What is the main information stored in a .TSDE file?
The .TSDE file stores the TranSIESTA density matrix. If the .TSDE file is found by TranSIESTA, TranSIESTA does not start with a SIESTA self-consistent cycle, it goes directly to a TS cycle, taking the density matrix stored in the .TSDE file as the initial input.
If you erase the .TSDE file, the code starts with a SIESTA SCF cycle, taking as the initial input the density matrix stored in the .DM file.