Close-packing models (part 1)

Many metals have either a hexagonal or cubic close-packed structure. To illustrate how this structure is made up, I constructed models in which the two or three different close-packed layers, in hexagonal and cubic close-packed structures, respectively, are displayed in different colours. The models are created using “Balls and Sticks” (see this post). In order to obtain these colours, a different, larger unit cell must be used instead of the conventional cell, and two different elements are needed in the case of HCP, or three in the case of CCP. I used Mg, Co and Ti to obtain the colours in these images. The images above are obtained by increasing the values of the “boundaries” in the x, y and z directions so that the unit cell is repeated. Models for the structures above can be obtained in the Balls and Sticks native file format here: or in the universal CIF file format (which can be opened with other programs) here: You can use the same type of procedure (with a much more complex and larger unit cell in the z-direction!) to produce models of  ccp-hcp martensitic transformation and twinning: Advantages of Balls and Sticks are that it is easy to to learn and produces high-quality, aesthetically pleasing graphics. However, it lacks certain functionality that is provided by other programs such as VESTA (of which more later).