Could anyone provide me some materials on the derivation of Ewald's generalized theta function (in English)? The original paper was written in German :-(

Die Berechnung optischer und elektrostatischer Gitterpotentiale

P. P. Ewald

Annalen der Physik

Volume 369, pages 253–287, 1921

http://onlinelibrary.wiley.com/doi/10.1002/andp.19213690304/abstract

(DOI: 10.1002/andp.19213690304)