TY - JOUR
T1 - First-principles simulation of cyanogen under high pressure
T2 - Formation of paracyanogen and an insulating carbon nitride solid
AU - Khazaei, Mohammad
AU - Tripathi, Madhvendra Nath
AU - Kawazoe, Yoshiyuki
PY - 2011/4/8
Y1 - 2011/4/8
N2 - Using a set of first-principles calculations, we have studied the phase transitions of cyanogen molecules (C2N2) under high pressure. We obtained that at high pressure, cyanogen is transformed to a planar graphitelike structure with metallic property, which is experimentally known as paracyanogen. By increasing pressure, paracyanogen is transformed to an insulator carbon-nitrogen solid with an indirect band gap of 3.2 eV. Both above-mentioned phase transitions are first order and occur simultaneously with significant reduction in volumes. From our calculations, it is found that the planar structure of paracyanogen is made of ten-membered rings consisting of two C-C, four C-N, and four C=N bonds, while each carbon atom has sp2-like hybridization. In the new-formed solid, all the carbon atoms have sp3-like hybridization and all the nitrogen atoms have sp2-like hybridizations with their nearest-neighboring C and N atoms. Our optical calculations show that cyanogen, which is a colorless gas, after above transitions turns to black paracyanogen polymer and then to a transparent solid. We have also used phonon dispersion calculation to show the stability of our predicted three-dimensional carbon-nitrogen system. Furthermore, it turns out that the predicted CN solid with stoichiometry 1:1 has also a good elastic property and a high bulk modulus of 330 GPa.
AB - Using a set of first-principles calculations, we have studied the phase transitions of cyanogen molecules (C2N2) under high pressure. We obtained that at high pressure, cyanogen is transformed to a planar graphitelike structure with metallic property, which is experimentally known as paracyanogen. By increasing pressure, paracyanogen is transformed to an insulator carbon-nitrogen solid with an indirect band gap of 3.2 eV. Both above-mentioned phase transitions are first order and occur simultaneously with significant reduction in volumes. From our calculations, it is found that the planar structure of paracyanogen is made of ten-membered rings consisting of two C-C, four C-N, and four C=N bonds, while each carbon atom has sp2-like hybridization. In the new-formed solid, all the carbon atoms have sp3-like hybridization and all the nitrogen atoms have sp2-like hybridizations with their nearest-neighboring C and N atoms. Our optical calculations show that cyanogen, which is a colorless gas, after above transitions turns to black paracyanogen polymer and then to a transparent solid. We have also used phonon dispersion calculation to show the stability of our predicted three-dimensional carbon-nitrogen system. Furthermore, it turns out that the predicted CN solid with stoichiometry 1:1 has also a good elastic property and a high bulk modulus of 330 GPa.
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U2 - 10.1103/PhysRevB.83.134111
DO - 10.1103/PhysRevB.83.134111
M3 - Article
AN - SCOPUS:79961046629
VL - 83
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
SN - 0163-1829
IS - 13
M1 - 134111
ER -