  We develop an approach to liquid thermodynamics based on collective modes. We
perform extensive molecular dynamics simulations of noble, molecular and
metallic liquids and provide the direct evidence that liquid energy and
specific heat are well-described by the temperature dependence of the Frenkel
(hopping) frequency. The agreement between predicted and calculated
thermodynamic properties is seen in the notably wide range of temperature
spanning tens of thousands of Kelvin. The range includes both subcritical
liquids and supercritical fluids. We discuss the structural crossover and
inter-relationships between structure, dynamics and thermodynamics of liquids
and supercritical fluids.
