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2006年06月07日

【期刊论文】The Valence Bond Study for Benzenoid Hydrocarbons of Medium to Infinite Sizes

江元生, Yi Gao, Chun-Gen Liu, and Yuan-Sheng Jiang*

J. Phys. Chem. A 2002, 106, 2592-2597,-0001,():

-1年11月30日

摘要

The ground-state energies of polyacenes and polyphenanthrenes are obtained with the density-matrix renormalization group method from finite up to infinite lengths under the classical valence bond theory. In comparison with the exact valence bond results, numerical errors of retaining various numbers of states are all less than 10-5 J. Meanwhile, the linear equations in terms of the chain length are deduced for the groundstate energies of these two homologous series. And the energy gaps between the lowest singlet and triplet states (S-T gap) are also evaluated. On the other hand, the relative local hexagon energy converges as the chain length increases, and leading to an effective conjugated length of n=12 for polyacene and polyphenanthrene.

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2006年06月07日

【期刊论文】Can the Low-Lying Electronic States of Benzenoid Hydrocarbons Be Described by the Semiempirical Valence Bond Approach?

江元生, Jing Ma, Shuhua Li, * and Yuansheng Jiang*

J. Phys. Chem. A 1997, 101, 4770-4775,-0001,():

-1年11月30日

摘要

The low-lying excited states of benzenoid hydrocarbons with up to 22

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2006年06月07日

【期刊论文】Linear Scaling Local Correlation Approach for Solving the Coupled Cluster Equations of Large Systems

江元生, SHUHUA LI, JING MA, YUANSHENG JIANG

J Comput Chem 23: 237-244, 2002,-0001,():

-1年11月30日

摘要

A linear scaling local correlation approach is proposed for approximately solving the coupled cluster doubles (CCD) equations of large systems in a basis of orthogonal localized molecular orbitals (LMOs). By restricting double excitations from spatially close occupied LMOs into their associated virtual LMOs, the number of significant excitation amplitudes scales only linearly with molecular size in large molecules. Significant amplitudes are obtained to a very good approximation by solving the CCD equations of various subsystems, each of which is made up of a cluster associated with the orbital indices of a subset of significant amplitudes and the local environmental domain of the cluster. The combined effect of these two approximations leads to a linear scaling algorithm for large systems. By using typical thresholds, which are designed to target an energy accuracy, our numerical calculations for a wide range of molecules using the 6-31G or 6-31G* basis set demonstrate that the present local correlation approach recovers more than 98.5% of the conventional CCD correlation energy.

coupled cluster, local correlation, linear scaling, localized molecular orbital

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2006年06月07日

【期刊论文】The Valence Bond Calculations for Conjugated Hydrocarbons Having 24-28 π-Electrons

江元生, JIANWU, YUANSHENG JIANG

Journal of Computational Chemistry, Vol. 21, No.10, 856-869 (2000),-0001,():

-1年11月30日

摘要

A novel algorithm is introduced for coding all Slater determinants in the covalent space with conserved SZ, the z component of total spin S for a classical valence bond (VB) model. It effectively minimizes the search time and the storing space in the central memory of the computer. In cooperation with symmetry reductions based on molecular point group and spin inversion, the VB calculations have been extended to benzenoid hydrocarbons of up to 28 π-electrons that have 4×10 7 configurations. The low-lying states of benzenoids with 24, 26, and 28 π-electrons have been obtained for 62 species. To rationalize the aromaticity of benzenoids in a VB scheme, the resonance energy per hexagon (REPH) is defined. A linear correlation between the REPH and the energy gap of the ground (singlet) state and the first excited (triplet) state for 89 benzenoids is established.

valence bond, conjugated hydrocarbons, coding of Slater determinants, spin-inversion symmetry, aromaticity

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2006年06月07日

【期刊论文】Theoretical study of the lowest π→π* excitation energies for neutral and doped polyenes

江元生, Haibo Ma, Chungen Liu, a) and Yuansheng Jiang b)

THE JOURNAL OF CHEMICAL PHYSICS 123, 084303 2005 ,-0001,():

-1年11月30日

摘要

In earlier theoretical studies, it has been widely noticed that the electron correlation effect played an important role in determining the excitation energies of low-lying π→π* excited states for neutral polyenes and their radical cations and dications. In this paper, neutral and doped polyene oligomers of medium to large sizes are investigated with the Pariser-Parr-Pople model, and the π-electron correlation effect is fully taken into consideration by virtue of the density-matrix renormalization group method. The excitation properties in the polymer limit are also obtained by exponential extrapolation from the finite oligomers. The reasonable agreement of our results with the available experimental observations and advanced ab initio calculations is witnessed. It is also observed that while charge doping can significantly lower the exciting energy, the odd-charged oligomers show lower excitation energies than the even-charged ones.

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    南京大学,江苏

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