Direct MD Simulations of Terahertz Absorption and 2D Spectroscopy Applied to Explosive Crystals

Area of Science:

• Computational Chemistry
• Materials Science
• Spectroscopy

Background:

• Terahertz (THz) spectroscopy is crucial for analyzing molecular crystals.
• Traditional methods often rely on approximations like linear response and harmonic potentials.
• Accurate simulation of THz spectra is essential for material characterization.

Purpose of the Study:

• To develop and validate a direct molecular dynamics simulation approach for THz spectra.
• To investigate the THz absorption spectra of crystalline cyclotrimethylenetrinitramine (RDX) and triacetone triperoxide (TATP).
• To explore a multidimensional extension of the spectroscopy based on nonlinear response.

Main Methods:

• Direct molecular dynamics simulation incorporating a time-dependent electric field.
• Calculation of absorption spectra from dissipated energy after applying electric field pulses.
• Utilizing the ReaxFF force field for simulating RDX and TATP crystal slabs.
• Simulating a nonlinear response to a single polarized radiation pulse for multidimensional extension.

Main Results:

• The direct simulation method successfully computed the THz spectra of RDX and TATP crystals.
• The approach bypasses the need for linear response and harmonic approximations.
• A multidimensional THz spectrum was simulated, demonstrating the method's extended capabilities.

Conclusions:

• Direct molecular dynamics simulations offer a robust alternative for calculating THz spectra of molecular crystals.
• This method provides a more accurate representation by avoiding approximations.
• The developed technique can be extended to multidimensional spectroscopy for deeper material insights.