1. M. Pomerantz, 1972 Ultrasonics Symp. Proc. p. 479, I.E.E.E. Catalog Number 72 CHO 708-85U, summarizes approximations made in several recent calculations.
2. C. Kittel, Introduction to solid state physics 4 (Wiley and Sons, New York).
3. Lattice Dynamics of Rutile