Cut-off energy of Be having HCP structure

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Armani
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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?
 
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I moved your thread to our homework section.

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.
 
It is not working..maybe I am to confused.
 
What is not working? Did you add the units as suggested?
 
To solve this, I first used the units to work out that a= m* a/m, i.e. t=z/λ. This would allow you to determine the time duration within an interval section by section and then add this to the previous ones to obtain the age of the respective layer. However, this would require a constant thickness per year for each interval. However, since this is most likely not the case, my next consideration was that the age must be the integral of a 1/λ(z) function, which I cannot model.
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