Easiest to use are Quantum Espresso to do the calculation, a detailed tutorial on how to do this can be found here. And the plotting program we'll be using is Xcysden, if you run an arch based distro there's an AUR package for this which needs some tinkering to fully install. I made a tutorial here if you'd like.
After doing the mentioned simulation on the website and getting a .cube file (or if you choose filetype 5 a .xsf file which will also work) go ahead and open it in Xcrysden (cube: file>open structure>gaussian cube thing, xsf just file>structure>xsf). After this you'll just have the unit cell, to view the charge density go to tools>data grid and click ok for the data grid. Now you get a menu for the isovalue, choose a small isovalue and hit submit. You can then also go to a plane number and select some color basis and check some boxes and hit submit.