I optimized endohedral fullerene Li@C20 using DFT/B3LYP in Gaussian 09. 6-31G++(d,p) basis set was used in calculations. Total energy of structure is correct and there is the same information in literature about it. But charge distribution analysis shows unrealistic results which don't consist with the results of other researchers. Mulliken charges on carbon atoms are in range from -0,61 to -0,89 and charge on lithium atom is 15,74. What can cause such unrealistic result and how can it be solved?
Mulliken charges have no meaning whatsoever as charges. I believe it is not worth of going after the reason for that. If you are interested in charges for atoms, I suggest using QTAIM. If you have issues against QTAIM, at least Hirshfeld or ADCH, these have advantages compared to mulliken and NPA. Chelpg usually works fine but not for buried atoms as this one.
Wagner E Richter. Thank you for the answer! I will try to use models you recommend for calculations of charges.
Please check: A. J. Stasyuk*, M. Solà* and A. A. Voityuk*. Charge assessments on the encapsulated fragment. Case of endohedral borospherenes. Sci. Rep., 8 (2018) 2882, DOI: 10.1038/s41598-018-21240-0. Open Access.
Dear Anwesh Pandey
, it is worth mentioning that although NPA is widely regarded as a 'reliable' method (in your words), it does not satisfy the molecular dipole moment from the wavefunction. In fact, the expression "dipole moment" does not appear a single time in NPA original paper (Weinhold, 1985). Personally, I wouldn't say I like NPA charges for this reason. There are people rationalizing bond polarity using NPA charges, which makes no sense to me as they do not correlate to dipole moments. There are plenty of other methods superior to NPA for such tasks related to polarity.
B3LYP is not appropiate for electron transfer in Li@C20 due to the self interaction error. You can try wb97X-D, CAM-B3LYP or the other range-separated functionals
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