1. The problem statement, all variables and given/known data Units of the problem are chosen to be such as KB = 1 and ħ = 1 so that energies are expressed in Kelvin and lengths in Å. The professor says the resulting value of ħ2 / 2 m for a 4-He atom is 6.0599278: how is that possibile? 2. Relevant equations Natural units websites give many conversion factors: https://thespectrumofriemannium.wordpress.com/2013/01/30/log070-natural-units/ http://en.wikipedia.org/wiki/Natural_units 3. The attempt at a solution as the 4-He mass is m ≈ 6 * 10-27 Kg ħ2 / 2 m ≈ 8,4 * 10^-43 m2/s Now using conversions of meters and seconds to eV (given at https://thespectrumofriemannium.wordpress.com/2013/01/30/log070-natural-units/) we find m2/s ≈ 0,0169 so the result is wrong. I tried in many other ways, starting for example from ħ = 1 and converting the 4-He mass, but I cannot find any way to get the result ħ2 / 2 m ≈ 6.0599278 Thank you very much in advance for your help!