# Talk:Diamond cubic

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## Greater clarity

The article describes the positions of atoms in a unit cell as follows:

Atomic placement in unit cell of side length a is given by the following placement vectors.

$\mathbf{r}_0 = \vec{0}$

$\mathbf{r}_1 = (a/4)(\hat{x} + \hat{y} + \hat{z})$

$\mathbf{r}_2 = (a/4)(2\hat{x} + 2\hat{y})$

$\mathbf{r}_3 = (a/4)(3\hat{x} + 3\hat{y} + \hat{z})$

$\mathbf{r}_4 = (a/4)(2\hat{x} + 2\hat{z})$

$\mathbf{r}_5 = (a/4)(2\hat{y} + 2\hat{z})$

$\mathbf{r}_6 = (a/4)(3\hat{x} + \hat{y} + 3\hat{z})$

$\mathbf{r}_7 = (a/4)(\hat{x} + 3\hat{y} + 3\hat{z})$


No explanation is given for what the $\hat{x}$, $\hat{y}$, or $\hat{z}$ mean.

Just in case they represent standard unit basis vectors, wouldn't it be a lot clearer if the article presented the coordinates of the atoms in a unit cell of side length = 1, without inventing mysterious symbols for the unit basis vectors? Also, they could be ordered in an organized manner. The list of points would then be as follows:

( 0, 0, 0),

(1/4, 1/4, 1/4),

(1/2, 1/2, 0),

(1/2, 0, 1/2),

( 0, 1/2, 1/2),

(3/4, 3/4, 1/4),

(3/4, 1/4, 3/4),

(1/4, 3/4, 3/4).

Daqu (talk) 06:23, 2 April 2008 (UTC)

## Citations

This article has a good information and it is well written, but it should have some citations. A text book would probably be ideal for this material, although a web source or online publication would do as well.128.97.68.15 (talk) 17:14, 18 July 2008 (UTC)

It's too self-serving for me to add myself, but:
uses this structure. I also have some talk slides for this paper, including a description of the diamond cubic, here. I searched for other descriptions of this structure to cite both here and in my paper without much success. —David Eppstein (talk) 23:59, 26 September 2008 (UTC)
To be more specific, this paper gives the structure mathematical coordinates in four dimensions that are nicer than the three-dimensional coordinates (they are just the integer points whose coordinates add to zero or one, with two points adjacent when they are at unit distance apart) and describes how to project these four-dimensional points down to 3d to get the more familiar form of the diamond structure. It also shows that, because of this 4d structure, the diamond cubic forms an infinite partial cube. —David Eppstein (talk) 23:19, 15 March 2011 (UTC)

## Incorrect information

In the first paragraph, it says that "silicon/germanium alloys in any proportion" follow the diamond structure. That's not accurate. The overall positions of atoms may be the same as in the diamond structure, but if the atoms are not all the same, the structure is different. For example, with a 50-50 ratio, the material could be the zinc-blende structure. Diamond and zinc-blende do not share the same space group, as this article would imply. — Preceding unsigned comment added by Johncolton (talkcontribs) 00:11, 31 December 2010 (UTC)