First-principle Molecular Dynamics Study Of Nitromethane Under Shock Compression

Energetic materials are compounds or mixtures that contain explosive groups or oxidants and combustibles,and can independently carry out chemical reactions and output energy.It has been widely used in military and civilian fields.With the progress of science and technology,the performance requirements of energetic materials are getting higher and higher.Therefore,the research of energetic materials has always been a hot issue in the scientific research of various countries.Nitromethane(NM)is the simplest nitrogen-containing energetic material with low cost.As a result,the study of its properties and thermal decomposition mechanism is conducive to understand more complex energetic materials.Although there are a lot of studies on the thermal decomposition of nitromethane,the decomposition mechanism is still controversial.In this paper,the thermal decomposition reaction of nitromethane at different temperatures and compression states is studied through the molecular dynamics simulation based on density functional theory,analyzing the initial reaction mechanism,the population of main products and the evolution process of components of nitromethane.Raman spectra were also simulated.The research results of this paper are mainly described in the following aspects:1.Through analysis on the configurations and the pair correlation functions of nitromethane at different temperatures and compression states,it can be concluded that the reaction of nitromethane is not obvious at 2000 K temperature,although the pressure of the system increases,the reaction is still very slow.The decomposition of nitromethane occurs at 3000 K and 4000 K,and the main products include N2,H2 O,CO2 and macromolecules composed of C and N.2.By analyzing the curve of nitromethane molecule and its main decomposition products changing with time,we can get that the decomposition rate of nitromethane is accelerating with the increase of the compressibility coefficient of the system,which indicates that increasing the pressure of the system can promote the decomposition.The amount of hydrogen peroxide produced in the reaction decreases with the increase of compression coefficient.Nitrogen is a stable decomposition product and will not participate in the subsequent reactions.3.The initial bond breaking type of nitromethane at high temperature(T = 3000 K,4000k)was studied.It was found that when the compression coefficient was 10% and 20%,the C-N bond first scission,instead,when the compression coefficient was 30% and 40%,the C-H bond breaking.It is also found that although the types of first breaking are the same,the following reaction paths are different.4.By analyzing the decomposition products of nitromethane,we found that nitromethane produces many small carbon and nitrogen-containing intermediates in the thermal decomposition reactions under different compression states.As the reaction proceeded,their intermolecular C-N and C-C bonds gradually formed long-chain macromolecules,and the long chains formed were easier to bend to form ring C-N clusters under high pressure.5.The Raman spectra of nitromethane are calculated by using the approximate method of dipole-dipole polarization model.The comparison with the experimental results shows that the Raman spectra obtained by this method are reasonable.