where ω l is the average frequency, V is the unit cell volume, x l is the average quantum vibrational number, ϵ s is the static dielectric constant, ϵ ∞ is the high frequency dielectric constant, and R p is an overlap integral. This assumes the excited electron to be uniformly distributed across the entire F-centre. Huang & Rhys noted that when plotting the ratio of internal conversion to fluorescence (Figure ), the dominance of internal conversion is exponentially related to temperature except for higher temperatures, while at temperatures of ∼100 K internal conversion becomes the submissive mechanism by at least a factor of a thousand. In term of internal conversion in modern semiconductor physics, much of the early behaviour was described using the Shockley-Read-Hall model , in which internal conversion is reinterpreted as a trapping mechanism. Generally, one can use the conventional Fermi's Golden Rule formalism (Equation ) to describe internal conversion in the solid state. However, the direct formalism to calculate the coupling term can be adapted from the Shockley-Read-Hall model. One such method is the adiabatic approximation , whereby the initial and final states are described entirely by the Born-Oppenheimer approximation. Lin & Wang calculated the rate for gallium nitride semiconductor blocks, but found their results compared poorly to experiment. The coupling can also be considered in terms of a singular collective of phonon modes alongside the transition degrees of freedom. This one-dimensional quantum formula represents the atomic degrees of freedom through a generalised configuration rather than a specific one.