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aMotivated by the recent realization of two-dimensional (2D) nanomaterials as gas sensors, we have investigated the adsorption of gas molecules (SO 2 , NO 2 , HCN, NH 3 , H 2 S, CO, NO, O 2 , H 2 , CO 2 , and H 2 O) on the graphitic GaN sheet (PL-GaN) using density functional theory calculations. It is found that among these gases, only SO 2 and NH 3 gas molecules are chemisorbed on the PL-GaN sheet with apparent charge transfer and reasonable adsorption energies. The electronic properties (especially the electric conductivity) of the PL-GaN sheet showed dramatic changes after the adsorption of NH 3 and SO 2 molecules. However, the strong adsorption of SO 2 on the PL-GaN sheet makes desorption difficult, which precludes its application to SO 2 sensors. Therefore, the PL-GaN sheet should be a highly sensitive and selective NH 3 sensor with short recovery time. Furthermore, the adsorption of NO (or NO 2 ) molecules introduces spin polarization in the PL-GaN sheet with a magnetic moment of about 1 m B , indicating that magnetic properties of the PL-GaN sheet are changed obviously. Based on the change of magnetic properties of the PL-GaN sheet before and after molecule adsorption, the PL-GaN sheet could be used as a highly selective magnetic gas sensor for NO and NO 2 detection.

A first-principles plane-wave method with an ultrasoft pseudopotential scheme in the framework of the generalized gradient approximation (GGA) was used to calculate the lattice parameters, bulk modulus and its pressure derivative, energy band structures, density of states, phonon density of states, thermodynamic properties, and absorption spectra of solid beta-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (beta-HMX). The current study is focused on the thermodynamics and electronic properties that were not reported previously. The bulk modulus and its pressure derivative are also consistent with experimental data and other theoretical results. From the results for the band gaps and density of states, it was found that beta-HMX has the tendency to become a semiconductor with increasing pressure. As the temperature increases, the heat capacity, enthalpy, product of temperature and entropy, and Debye temperature all increase, whereas the free energy decreases. The optical absorption coefficients shift to higher frequencies/energies with increasing pressure. The present study leads to a better understanding of how energetic materials respond to compression.