On Mon, 5 May 2008, O. Baris Malcioglu wrote: BM> Hi, BM> BM> Maybe some details on how you are calculating the system in Gaussian BM> will be helpful, especially the basis set and the X-C functionals. I BM> suspect the problem arises from the intrinsic difficulty of describing BM> Carbon atoms and Lanthanium at the same time using all-electron BM> wavefunctions. You should pay extra attention how your carbon cores are BM> described in a set that is tailored for Lanthanoids, or vice versa.
baris, i beg to differ. there may be basis set completenes issues when using a too small basis set, but why should you need to tailor the carbon basis set for lanthanoids? the whole point of having defined basis sets is, that those _are_ balanced. so that should at most be a minor effect. i would rather expect the differences arising from much more obvious issues. i.e., a) the fact that you have to project your plane wave wavefunction on an atomic basis set and that this projection cannot be complete, since you don't have a complete basis set that you project on. rather you use a minimal basis built from the atomic pseudowavefunctions. you can easily lose 1-2 electrons here. b) as paolo already noted, the differences between different ways to perform the population analysis. e.g. mulliken vs. loewdin vs. nbo vs. ... if you have access to the CPMD (www.cpmd.org) code you can easily see how large those effects can be, as the code allows to project on either atomic pseudo wavefunction or a minimal slater basis (or any gaussian basis you define in the input) as well as it supports mulliken and loewdin like analysis. comparing the dependence of the thusly calculated partial charges from plane waves on the basis set and method is quite educational... (not to mention the impact of pseudopotentials, plane wave cutoff etc...). we are frequently tempted to put too much trust into the many digits of numbers that we calculate. their absolute accuracy can be _much_ less. cheers, axel. BM> BM> O. Baris Malcioglu BM> SISSA CM sector, BM> Trieste, Italy BM> Tel:+390403787374 BM> BM> > On May 3, 2008, at 1:25 , JAIME GUSTAVO RODRIGUEZ ZAVALA wrote: BM> > BM> > BM> >> When analyzing the endohedral La at C60 molecule I BM> >> obtain, using the gaussian03, a charge transfer from BM> >> the La atom to the C60 cage, leaving the La atom with BM> >> a charge of +2.12. However the pwscf charge BM> >> calculation (with the La.pw91-nsp-van.UPF) gives also BM> >> a charge transfer from the La atom to the C60 cage, BM> >> but leaves the La atom with a charge of +1.08. Is this BM> >> a natural difference between gaussian03 (natural BM> >> population analysis) and pwscf (Lowdin analysis)? BM> >> BM> _______________________________________________ BM> Pw_forum mailing list BM> Pw_forum at pwscf.org BM> http://www.democritos.it/mailman/listinfo/pw_forum BM> -- ======================================================================= Axel Kohlmeyer akohlmey at cmm.chem.upenn.edu http://www.cmm.upenn.edu Center for Molecular Modeling -- University of Pennsylvania Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323 tel: 1-215-898-1582, fax: 1-215-573-6233, office-tel: 1-215-898-5425 ======================================================================= If you make something idiot-proof, the universe creates a better idiot.
