IPM approach to Hubbard model. Applications and limitations of restricted CI calculations to ground states of some π networks containing fused 5- and 6-membered rings
✍ Scribed by N. Flocke; T. G. Schmalz
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 283 KB
- Volume
- 76
- Category
- Article
- ISSN
- 0020-7608
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✦ Synopsis
The validity of the independent particle model IPM approach in treating the Hubbard model with uniform hopping parameter t and uniform on-site < < repulsion term U is investigated for several Urt ratios on the ground states of some networks containing fused 5-and 6-membered rings with up to N s 32 electrons. It is Ž . shown that single and double excitation configuration interaction SD-CI based on a closed-shell Huckel-type reference determinant plus a correction added for the size consistency error using appropriate known correction terms leads to sensible estimates of < < the ground-state energy for up to Urt F 4. The IPM approach is hence well suited for < < treating the chemically relevant region of Urt f 1.5 y 2 for systems. The systems studied in this work involve several fullerene-type fragments with up to N s 16, for Ž . which a full configuration interaction FCI calculation is possible, and three larger Ž . Ž . 4y systems, namely Corannulene N s 20 , the C fullerene N s 26 and the C fullerene 26 28 Ž . anion of T symmetry N s 32 , for which only a limited CI involving single, double, d Ž
. triple, and quadruple excitations SDTQ-CI could be performed as a guide. SD-CI calculations on these latter systems further reproduced qualitatively correct charge densities and nearest-neighbor bond orders. Wherever possible, the obtained results were compared with those obtained by different methods present in the literature, based on Monte Carlo approaches. Further we indicated a strategy as to how to perform optimum Ž . FCI HubbardrPariser᎐Parr᎐Pople PPP calculations as far as computation time is concerned.