[DFTB-Plus-User] SK files order sensitivity

[Linwei]

Dear users and developers,

The manual says to run calculation with more than 1 element, the SK file 
of both order (e.g. Zn-O and O-Zn) are needed, but from the format of SK 
files, I don't see why they should be different from each other. I 
checked Zn-O and O-Zn pair from znorg set, and find the matrix part is 
different, which I don't understand. I have also checked H-F and F-H 
pair from 3ob set, they appears to be the same file.

I have also tried to rename and replace one of the file, to make both 
file the same, when doing so with ZnO pair, it messed up the band 
structure. (both two Zn-O.skf and two O-Zn.skf situations will make the 
band structure to go wrong).

Does anyone know the reason for the two files to be different?

Sincerely,

Linwei