Physical meaning of the Ewald sum method
  The electrostatic potential and energy of point charges in a real crystal, in the presence of thermal vibrations, is obtained as a special case of the Fourier method. Incorporating the role of thermal vibrations in electrostatic energy calculations leads to the physical meaning of the Ewald sum method. The Ewald summation method determines the electrostatic potential and energy of point charges in a crystal at a temperature that is obtained from the width of the Gaussian and not at 0 K. For values of the width of the Gaussian commonly recommended for computational convenience temperatures exceed 10000 K. 
T. R. S. Prasanna
cond-mat.mtrl-sci