Update 11_nearly_free_electron_model.md - typo

src/11_nearly_free_electron_model.md

@@ -58,7 +58,7 @@ Bloch theorem is extremely similar to the ansatz we used in [1D](7_tight_binding
 
 ## Nearly free electron model
 
-In the free electron model, the dispersion is $E = \hbar^2 |\mathbf{k}|^2/2m$ and the corresponding eigenfunctions $|\mathbf{k}\rangle$ are plane waves with a real-space representation $\psi=\langle\mathbf{R}|\mathbf{k}\rangle= e^{i\mathbf{k}\cdot \mathbf{R}}$. We note that in the free electron model,
+In the free electron model, the dispersion is $E = \hbar^2 |\mathbf{k}|^2/2m$ and the corresponding eigenfunctions $|\mathbf{k}\rangle$ are plane waves with a real-space representation $\psi=\langle\mathbf{r}|\mathbf{k}\rangle= e^{i\mathbf{k}\cdot \mathbf{r}}$. We note that in the free electron model,
 
 * there is only one band
 * the band structure is not periodic in $k$-space