Vibrational spectra of an RDX film over an aluminum substrate from molecular dynamics simulations and density functional theory.
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abstract
We report calculated vibrational spectra in the range of 0-3,500 cm(-1) of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) molecules adsorbed on a model aluminum surface. A molecular film was modeled using two approaches: (1) density functional theory (DFT) was used to optimize a single RDX molecule interacting with its periodic images, and (2) a group of nine molecules extracted from the crystal structure was deposited on the surface and interacted with its periodic images via molecular dynamics (MD) simulations. In both cases, the molecule was initialized in the AAA conformer geometry having the three nitro groups in axial positions, and kept that conformation in the DFT examination, but some molecules were found to change to the AAE conformer (two nitro groups in axial and one in equatorial position) in the MD analysis. The vibrational spectra obtained from both methods are similar to each other, except in the regions where collective RDX intermolecular interactions (captured by MD simulations) are important, and compare fairly well with experimental findings.
