Plotting PotDens only for a certain area in the unit cell
@alek asked for a way we could implement an option to plot only a cutout of the unit cell density/potential.
Why is this feature needed?
Especially for vector plots. They get visually crowded incredibly fast and XCrysDen has to create an artificial atom for each vector. Having a "zoomed in" perspective that only deals with a number of points in an interesting region might be quite insightful.
Naive approach: Define additional plot input that corresponds to a set of fractions of the unit cell vectors. These mark down the only area that should be plotted. However, this would then give only a certain subset of points in the formerly defined full grid, making the computation way more costly than it needs to be.
Another way would be to directly have the scales acting on the loop boundaries and therefore making the grid denser or putting them into the translation between grid integer and real space vector in the cell. The latter way would be the most sensible but we should think about it properly once.
Possible problems and limitations
I guess for potential densities (--> false color plots) this will be not as easy. I think XCrysden expects a "full" surface of values in a rectangular form, so it can be plotted as a slice in the unit cell. The values we provide for this case do not come with a coordinate, while the vector plot values do. So maybe this idea is overall only applicable to vectorplots.