Hello Diana, As far as I'm aware, SIESTA doesn't print the reciprocal lattice vectors by default and no keyword exists to print them. However, it is relatively easy to create a short script in python or Matlab or such a program that will calculate them by inputting the unit cell vectors and then taking cross products (http://www.lcst-cn.org/Solid%20State%20Physics/Ch22.html) or, if you're ambitious, you can modify the code to print them in a new file or something.
Regards, *Abraham Hmiel* Katherine Belz Groves Fellow in Nanoscience Xue Group, SUNY College of Nanoscale Science and Engineering http://abehmiel.net/about
