High-pressure structures of helium and carbon dioxide from first-principles calculations

A systematic computational study on the structural, electronic, and bonding properties of He-CO2 system has been performed using plane wave pseudopotential method based on density functional theory. No stable compound has been found at lower pressures, indicating He is a good protector and quasihydrostatic pressure medium for high-pressure study of CO2. At higher pressures, only one unexpected compound HeCO2 is predicted to be stable at pressure above 448 GPa HeCO2 is a wide band gap insulator with band gap of 5.7 eV. The helium atoms have very weak interaction with the nearest oxygen atoms in HeCO2. Lone pair 2p electrons of oxygen are very important for the stability of HeCO2 phase. The lone pair O_2p electrons make the helium atoms into the interstitial region of two neighboring CO2 polymerized layers.