Determination of consistent semiempirical one-centre integrals based on coupled-cluster theory

ABSTRACT

We examine the one-centre integrals used in semiempirical molecular orbital theory, for the elements H–Ne. The currently used parameters do not provide good estimates for the relative energies of ionised states of atoms. Directly calculating the one-electron integrals U _ss and U _pp with coupled-cluster theory and fitting the two-electron repulsion integrals G _ss and G _pp to accurate coupled-cluster ionisation curves improves this behaviour. Since all the remaining parameters can be derived from these, the number of fitted variables is reduced from seven to two. The two-parameter model provides qualitative agreement with coupled-cluster theory for all ionisation potentials (IPs) and the principal electron affinity (EA). To obtain quantitative agreement for the principal IP and EA, U _ss and U _pp are included as variables in a four-parameter model. We discuss the new parameters and implications for the development of new, consistent semiempirical Hamiltonians.     

C70O2可能异构体的结构和电子光谱的理论研究＊

用AM1、 PM3及INDO系列方法研究了C     

氮杂及硼杂碳笼的电子结构和光谱研究

用INDO方法研究了氮杂与硼杂碳笼CnX(n=59,69;X=N+,B-)的电子结构和光谱,表明CnX与C60,C70相比将发生结构畸变,氮杂碳笼比硼杂碳笼稳定,C70中靠近极附近的两种C原子易被杂原子置换.本文在对电子跃迁进行理论指认的同时,讨论了光谱红移的原因.     

新型双重电荷转移分子的二阶非线性光学性质的 理论研究

以INDO/SCI方法为基础,按完全态求和(SOS)公式编制了计算分子二阶非线性光学系数β~i~j~k和β~μ的程序。研究了1,2-二氨基-4,5-二硝基苯1和其异构体1,3-二氨基-4,6-二硝基苯2的电子光谱和二阶非线性光学性质。计算表明分子1具有与分子2几乎相等的二阶非线性极化率。但由于分子1的偶极矩明显大于分子2的,故分子1的μβ值比分子2的μβ值大的多。在此基础上,研究了2,3-二(β-苯乙烯基)-5,6-二氰基吡嗪和2,3-二(β-噻吩乙烯基)-5,6-二氰基吡嗪和2,3-二(β-噻吩乙烯基)-5,6二氰基吡嗪衍生物的电子光谱和二阶非线性光学性质。结果表明,这些化合物均具有两个相距很近的强吸收峰,它们对β值的呈加和模式。由于这类化合物特征吸收峰均位于413nm以下且具有大的μβ值,所以,它们是一类很有前途的二阶非线性光学候选材料。     

N－甲基-吡咯烷并[3,4]C60衍生物的结构、电子光谱 和二阶非线性光学性质的 理论研究

利用半经验AM1量子化学方法研究了N－甲基－吡咯烷并[3,4]C60(MPC)及其噻吩取代衍生物(TMPC)的几何结构。电子结构研究表明,MPC及TMPC衍生物的前沿轨道主要由C60部分决定,C60母体与成基团之间存在较强的分子内电荷转移,C60部分是电子受体,而噻吩环部分和吡咯环部分为电子给体。在AM1优化几何构型的基础上,用INDO/SCI方法计算了MPC及TMPC的电子光谱,用完全态求和(SOS)公式计算了其二阶非线性光学性质。结果表明,MPC与TMPC在400nm以上均存在吸收峰,TMPC的这些吸收峰(400nm以上)比MPC的吸收峰强得多,与实验所得结果一致。对于TMPC来说,其二阶非线性光学系数β0值随分子构型不同而有较大的变化,β0值最大可达60×10^-30esu。     

C80n (D2,Ih)的Jahn-Teller畸变和电子光谱

用INDO系列方法研究C80n(D2,Ih)的Jahn-Teller畸变,表明C80(D2)比C80(Ih)稳定,与实验一致;C80n(D2)未发生Jahn-Teller畸变,C80n(Ih)的部分离子发生明显的Jahn-Teller畸变,电荷对C80(Ih)稳定性有显著影响.首次计算其电子光谱,不仅得到C80(D2)与实验一致的吸收峰,还预测了C80n(D2,Ih)的电子光谱,对电子跃迁进行理论指认.C80n(D2)光谱与C80(D2)相比发生吸收峰红移,而C80n(Ih)光谱与C80(Ih)相比发生吸收峰兰移,其原因是C80n(D2)的LUMO-HOMO能隙比C80(D2)小,而C80n(Ih)的能隙则比C80(Ih)的能隙大.     

Quantum chemical investigation on one- and two-photon absorption properties for a series of donor-π-acceptor-type compounds with trivalent boron as an acceptor

In this paper, one- and two-photon absorption properties as well as the transition nature of a series of donor-π-acceptor-type compounds with trivalent boron as an acceptor have been theoretically studied by using INDO/SDCI method. Our calculations indicate that the four o-methyl moieties on the two mesityl groups play an important part in protecting the trivalent boron from being attacked by oxygen in the air. The trivalent boron containing group can be an all-right electron-acceptor with some bulky groups attached to it. On the basis of geometry optimization and UV–vis spectra, the positions and strengths of two-photon absorption for these molecules were reported.     

Electronic properties of thienodiazepine and benzodiazepine derivatives

Summary The structural and electronic characterization of thieno [3,4-b][1,4]-diazepine and 1,5-benzodiazepine systems was carried out by semi-empirical quantum-mechanical calculations. A number of electronic properties were computed and examined in order to study the structure-activity relationship. Theoretical data indicate that the electronic rather than structural properties appear primarily responsible for the variant degree of anticonvulsant activity exhibited by compounds 1–4.     

Waugh-型镍钼杂多酸的量子化学计算

采用半经验INDO法，完成了Waugh-型镍钼杂多酸（NH44）6〔NIMO9O32〕·6H2O的量子化学计算，得到146个成键轨道和78个反键轨道，轨道能级，电荷和键序等数据。通过对这些数据的分析，表明杂多酸分子中端氧和Ni都可能为化学活性中心，各原子轨道在分子轨道中都占有一定比例，其HOMO和LUMO能级皆为负值，其体系具有进一步接受电子的能力。这些结论与实验事实一致。     

A Green's function approach to the photoelectron spectrum of bis(π-allyl)nickel[1]

The vertical ionization potentials of bis(-allyl)nickel (see (1) in Fig. 1) are calculated by means of the Green's function approach within a semiempirical INDO extension to the first transition metal series. The computed ionization potentials are in good agreement with an experimentally deduced assignment. In contrast to earlier theoretical and experimental studies, the 7a _u () level is predicted on top of the levels corresponding to the Ni 3d orbitals. Our approach leads to a complete assignment of the PE spectrum of (1) in the outer valence region.