From articles reporting DFT calculations in atomic systems (eg. unit cells of metallic systems), I have seen charts that display contours of the "Electron Density" and "Electron Density Difference". Would appreciate it if someone could give a brief explanation of (1) what the difference between the two is? and, (2) how do I interpret the nature of the bonding in the system from these charts? I'm interested because I am performing DFT calculations, but don't have the benefit of a formal grounding in physics and chemistry ( I come from a mechanical engineering department ...) Just to give a heads-up, I've seen the answer to question 12 in the following URL, but I'd like to know if there's anything fundamental that I should know, or anything that I need to note. http://www.tcm.phy.cam.ac.uk/castep/dftexercises.html In fact, if there's anyone out there who could help interpret these diagrams, please let me know! Any assistance will be acknowledged appropriately!