  Thermodynamics of two-dimensional Yukawa (screened Coulomb or Debye-H\"uckel)
systems is studied systematically using molecular dynamics (MD) simulations.
Simulations cover very broad parameter range spanning from weakly coupled
gaseous states to strongly coupled fluid and crystalline states. Important
thermodynamic quantities such as internal energy and pressure are obtained and
accurate physically motivated fits are proposed. This allows us to put forward
simple practical expressions to describe thermodynamic properties of
two-dimensional Yukawa systems. For crystals, in addition to numerical
simulations, the recently developed shortest-graph interpolation method is
applied to describe pair correlations and hence thermodynamic properties. It is
shown that the finite-temperature effects can be accounted for by using simple
correction of peaks in the pair correlation function. The corresponding
correction coefficients are evaluated using MD simulation. The relevance of the
obtained results in the context of colloidal systems, complex (dusty) plasmas,
ions absorbed to interfaces in electrolytes is pointed out.
