Relative stabilities of small carbon cluster isomers

Relative stabilities of small carbon cluster isomers 

The mechanism of formation of C60 and other fullerenes is a challenging and controversial area of active research. Detailed understanding of the factors which determine the structures and stabilities of smaller carbon clusters is of obvious importance in this regard. As a final example, we give some results of applying DFT to these types of systems. 

One question which has not yet been satisfactorily resolved is the ground state of the C4 molecule. The two candidates are a singlet rhombus structure and a triplet linear form. Table 10 presents relative energies of these two isomers [80], calculated by conventional ab initio and DFT methods using a large orbital basis set, 6-311+G(2df). 

on the other hand, predicts the triplet to be more stable than the singlet by 6 kcal/mol, while B-LYP is in even greater disagreement with G2 theory, predicting a triplet ground state by an amount almost as large HF. In 

There are no conclusive experimental results available for these systems, but given the large disparity with G2, it is evident that in this case both DFT methods, especially B-LYP, are qualitatively incorrect. 

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