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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
Author(s) -
Flocke N.,
Schmalz T. G.
Publication year - 2000
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(2000)76:1<83::aid-qua8>3.0.co;2-4
Subject(s) - hubbard model , ground state , fullerene , chemistry , electron , ion , physics , statistical physics , computational chemistry , atomic physics , quantum mechanics , superconductivity
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 | U / t | ratios on the ground states of some π networks containing fused 5‐ and 6‐membered rings with up to N =32 π electrons. It is shown that single and double excitation configuration interaction (SD‐CI) based on a closed‐shell Hückel‐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 | U / t |≤4. The IPM approach is hence well suited for treating the chemically relevant region of | U / t |≈1.5−2 for π systems. The systems studied in this work involve several fullerene‐type fragments with up to N =16, for which a full configuration interaction (FCI) calculation is possible, and three larger systems, namely Corannulene ( N =20), the C 26 fullerene ( N =26) and the C 28 4−fullerene anion of T d symmetry ( N =32), for which only a limited CI involving single, double, 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 FCI Hubbard/Pariser–Parr–Pople (PPP) calculations as far as computation time is concerned. © 1999 John Wiley & Sons, Inc. Int J Quant Chem 76: 83–98, 2000