This actually isn't a comment for here, but for lines just above:
```
and where we have adopted the convention that grid points at a given `k` represent the
interval between `k - Delta k` and `k + Delta k` (noting that the grid spacing `Delta k` in
k space is equivalent to `kmin`).
```
Am I reading this wrong, or does it suggest as it stands that each grid point covers an interval of width 2 * Delta k?