Why is HCP more common than FCC in elemental compositions?

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HCP is more prevalent than FCC in elemental compositions, particularly among Lanthanoids and Actinoids, despite both structures having the same packing fraction of 74%. The discussion highlights that the distribution of HCP versus FCC elements is nearly equal when excluding these two groups. The reasons for HCP's dominance are not intuitively clear and are suggested to be rooted in quantum mechanics. This complexity indicates that the preference for HCP in certain elements may involve deeper atomic interactions and stability considerations. Understanding these patterns requires further exploration of the underlying quantum mechanical principles.
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This may be obvious but since the packing fraction for both hexagonal close packed and face centered cubic is the same (74% i believe) why is HCP more common in elemental compositions?
 
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Well, I don't really know, but I noticed that a lot of the Lanthanoids and Actinoids are HCP, and if you exclude those two sections, the number of HCP and FCC elements are almost the same.

This is the sort of question that I doubt there is an intuitive answer to...it's all quantum mechanics!
 
Thread 'Unexpected irregular reflection signal from a high-finesse cavity'

Thread 'Unexpected irregular reflection signal from a high-finesse cavity'

I am observing an irregular, aperiodic noise pattern in the reflection signal of a high-finesse optical cavity (finesse ≈ 20,000). The cavity is normally operated using a standard Pound–Drever–Hall (PDH) locking configuration, where an EOM provides phase modulation. The signals shown in the attached figures were recorded with the modulation turned off. Under these conditions, when scanning the laser frequency across a cavity resonance, I expected to observe a simple reflection dip. Instead...
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