First-principle Studies On Phonon Spectra And Thermodynamic Properties Of CL-20-based Cocrystals And Co-formers

Although the explosion of energetic materials has been recognized for thousands of years,the initial reaction mechanism of detonation is very limited from a microscopic perspective.The conversion of externally stimulated mechanical energy into a specific path of molecular excitation is a meaningful subject,both from the perspective of energy transition and lattice vibration.Phonon spectroscopy is the basis of lattice vibration.The thermodynamic properties and energy flow directions of CL-20 crystals and co-crystals can be studied from the lattice dynamic,and the microscopic physical nature has been revealed for thermal decomposition mechanism,denotation performance and sensitivity.This thesis is based on the structure-activity relationship between the phonon spectrum and the physical and chemical properties of the materials.CL-20/MTNP and CL-20/1,4-DNI cocrystals are used as research objects.By analyzing the theoretical phonon spectra of cocrystals and co-formers,the micro-physical mechanism of cocrystal explosives is explored in depth,and important information is provided for the energy transfer process before chemical decomposition.Based on this,this paper used DFT-PBE method and TS dispersion correction to calculate the phonon spectrum of different crystal forms??-,?-,?-?CL-20,CL-20/MTNP cocrystal,and CL-20/1,4-DNI cocrystal.The main conclusions are as follows:1.Investigation on the phonon spectra and thermodynamic properties of various crystal forms of CL-20:The phonon spectrum,raman active vibration frequency,constant volume heat capacity,entropy and enthalpy of co-formers??-,?-,?-CL-20?were calculated,respectively.It could be provide theoretical data for related studies of different crystal forms CL-20.The way in which the phonon mode storage and transfers energy was determined,and the direction of thermal energy flow,trigger bond were proposed through analyzing the phonon density of states.The calculation results for?-,?-,and?-CL-20 crystals indicate that theoretically simulated phonon spectra can be consistent with literature values in the low frequency region,but slightly deviated in the high frequency region.In the temperature range of 0⁶00K,the thermodynamic properties of different crystal forms CL-20 are only slightly different.The initiation bonds of different crystal forms CL-20 are N–NO₂,and during the initial initiation process,energy transfer may undergo a multi-phonon pumping process.2.Investigation on the phonon spectra and thermodynamic properties of CL-20/MTNP cocrystal and MTNP crystal:The phonon spectrum and relationship between thermodynamic parameters and temperature were calculated,and the phonon mode storage and energy transfer methods were obtained.By comparing the phonon density of states of the cocrystal and co-formers?CL-20 and MTNP?,It can investigate the microscopic physical mechanism of initial thermal decomposition mechanism,detonation performance and sensitivity.The results show that in the CL-20/MTNP cocrystal,CL-20 molecules absorb and transfer more energy and have thermal instability.Therefore,the initial thermal decomposition of CL-20/MTNP cocrystal may begin with the N–NO₂ bonds of the CL-20 molecules,and CL-20 molecules play a leading role in the detonation performance of the cocrystal.Based on the"doorway"mode number and characteristic vibration frequency??_d,the impact sensitivity order of the cocrystal and co-formers is predicted to be?-CL-20>CL-20/MTNP>MTNP,which is consistent with the experimental results.3.Investigation on the phonon spectra and thermodynamic properties of CL-20/1,4-DNI cocrystal and 1,4-DNI crystal:The density functional theory with dispersion correction was used to calculate the phonon spectra and thermodynamic parameters of CL-20/1,4-DNI cocrystal and co-formers.By analyzing the phonon density of states,it is helpful to study its thermal decomposition mechanism,detonation performance and sensitivity.The results show that the initial bonds of CL-20/1,4-DNI cocrystal is predicted to be N-NO₂ bonds on CL-20molecules;the initial thermal decomposition of 1,4-DNI crystal may be related to the imidazole ring.And after the formation of the cocrystal,the thermal stability of both CL-20molecules and 1,4-DNI molecules is improved,which shows that the thermal stability of the cocrystal is better than those of co-formers.The"doorway"mode number and characteristic vibration frequency??_d of the cocrystal and co-formers are linearly related to the impact sensitivity,which can be used as two empirical methods to predict the impact sensitivity order.