Ab initio molecular dynamics simulation of vibrational energy redistribution of selective excitation of C–H stretching vibrations for solid nitromethane

Abstract

Vibrational energy redistribution after selective excitation in nitromethane was simulated by ab initio molecular dynamics which could be directly compared with the 3D IR-Raman spectra, and provide more information of the internal mechanism.

Vibrational energy redistribution in crystalline nitromethane simulated by ab initio molecular dynamics

“…And the vibrational modes (M9–M10) at 1000 cm −1 appear at the beginning but their intensities remain weak. The general evolutionary trends are consistent with those in our previous work 26 and are also in qualitative agreement with the experimental results by Dlott's group. 16 …”

“…Complete details of AIMD, normal modes decomposition and drawing of 3D excitation and detected vibrational spectra can be found in our prior work, 26 here only a brief description will be given. All the calculations were conducted in Vienna Ab initio Simulation Package (VASP) with PBE functional, PAW potential and Grimme's D3 correction.…”

“…It's important to note that our calculation here ignores the nuclear quantum effect (NQE) which would not have a significant influence on the coupling mechanism and transfer process according to our simulations at 300 K (400 K) for solid (gaseous) NM. 26,27 …”

“…In one selective excitation, the four-fold degenerate lattice modes corresponding to one molecular vibration were excited simultaneously. Instead of the treatments for selective excitation in the previous work, 26 the positions of all atoms were kept unchanged during the excitation in order to be more consistent with the case of actual optical excitations. According to the Parseval's theorem, 36 the integration of one mode's SED in frequency domain equals the integration of its energy in time domain.…”

“…It showed that AIMD simulation is a powerful tool to reveal the corresponding coupling mechanisms in solid NM. 26 The spectral energy of density (SED) of vibrational modes are obtained by combining the normal modes decomposition and the short-time Fourier transform (STFT), which show that the anharmonic vibrational couplings are related to the symmetries of the normal modes. The AIMD simulation is also appropriate to single molecule.…”