I understand that in a crystal lattice the molecule will tend towards the structure that is the lowest in energy (fcc, hcp, ccp, etc.). How does the molecule find these lowest energy states? Is it possible for a molecule to be caught in a local minima?
closed as too broad by Mithoron, A.K., a-cyclohexane-molecule, Tyberius, Todd Minehardt Sep 20 '18 at 23:37
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The answer is it doesn't. The molecule transfers from state to state, whenever it can get over the excitation energy barrier between them.
Once it lands in the lowest energy state (or a relatively low one), it just has a hard time getting out again. And if the lowest energy state is on the surface of a crystal, the hole gets deeper and the walls get higher the more other molecules (or atoms) arrange themselves around it.
If the arrangement (the crystal lattice) only represents a local minimum, that's likely still quite (=meta)stable. Actually those metastable states tend to be created with a high probablility, see https://en.wikipedia.org/wiki/Polymorphism_(materials_science)#Ostwald's_rule