Dear Fatima,
about the exciton wavefunction, please have a look to this
thread:
and also
this one.
Other users experienced your same problem, and they were using an old version of the code. If this is the case you can also try to compile the 3.3 downloaded by the svn repository, even if I suggest you to try to compile the 3.4
Anyway, unfortunately as reported in the yambo download page and homepage it is not possible to download the code for technical problem. We hope that they will be solved soon.
About the compilation, please try to recompile your code after doing a
make clean_all
Next, if the error persist, please post your config.log file in the yambo directory and in the ./lib/libxc as well.
Moreover tell us on what of machine you are trying to install the code.
Regards,
Daniele