Hi Sungjong,
yes, Mulliken populations are very basis-dependent and (ideally) should
not be used at all for the analysis of charge transfer.
Some fast results could be gained with Andrei Postnikov's sphere charge
integration, but again this one is very radius dependent.
More reliable values could be obtained using Bader analysis
http://theory.cm.utexas.edu/bader/
http://theory.cm.utexas.edu/forum/viewforum.php?f=1
Although, there are problems with calculating Bader populations for
pseudopotential calculations and some fixes are needed for SIESTA to
work with it. I have some code for SIESTA to do it. But for H-containing
compounds the fix is very artificial.
Sincerely,
Alexander.
