The Φ 𝜆𝜆 ′ 𝜆 ′′ in Eq. 10, and, by extension, the 𝑃 𝜆 and 𝑃 ̃, are formally temperature independent. The 𝑃 ̃ obtained at 300 and 600 K differ by 1.3 %, indicating that it is not strictly possible to replace the Φ 𝜆𝜆 ′ 𝜆 ′′ with a single value and reproduce the 𝜅 latt exactly over a wide range of temperatures. However, the remarkably small difference suggests the 𝑃 ̃ might also be a useful parameter for comparing materials.