I performed the opt + freq in xtb using the following keyword: ''--ohess --alpb water" the optimization ran fine with NO message like this one:

########################################################################

# WARNING! Some non-fatal runtime exceptions were caught, please check:

# - Hessian on incompletely optimized geometry!

########################################################################

So i thought that my structure was correctly optimized, but when I open the g98.out file i noticed a small negative frequencies, so should I reoptimized my compound or is this a numerical issue ?

Thanks

Alessio