# Cut-off energy of Be having HCP structure

1. Sep 30, 2016

### Armani

Hello,

I have to calculate the cut-off energy of Beryllium that have hcp structure with the paramters: a=2.29Å and c=3.58Å.

WHAT I HAVE DONE SO FAR:
Using plane (100) or (010)

Since the formula is: $$E=\frac{1}{2} \times G^2$$

$$G=\frac{2 \Pi}{2d}$$

$$\frac{1}{d^2} = \frac{4}{3} \times \frac{h^2+h \times k+k^2}{a^2}+\frac{l^2}{c^2}$$ ---> $$d=1.98 \times 10^{-10}$$
So
$$G= 3.168208497 \times 10^{10}$$
and finally
$$E=5.018772540 \times 10^{20}$$

BUT the SOLUTION says that E=5.22 meV. Can someone correct my calculation?

2. Sep 30, 2016

### Staff: Mentor

Your calculation is missing units. Add them and you'll find your mistake. There is no reasonable energy unit where 1020 would not be way too large.

3. Oct 2, 2016

### Armani

It is not working..maybe I am to confused.

4. Oct 2, 2016

### Staff: Mentor

What is not working? Did you add the units as suggested?