Stability Mechanism Of High-Pressure Polymeric CO At Ambient Conditions

The high-pressure polymeric CO（denoted as p-CO）exhibits high energy density and stability at ambient conditions.p-CO exhibits similar crystal structures and phase diagrams as an isoelectronic system of polymeric nitrogen.However,compared with the high pressure and temperature required to turn molecular N₂into extend solids,the synthesis of p-CO requires only moderate pressure and temperature（～5 GPa at 300K）.More importantly,p-CO is the only low-Z extended solid that has been successfully recovered to ambient conditions.Therefore,it is of great scientific and technological importance to clarify the stability mechanism of p-CO to develop more low-Z extended solids.In view of the above problems,particle swarm optimization algorithm and potential energy surface stochastic surface walking were used in this dissertation to search the crystal structure and study the stability of CO at high pressure,which provided theoretical support for the experimental synthesis of p-CO materials that could be stable at ambient conditions.We proposed a new target product of p-CO,and studied the physical and chemical properties of different p-CO structures at high pressure,constructed the potential energy surface of p-CO at different pressures,and obtained the following research results:1.The high-pressure structure of CO is predicted by using the first principle method combined with the particle swarm optimization algorithm in CALYPSO.We successfully predicted a p-CO crystal with space group P2₁（CO＿P2₁）at 5GPa pressure,which is intercalated with CO₂molecules between chain five membered lactone rings（C₃O₂＿Cmc2₁）.The phonon spectra,Raman spectra and related physical properties of the structure are calculated and compared with the experimental results.The predicted p-CO crystals are in good agreement with the experimental results.We compared the Raman and infrared spectra of different polymeric carbon monoxides,and the results showed that the experimentally synthesized p-CO may be a mixture of various structures.2.The high-pressure potential energy surface of p-CO at different pressures was constructed by using LASP software based on the stochastic surface walking combined with density functional theory calculation method,and the stable structures at different pressures are identified.The dynamic stability and decomposition path of p-CO products at ambient conditions were theoretically explained.The transition barriers of CO＿Cmca,CO＿P2₁2₁2 and C₃O₂＿Cmc2₁are 124.81 k J/mol,89.02 k J/mol and 155.62 k J/mol,respectively.Finally,the Arrhenius equation was used to calculate the reaction rate and reaction half-life,and the result showed that CO＿Cmca and C₃O₂＿Cmc2₁can exist at 0 GPa.Reaction half-life of p-CO products at ambient conditions are calculated are 1.2×10⁸S（CO＿Cmca）,6.5×10¹S（CO＿P2₁2₁2）and3.1×10¹³S（C₃O₂＿Cmc2₁）.Therefore,CO＿Cmca and C₃O₂＿Cmc2₁can be considered as the stable structures of the recovered p-CO products at the ambient conditions.