Download the demo version of Chem3D.
Here's example model files for a bunch of crystal structures.
The "Suggested bonding fractions" can be set in the Preferences (View menu, Preferences) in the "Building" pane, the "Bond Proximate Addition (%)" setting. You must make your selection before opening the file, and changing the setting will have no effect on models which are already open.
Chem3D automatically gives different atom species different colors. I use that in these files to color the different types of positions in the cells. For instance, in the Diamond structures, the conventional cell corners are gray, the other FCC lattice points are red, and the added atoms are blue or puce depending on whether they are a basis set with a gray or red atom.
Abbreviations: NN="nearest neighbor", CC="Conventional Cell"
| Several CC | Only one CC | Suggested bonding fraction | Comments | |||
|---|---|---|---|---|---|---|
some NN bonds |
all NN bonds |
CC edges also |
||||
| monatomic basis | BCC | BCC one cell | 45% |
60% |
Ga(llium)(gray) are conventional cell corners, I(odine)(pink) are at the body center. | |
| FCC | FCC one cell | 60% |
70% |
97% |
C(arbon)(gray) are conventional cell corners, O(xygen)(red) are on the face centers, F(luorine)(green) replace some C to give a square base. | |
| FCC | 40% |
C and O are now located on (111) planes, to emphasize the 3-fold symmetry. | ||||
| hexagonal | hex one primitive cell | 45% |
65% |
The plane separation is not determined by the symmetry of the lattice. This example has points closer in the hexagonal plane than in between planes. | ||
| two-atom basis | HCP | 35% |
50% |
C make the underlying hexagonal lattice, F(luorine)(green) are layers in between shifted sideways. | ||
| Diamond | Diamond one cell | 40% |
C are conventional cell, O on the face centers, N(itrogen)(blue) are basis pairs with C, and F are basis pairs with O. Cl(orine)(green) replace some C to give a square base. | |||
| almost Diamond | 15% |
40% |
As above, with N and F shifted slightly towards their basis partners, so that you can show bonds only between atoms in the basis. | |||
Note that these files are simply text files - you could edit them if you want.