The model of compound oscillators, each of which consists of four identical linear harmonic oscillators, is used for the description of the pressure variation of the optical rotary power of a quartz. This model establishes the contribution of the interaction of the oscillators not only arranged along the Z axis but also those lying in the neighboring chains.
V. VYšíN and V. JANKů, "Pressure Variation of the Optical Rotatory Power of α Quartz," J. Opt. Soc. Am. 61, 770-772 (1971)