# User Guide to Semiempirical Tight Binding¶

This user guide focuses on the semiempirical quantum mechanical methods GFNn-xTB, their descendants, and corresponding composite schemes as implemented in the xtb (extended tight binding) program package.

We provide a number of detailed guides dealing with common task that can be performed easily with the xtb program. All guides are usually structured the same way, starting with some simple examples using only the commandline and the default settings followed by a trouble shooting section. Detailed inputs are provided in a ready to use fashion to solve some more special but still common tasks with xtb together with some insights into the theory used behind the scences.