  We study a model of dyons for SU(2) Yang-Mills theory at finite temperature T
< T_c, in particular its ability to generate a confining force between a static
quark antiquark pair. The interaction between dyons corresponds to a long-range
1/r potential, which in naive treatments with a finite number of dyons
typically gives rise to severe finite volume effects. To avoid such effects we
apply the so-called Ewald method, which has its origin in solid state physics.
The basic idea of Ewald's method is to consider a finite number of dyons inside
a finite cubic volume and enforce periodicity of this volume. We explain the
technicalities of Ewald's method and outline how the method can be applied to a
wider class of 1/r^p long-range potentials.
