crystal structures question

[darkelf]

Hello, can anyone help me out the the relationship of the atomic radius R with the lattice parameter a for a Hexagonal close packed cystals (HCP) and how to prove the ratio of a:C is 1.633.

Any information on this issues would be appreciated. Thanks

[Gokul43201]

This should get you going: http://physicsforums.com/showpost.php?p=1176371&postcount=2

If you have any trouble, show what you've done and which part you are stuck at, and someone will help you from there.