# What is electrical conductivity divided by scattering time in DFT calculations?

In DFT calculations, I see many graphs showing electrical conductivity divided by scattering time $$\sigma/\tau$$. But it is treated as electrical conductivity in the papers. What does this mean and why do they plot like this?

• Please don't use abreviations, instead write the complete notions. Abreviations can lead to ambiguities as they can have different meanings in different contexts. Feb 19, 2020 at 14:48
• @FredericThomas DFT is perfectly fine. It would be unreasonable to ask the user to define it (look at the tags by the way!). This question would probably get an answer quite enthusiastically on the brand new Materials.SE: materials.stackexchange.com Jul 23, 2020 at 18:24

Density Functional Theory cannot calculate the scattering time $$\tau$$. That is a parameter that must be experimentally determined from the width of the Drude peak in optical conductivity (the frequency dependence of the AC conductivity).