  It is shown that the isochoric heat capacity of dense gas, fluid and liquid
decreases with increasing temperature at arbitrary values of a density for many
pair interaction potentials, including bonded potentials; that a decrease of
the isochoric heat capacity of the liquid with increasing temperature is
related to a decrease of the interaction between the particles with increasing
temperature; that a radial distribution function for nonideal dilute gas, which
is independent of density, can describe a temperature dependence of the
isochoric heat capacity of liquid argon; that a radial distribution function
dependent on the density and temperature describes a temperature dependence of
the isochoric heat capacity of liquid and dense fluid; that the
Carnahan-Starling equation of state for soft spheres gives a good quantitative
description of the isochoric heat capacity of argon; that the fluctuations of
the kinetic energy increases with temperature faster than that of the potential
energy; and finally, that a liquid state can be considered as a state of dense
gas. The explicit expressions to define the Frenkel line on the (temperature,
density) plane are derived.
