\begin{equation}
\alpha_\mathrm{iso} = \frac{1}{3}(\alpha_{xx} + \alpha_{yy} + \alpha_{zz})

\alpha_\mathrm{aniso} = \frac{1}{\sqrt{2}}\sqrt{(\alpha_{xx} - \alpha_{yy})^2 + (\alpha_{xx} - \alpha_{zz})^2 + (\alpha_{yy} - \alpha_{zz})^2 + 6(\alpha_{xy}^2 + \alpha_{xz}^2 + \alpha_{yz}^2)}
\end{equation}