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A DFT study of structural, dynamical properties and quasiparticle band structure of solid nitromethane

We report a detailed theoretical study of the structural, vibrational, and optical properties of solid nitromethane using first principles density functional calculations. The ground state properties were calculated using a plane wave pseudopotential code with either the local density approximation (LDA), the generalized gradient approximation (GGA), or with a correction to include van derWaals interactions. Our calculated equilibrium lattice parameters and volume using a dispersion correction are found to be in reasonable agreement with the experimental results. Also, our calculations reproduce the experimental trends in the structural properties at high pressure. It was found to be a discontinuity in the bond length, bond angles and also a weaking of hydrogen bond strength in the pressure range from 10 to 12 GPa, picturing the structural transition from phase I to Phase II. Moreover, we predict the elastic constants of solid nitromethane and found that the corresponding bulk modulus is in good agreement with experiments. The calculated elastic constants are showing an order of C11> C22 > C33, indicating that the material is more compressible along the c-axis. We also calculated the zone center vibrational frequencies and discuss the internal and external modes of this material under pressure. From this, we found the softing of lattice modes around 8 to 12 GPa. We have also attempt the quasiparticle band structure of solid nitromethane with the G0W0 approximation and found that nitromethane is an indirect band gap insulator with a value of the band gap of about 7.8 eV with G0W0 approximation. Finally, the optical properties of this material, namely the absorptive and dispersive part of the dielectric function, and the refractive index and absorption spectra are calculated and the contribution of different transition peaks of the absorption spectra are analyzed.