A path from Ih to C1 symmetry for C20 cage molecule

Autor: Shoufu Pan, Zhigang Wang, Keyan Lian, Xianhong Fan
Rok vydání: 2005
Předmět:
Zdroj: Journal of Computational Chemistry. 26:1279-1283
ISSN: 1096-987X
0192-8651
Popis: The symmetry of the C 2 0 cage is studied based on the intrinsical relationship among point groups (Bradley, C. J.; Cracknell, A. P. The Mathematical Theory of Symmetry in Solids; Claredon Press: Oxford, 1972). The structure of the C 2 0 cage with I h symmetry is constructed, as are eight other structures with subgroup symmetry. A path from I h symmetry to C 1 symmetry is obtained for the closed-shell electronic state, and the structure with D 2 h symmetry is the most stable on this path. Using the D 2 h structure the correlation energy correction is studied on the condition of restricted excitation space at the CCSD(T) level. We obtain curves on the relation between the orbital numbers and the total energy at the CCSD(T), CCSD, and MP2 level, respectively. The results of these curves obtained from MP2 and CCSD(T) methods have the same tendency, while the results of CCSD gradually diverge with an increase in orbital numbers. When the orbitals used in the calculation reach 460, the total energy is -759.644 hartree at MP2 level and is -759.721 hartree by the CCSD(T) method. From the calculation results, we find that a large basis set can improve the reliability of the MP2 method, and to restrict excitation space is necessary when using the CCSD(T) method.
Databáze: OpenAIRE
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