Hello everyone.

We're doing 'The Solid State' in our school where I first went through the concept of Unit Cells Lattices. Can someone help me through with -

1) Why are there only 14 such lattices?

2) How can one give a rigorous proof about the non existence of unit cells of 'End-centered cubic lattice' and 'face centered tetragonal lattice'.

Thank you!

## Comments

Sort by:

TopNewest2) Even if you put particles on edge centers, it will again form same type of but smaller simple cubic unit cells. And same is the case of face centered tetragonal lattice. – Kushal Patankar · 2 years ago

Log in to reply

– Priyansh Sangule · 2 years ago

Indeed. This is what my teacher explained me. BTW what about the other cases? Do all of them have the same reasoning?Log in to reply

– Kushal Patankar · 2 years ago

May be they exist but , their properties may be similar to one of those 14. And this can be reason for having only 14 bravais lattice.Log in to reply

1 is a bit difficult to show.

For 2, the main idea is that if you did place lattice points at those places, you'd get smaller unit cells as repeating patterns.

I came to know about this from the coursera course on "Symmetry: Beauty, Form and Function"

To begin with, I suggest you look up the Wallpaper Symmetry Groups first.

(by the way, I do not have the full answer to your question) – Agnishom Chattopadhyay · 2 years ago

Log in to reply

– Priyansh Sangule · 2 years ago

Hey, thanks for your views bro! :DLog in to reply

See, both of the things you have asked are based on observations so there is actually no answer. The reason agnishom gave is what I don't know. – Vishal Ch · 2 years ago

Log in to reply

The answer to the first could be that only 14 bravais lattice are seen practically yet. – Naman Kapoor · 2 years ago

Log in to reply

– Agnishom Chattopadhyay · 2 years ago

Nope, they are mathematical structures - not empirically derived structures in chemistry.Log in to reply

– Priyansh Sangule · 2 years ago

You both are somewhat right. They do are mathematical structures but we exclude the ones which are practically not possible.Log in to reply

– Agnishom Chattopadhyay · 2 years ago

Which ones are they?Log in to reply

– Priyansh Sangule · 2 years ago

Like, Edge Centric and other cases...Log in to reply

– Agnishom Chattopadhyay · 2 years ago

As far as my understanding goes, there are no edge centric bravais lattices because inserting lattice points at the midpoint of every edge it instead transform into another kind of Bravais LatticeLog in to reply

– Priyansh Sangule · 2 years ago

Yes. I think this is more appropriate. Thanks!Log in to reply

– Pranjal Jain · 2 years ago

Your understanding is, well, alright as always! \(\ddot\smile\)Log in to reply