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yjcmwgk(金币+2,VIP+0): 12-16 08:47
嗯我觉得给电子硬性分配电荷是非常不精确，但是能够简明扼要的说明电子转移的问题，比如谁谁谁是electron donar，谁谁谁是electron acceptor。只是一种分析手段，不影响深层次的东西。
P.S."站在南京燕子矶俯瞰长江，静如处子；绝想象不到，在过去，从夔门到西陵峡，是一段多么惊心动魄的航程。" Yong前辈的这句话很有意境啊。
P.S.2 paste here some word from the help file of MS about interpreting the results from charge analysis:
It is widely accepted that the absolute magnitude of the atomic charges yielded by population analysis have little physical meaning, since they display a high degree of sensitivity to the atomic basis set with which they were calculated (Davidson and Chakravorty, 1992). However, consideration of their relative values can yield useful information (Segall et al., 1996a; Segall et al., 1996b; Winkler et al., 2001), provided a consistent basis set is used for their calculation.
The spilling parameter should be in the region of a few percent or less in order to ensure that the results are reliable. If this is not the case, the number of orbitals in the basis set should be increased with care. If this does not significantly improve the spilling parameter, it may be that atomic orbitals do not provide a good representation of some of the states in the system.
In addition to providing an objective criterion for bonding between atoms, the overlap population may be used to assess the covalent or ionic nature of a bond. A high value of the bond population indicates a covalent bond, while a low value indicates an ionic interaction. A further measure of ionic character may be obtained from the effective ionic valence, which is defined as the difference between the formal ionic charge and the Mulliken charge on the anion species. A value of zero indicates a perfectly ionic bond, while values greater than zero indicate increasing levels of covalency. See Segall et al. (1996b) for more details.
Care should be taken when interpreting the bond order values for small unit cells. The results will be incorrect whenever an atom is bonded to a number of periodic images of itself. For example, bond orders for the primitive cell of silicon are reported as 3.0, while the same calculation for the conventional cell gives 0.75. The factor of four appears because CASTEP sums up the bond orders for the four bonds that link the Si atom at the origin with the periodic images of itself, in the primitive cell. A manual analysis of the multiplicities is required in such cases, specifically: determine the number of bonds to periodic images of the same atom and divide the bond order by that number.
Note: The physical meaning of Mulliken charges or bond populations for metallic systems is unclear. This calculation is allowed, but the scientific interpretation of the results will be left to the user.
[ Last edited by Joannaouc on 2009-12-27 at 15:31 ] |
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顶你，确实很多人没有了解学习理论计算，并且把它应用在很多学科中！