20 percent vacancies were created by randomly removing molecules from the perfect crystal supercell. Following re-equilibration of the defective materials, which remained crystalline on the 170 ps time scale of the simulations, THz spectra were determined from isochoric-isoergic trajectories as the Fourier transform of the ensemble-averaged equilibrium dipole-dipole time autocorrelation function. The calculated spectra exhibit substantial peak broadening and increase in the low- frequency absorption intensity with increasing vacancy concentration. Spectral redshifting with increasing vacancy concentration was also observed, in particular for the higher-frequency member of the pair of peaks comprising the main THz-region IR absorption in crystalline PETN.
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