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1

How can one quickly identify suspicious water molecules that might have been modelled wrong - or what one should be looking for if one suspects a particular water molecules to be something else. You can check how many ligands the water has, and what the distances are. Most water molecules can safely be ignored, except for ones in an active site or so. When ...


3

Whether to use a centered cell or the smaller primitive cell is a question of convention. The conventions are guided by making life easy. You could take a primitive triclinic cell and redefine the cell axes and lengths to make it body-centered but that would be kind of silly. There is no gain in simplifying symmetry operations, and you just made your cell ...


4

Essentially, certain combinations of the possible point-group symmetries (cubic, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic, triclinic) and possible translational symmetries (simple, base-centered, face-centered, body-centered) end up having identical overall lattice symmetries and thus you don't get $7×4$ unique lattices. For example, suppose ...


6

With HCP, things get hairy pretty quickly. This is the first coordination sphere, with 12 atoms at the distance $a$ from the origin: These are the second nearest neighbors, i.e. the 6 atoms at $\sqrt{2}a$ from the origin, each touching 4 atoms of the first sphere: These are the third nearest neighbors, which are the 2 atoms at $\sqrt{8\over3}a$ from the ...


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