Atomic fundamental physical constant used as atomic unit of energy: \(E_{\rm{h}}=\frac{\mathrm{\hslash }^{2}}{m_{\rm{e}}\ a_{0}^{2}} = 4.359\ 7482(26)\times 10^{-18}\ \rm{J}\), where \(\mathrm{\hslash}\) is the Planck constant divided by \(2\ \pi \), \(m_{\rm{e}}\) the electron rest mass and \(a_{0}\) the Bohr radius.