Most of our crystal structure models are made to represent approximately 1.3a x 1.3b x 1.3c of the unit cell lengths. Crystal models of that size are the minimum size that (almost) always allows the user to see every atom type in its own unique coordination sphere. By building models of those dimension, we ensure that you get a model that fulfils all that it needs to in terms of illustrating the structure, but without paying for a larger model than you need.
Large crystal structure model of LiFePO4
With some structures - particularly those with a particularly long or short unit cell along one dimension, we will discuss with you how many unit cells displayed. Calcite, for example, would generate a very weak model if we built it to our normal dimensions so, as a matter of course, we tend to build this to a size of at least 2a x 2b x 1.3c.
Sometimes, though, you just want something that blows the viewer away - any model comprising a large number of unit cells will do that in a way that you just have to experience for yourself. When you look down a model and see 'atoms' extending away for some distance, and you see the lines of the various crystal planes, they look stunning. So, if you need something that will really 'wow' your audience, we really recommend this approach.
Large NaCl crystal structure model
We're proud of our giant models and they have a certain kind of impact, but we love our extra large Beevers molecular models - so much so, that it's sometimes genuinely really hard to part with them.
view into a very large (2m tall) model of quartz