  Calculating liquid energy and heat capacity in general form is an open
problem in condensed matter physics. We develop a recent approach to liquids
from the solid state by accounting for the contribution of anharmonicity and
thermal expansion to liquid energy and heat capacity. We subsequently compare
theoretical predictions to the experiments results of 5 commonly discussed
liquids, and find a good agreement with no free fitting parameters. We discuss
and compare the proposed theory to previous approaches.
