As already mentioned, one of the most costly problems involved in
performing a QMC calculation on a solid is the evaluation of the
electrostatic interactions between the charged particles in the
system. In this section we introduce the Ewald interaction, which has
become the standard technique for evaluating Coulomb interactions in
supercell QMC calculations. In chapter 
a new
interaction is proposed, which is designed to improve upon the results
obtained with the Ewald interaction.