Supercritical carbon dioxide has gradually been becoming an important research subject in the academic field, owing to it has a promising application prospect in the field of extraction, precipitation, thermodynamic cycle and chemical reaction. In recent years, there has deep interests of studying the region near the critical point, a large variation of the physical properties can be detected due to the change of temperature and pressure. With the rapid development of molecular simulation technology, it benefits the traditional experimental methods to study the related physical properties variation of the near-critical region. In order to find out the Widom line range of supercritical carbon dioxide in the near-critical region and the molecular structure characteristics of the liquid-like gas region, molecular dynamics simulation technology and cluster analysis were used to investigate the relationship between variation coefficient and skewness of CO2 density time series with Widom line and liquid-gas-like interval, in the condition of the temperature and pressure range of 300K~350K and 5.5MPa ~ 18.5MPa, respectively. The results show that the Widom line of supercritical carbon dioxide in the near-critical region can be determined by connecting the maximum coefficient of variation of the density time series curve. The Widom line begins to extend along with the critical point until it stops at 350K. The molecular distribution structure of supercritical carbon dioxide liquid-like region and gas-like region can be differentiated by the skewness of the number density distributions. The skewness is positive in the gas-like region and negative in the liquid-like region, and reaches the maximum at the Widom line.
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