On the heat capacity of liquids at high temperatures

Making use of a simple approximation for the evolution of the radial distribution function, we calculate the temperature dependence of the heat capacity $C_v$ of Ar at constant density. $C_v$ decreases with temperature roughly according to the law $\sim T^{-1/4}$, slowly approaching the hard sphere asymptotic value $C_v=\frac{3}{2}R$. However, the asymptotic value of $C_v$ is not reachable at reasonable temperatures , but stays close to 1.7--1.8 $R$ over a wide range of temperatures after passing a " magic " $2R$ value at about 2000 K. Nevertheless these values has nothing to do with loss of vibrational degrees of freedom, but arises as a result of a temperature variation of the collision diameter $\sigma$. \end{abstract}