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

Abstract

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 der Waals 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. The static dielectric constant and refractive indices along the three inequivalent crystallographic directions indicate that this material has a considerable optical anisotropy.

Dispersion Corrected Structural Properties and Quasiparticle Band Gaps of Several Organic Energetic Solids

“…There have been promising attempts made to fix this shortcoming, and considerable benchmarking studies are available with advanced methods for noble gas solids, layered, sparse and molecular crystals. [22][23][24][25][26][27][28][29][30][31][32] In the case of energetic materials, Sorescu et al 33 35 From our previous studies on nitromethane and FOX-7 solids, 36,37 we also found good agreement using Grimme and TS methods. However, it is observed that although the mentioned dispersion corrected methods overcomes most of the difficulty in reproducing ground state volumes, the relative errors still show a mean absolute deviation of about 3 %.…”

“…43,44 But the well known disagreement of the computed band gap using standard DFT functionals leads to an inaccurate estimation of the properties related to the band gap either in molecular or solid systems. However from our previous studies on some energetic materials (solid nitromethane, FOX-7, cynauric triazide) 36,37,45 and another theoretical study on TATB by Fedorov et al, 46 it is known that the GW approximation [47][48][49][50][51][52] can overcome this problem.…”

Structure and electronic properties of MNO3 (M: Li, Na, K, NH4) under pressure: DFT-D study

“…Since MNO 3 nitrates contain molecular complexes (nitrate anions, NH 4 cations), it is important to take into consideration the weak intermolecular Van der Waals interactions. DFT can predict the properties of the energetic materials that are in close agreement with experiments provided the exchange-correlation functionals are corrected to describe the weak intermolecular interactions [7,[42][43][44][45][46][47][48]. Thus, in comparison with to the LDA and GGA [49] results , G. Vaitheeswaran et al [7] found that the crystal structure of alkali-metal nitrates is well described by the dispersion-corrected functional DFT-D [50].…”

Влияние давления на структуру и электронные свойства LiClO-=SUB=-4-=/SUB=-, NaClO-=SUB=-4-=/SUB=-, KClO-=SUB=-4-=/SUB=-, NH-=SUB=-4-=/SUB=-ClO-=SUB=-4-=/SUB=-

“…Следовательно, знание структурных Поскольку перхлораты содержат молекулярные ком-плексы (перхлорат-анионы, NH 4 -катионы), важным яв-ляется учет слабого межмолекулярного взаимодействия Ван-Дер-Ваальса. Для этого обменно-корреляционный функционал должен быть скорректирован для описа-ния слабых межмолекулярных взаимодействий [28][29][30][31][32][33][34][35]. Так, в [28][29][30] установлено, что кристаллическая струк-тура хлората калия и нитратов щелочных металлов описывается таким скорректированным функционалом DFT-D [36] значительно лучше по сравнению с LDA и GGA [37].…”