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【期刊论文】The Ground and Excited States of Polyenyl Radicals C2n-1 H2n+1 (n=2-13): AValence Bond Study
吴玮, Yan Luo, [a], Lingchun Song, Wei Wu, David Danovich, [b], and Sason Shaik, *
J. Phys. ChemPhysChem 2004, 5, 515~528,-0001,():
-1年11月30日
The semiempirical valence bond (VB) method, VBDFT(s), is applied to the ground states and the covalent excited states of polyenyl radicals C2n-1 H2n+1 (n=2-13). The method uses a single scalable parameter with a value that carries over from the study of the covalent excited states of polyenes (W. Wu, D. Danovich, A. Shurki, S. Shaik, J. Phys. Chem. A, 2000, 104, 8744). Whenever comparison is possible, the VB excitation energies are found to be in good accord with sophisticated molecular orbital (MO)- based methods like CASPT2. The symmetry-adapted Rumer structures are used to discuss the state-symmetry and VB constitution of the ground and excited states, and the expansion to VB determinants is used to gain insight on spin density patterns. The theory helps to understand in a coherent and lucid manner the properties of polyenyl radicals, such as the makeup of the various states, their geometries and energies, and the distribution of the unpaired electrons (the neutral solitons).
excited states
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吴玮, Lingchun Song, [a], WeiWu, *, Philippe C. Hiberty, [b], David Danovich, [c], and Sason Shaik
Chem. Eur. J. 2003, 9, 4540~4547,-0001,():
-1年11月30日
One of the landmark achievements of quantum chemistry, specifically of MO-based methods that include electron correlation, was the precise calculation of the barrier for the hydrogenexchange reaction (B. Liu, J. Chem. Phys. 1973, 58, 1925; P. Siegbahn, B. Liu, J. Chem. Phys. 1978, 68, 2457). This paper reports an accurate calculation of this barrier by two recently developed VB methods that use only the eight classical VB structures. To our knowledge, the present work is the first accurate ab initio VB barrier that matches an experimental value. Along with the accurate barrier, the VB method provides accurate bond energies and diabatic quantities that enable the barrier heightto be analyzed by the VB state correlation diagram approach, VBSCD (S. Shaik, A. Shurki, Angew. Chem. 1999, 111, 616; Angew. Chem. Int. Ed. Engl. 1999, 38, 586). This is a proof of principal that VB theory with appropriate account of dynamic electron correlation can achieve quantitative accuracy of reaction barriers, and still retain a compact and interpretable wave function. A sample of SN2 barriers and dihalogen bonding energies, which are close to CCSD (T) and G2(+) values, show that the H3 problem is not an isolated case, and while it is premature to conclude that VB theory has come of age, the occurrence of this event is clearly within sight.
ab initio calculations
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吴玮, Yirong Mo, *, Wei Wu, Lingchun Song, Menghai Lin, Qianer Zhang, and Jiali Gao
J. Phys. Chem. Int. Ed. 2004, 43, 1986~1990,-0001,():
-1年11月30日
conformation analysis
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吴玮, Wei Wu, *, †, §, Lingchun Song, Zexing Cao, Qianer Zhang, and Sason Shaik*, ‖
J. Phys. Chem. A 2002, 106, 2721~2726,-0001,():
-1年11月30日
d was tested by calculating the bond energies of H2, LiH, HF, HCl, F2, and Cl2 as well as the barriers of identity hydrogen abstraction reactions,X·+X'H→XH+X'·(X, X'=CH3, SiH3, GeH3, SnH3, or PbH3). It is shown that VBCIS gives results that are at par with breathing orbital valence bond method. The VBCISD method is better and its results match those of the molecular orbital based coupled cluster CCSD method. Future potential directions of the development of the VBCI approach are outlined.
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吴玮, Wei Wu, †, Sason Shaik, ‡, and William H. Saunders, Jr.*, §
J. Phys. Chem. A 2002, 106, 11616~11622,-0001,():
-1年11月30日
Valence bond SCF calculations have been carried out on identity proton transfers of the type X-H + X-→X- + H-X and X-H+ + X→X + X-H+ for systems where X=F-, Cl-, Br-, OH-, SH-, NH2-, PH2-,CH3-, SiH3-, OH2, NH3, and PH3. A hybrid consisting of three contributing structuressreactantlike, productlike, and ionic (X- H+ X- or X H+ X)-gives reasonable results, though additional structures afford a slight further decrease in energy. Energies somewhat below Hartree-Fock and reasonable weights are obtained. Calculated barriers agree well with those obtained by high-level ab initio calculations with correlation. Insights into the factors determining barrier height are obtained.
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