Examples of Structure Optimizations

2 Examples of Structure Optimizations. - In principle, density-functional calculations give exact information on the total energy, for instance as function of structure, and, therefore, they should be able to give exact information on structure. However, due to the introduction of approximate density functionals 

and the C-C-C bond angles 123°,29,30 which agree well with our values. These results support the conclusion above that density-functional calculations can provide accurate information about carbon-carbon bonds in conjugated systems. 

One may repeat this analysis considering many other systems, but the general trends will not change. Therefore, we shall here only consider two further examples, this time from the other end of the periodic table. 

Li and Bursten32 studied the protactinocene Pa( 4-C8He)2 which consists of the Pa atom sandwiched between the two CeHe rings. In this case it is important to include relativistic effects, which was done by the authors. The results (see Table 3) show somewhat larger scatter for the individual parameters, although in no case there are severe deviations. 

Finally, Hay and Martin33 studied the actinide compounds UF6, NpF6, and PuFe. Also in this case the results (Table 4) show that the density-functional calculations produce results that are in good agreement with the experimental results, which also is the case for the Hartree-Fock methods. 

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