Cut-off energy of Be having HCP structure

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The discussion focuses on calculating the cut-off energy of Beryllium with a hexagonal close-packed (hcp) structure using specific parameters. The initial calculations yield an energy value of approximately 5.018772540 x 10^20, which is significantly higher than the expected value of 5.22 meV. A key issue identified is the omission of units in the calculations, leading to an incorrect result. Participants emphasize the importance of including units to resolve the discrepancy. The conversation highlights the need for careful attention to detail in scientific calculations.
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?
 
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