The unique behavior of the "liquid state", together with the richness of
phenomena that are observed, render liquids particularly interesting for
the scientific community. Note that the most important reactions in
chemical and biological systems take place in solutions and liquid-like
environments. Additionally, liquids are utilized for numerous industrial
applications. It is for these reasons that the understanding of their
properties at the molecular level is of foremost interest in many fields
of science and engineering. What can be said with certainty is that both
the experimental and theoretical studies of the liquid state have a long
and rich history, so that one might suppose this to be essentially a
solved problem. It should be emphasized, however, that although, for
more than a century, the overall scientific effort has led to a
considerable progress, our understanding of the properties of the liquid
systems is still incomplete and there is still more to be explored.
Basic reason for this is the "many body" character of the particle
interactions in liquids and the lack of long-range order, which
introduce in liquid state theory and existing simulation techniques a
number of conceptual and technical problems that require specific
approaches. Also, many of the elementary processes that take place in
liquids, including molecular translational, rotational and vibrational
motions (Trans. -Rot. -Vib. coupling), structural relaxation, energy
dissipation and especially chemical changes in reactive systems occur at
different and/or extremely short timescales.