Frenkel anomaly on co-ordination numbers in liquid CO2 at 100 and 1000 bar studied by Monte Carlo simulation using Kihara potential model

An issue concerning the Frenkel line of liquid CO2 is that its location has not been unequivocally determined. So far, reliable Frenkel lines were identified from velocity autocorrelation functions (VAFs) computed by Molecular Dynamic simulations; however VAFs cannot be directly verified experimentally. By contrast, the co-ordination numbers (CNs) can be measured experimentally by X-ray and neutron scattering or computed by Monte Carlo (MC) simulation, and thus provide an alternative means of determining the location of the Frenkel line. In the present study, the CNs were computed by MC simulation using the Kihara potential, and the Frenkel anomalies were identified at {P = 100 bar, T = 260 K}, in good agreement with previous results based on VAFs, and at {P = 1000 bar, T = 370 K}, which deviates significantly from them.