PWscf is released under the GNU General Public License.

We shall greatly appreciate if scientific work done using this code will contain an explicit acknowledgment and a reference to the PWscf web page.

Our preferred form for the acknowledgment is the following:

Acknowledgments ...

Calculations in this work have been done using the PWscf package [ref]....

Bibliography

[ref] S. Baroni, A. Dal Corso, S. de Gironcoli, and P. Giannozzi, http://www.pwscf.org.