# Units (Energy)

## eV and cal
$1$eV = $1.6\times 10^{-19}$ J

$1$J = $0.24$ cal

Therefore,
$1$eV = $1.6\times 10^{-19}$ J = $0.384 \times 10^{-19}$ cal.

If the number of pariticle is 1 mol, then
$0.384 \times 10^{-19} \times 6 \times 10^{23}$ cal/mol = 23 kcal/mol.
Thus, a paritical that its energy is 1eV, is eqiuvalent to 23 kcal/mol.
\begin{eqnarray}
1\mathrm{eV} = 23 \mathrm{kcal/mol}
\end{eqnarray}

## Hartree and cal
1Ha = 27.2eV
Thus,
\begin{eqnarray}
1\mathrm{Ha} = 620 \mathrm{kcal/mol}
\end{eqnarray}
\begin{eqnarray}
1\mathrm{mHa} = 0.6 \mathrm{kcal/mol}
\end{eqnarray}