Thanks, Axel. Sorry for the late reply. <div class="gmail_quote">On Sat, Apr 18, 2009 at 3:48 PM, Axel <<a href="mailto:akoh...@gmail.com">akoh...@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im"> </div>those fractional charges could be provided as pseudopotentials. there are DFT codes that allow you to have "fractional hydrogens" to terminate polar surfaces. since cp2k also supports all electron calculations, you could add an all-electron entry with a fractional charge and then define an empty basis set for that atom type.</blockquote><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> however, i would be very careful with a setup of that kind. if the "fractional atom" is too close to other atoms you may get spill-out, and many people that program quantum codes tend to implicitly or explicitly assume that electrons and charges are integer throughout and thus you may get unexpected results and should run careful tests on easy to debug test systems. i am certain that cp2k developers would be happy to get feedback and test inputs on that subject.</blockquote><div> I tried to change the charge of all electron H pseudopotential to a fractional, cp2k complained: an integer type object was expected. So, the present plan is to use H (integer charged) with modified pseudopotential which keeps electrons away. Since the H is just used as counter charge and will not be close to the rest of system, I am not worried about the spill-out of electrons. I am still working on how to modify the pseudopotential of H. If someone knows how to do this, I am greatly appreciated if letting me know. Many thanks in advance. </div> <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> other than that, it might be easier to discuss options, if you could produce an example input illustrating your setup and ideally also an example input for a code that does support what you want to do, or a paper describing such a calculation. </blockquote><div> I am sorry I don't know other codes being able to calculate fractional hydrogens and haven't found a paper doing similar things yet. I will get back to you once I work it out. Cheers, Jun </div></div>