Thesis (M.Sc.)--Chulalongkorn University, 2013

The carbon nitride methanediide, C₂N₂(CH₂), has been newly discovered in 2011. This compound contains the C-N single bond, the same as in a super hard material carbon nitride, C₃N₄. The band gap of C2N2(CH2) is around 6 eV. Thus, it is classi ed as a wide-band gap semiconductor which has many applications. However, the knowledge of C₂N₂(CH₂) is limited; especially, its properties under high pressure. In this thesis, we investigate the mechanical and electronic properties of C₂N₂(CH₂) under high pressure, in the range of 0-50 GPa, using density functional theory (DFT). The non-local exchange-correlation functional calculation, sX-LDA, which is the most accurate tool to simulate wide-band gap materials, is performed. Our result shows that the C₂N₂(CH₂) band gap is 6.07 eV, using the sX-LDA, and it decreases as pressure increases. Moreover, we nd the relation between the N1-C1-N2 angle change and the band gap. The bulk modulus of C₂N₂(CH₂) is 254 GPa from our calculation which is in good agreement with the experimental data. The bond contractions of C-N and C-C single bonds are explored. We nd that the C-N bond contraction in C₂N₂(CH₂) is the same as those in C3N4. However, the C-C bond contraction in C₂N₂(CH₂)is larger than those in diamond. This leads to the lower bulk modulus compared with that of diamond. The Cmc21 structure stability of C₂N₂(CH₂) is examined and found that it has dynamical and mechanical stabilities. The Raman spectrum of C₂N₂(CH₂) is predicted for the rst time in this work, and compared with references from other systems.