  Application of the ion sphere model (ISM), well known in the context of the
one-component-plasma, to estimate thermodynamic properties of model Yukawa
systems is discussed. It is shown that the ISM approximation provides fairly
good estimate of the internal energy of the strongly coupled Yukawa systems, in
both fluid and solid phases. Simple expressions for the excess pressure and
isothermal compressibility are derived, which can be particularly useful in
connection to wave phenomena in strongly coupled dusty plasmas. It is also
shown that in the regime of strong screening a simple consideration of
neighboring particles interactions can be sufficient to obtain quite accurate
estimates of thermodynamic properties of Yukawa systems.
