AuX (X=O,S)低电子态的理论研究

通常要用多参考态方法才能合理处理需考虑旋轨耦合（SOC）效应的开壳层分子如AuO和AuS的低电子态. 事实上,通过选取合适的参考态,采用运动方程耦合簇方法（EOM-CC）也能计算这些分子的一些低电子态,而且EOM-CC方法是单参考态方法,使用起来比多参考态方法更加简单. 本文采用最近发展的含旋轨耦合的EOM-CC 计算电离能的方法（EOMIP-CC）,选取对应的负离子为参考态,在CCSD 级别上计算了AuO 和AuS低电子态的性质. 在不考虑旋轨耦合时,通过比较EOMIP-CCSD和EOMIP-CCSDT的结果考察EOMIPCCSD的精度. 此外,与EOMIP-CCSDT结果相比,如果自旋污染较为显著而且T₁的模较大时,UCCSD（T）方法对能量最低的某一特定对称性的电子态的所对应的电离能误差约为0.1-0.15 eV. 在考虑了旋轨耦合效应后,我们的方法得到的键长和振动频率与实验值吻合较好. 另一方面,虽然EOMIP-SOC-CCSD高估了能量较高的²Δ_3/2态、²Σ_1/2⁺态和²Π_1/2态的能量,但是对于其它能量更低的电子态,它们的能量与已有实验值误差在0.2 eV 左右. 这显示我们所用的含SOC的EOMIP-CCSD方法对原本需要用多参考态方法才能处理的AuO和AuS低电子态能给出可靠的结果.     

硫族铅化物阳离子低电子态的理论研究

采用我们最近发展的含旋轨耦合的运动方程耦合簇计算电离能(EOMIP-CC)方法,在CCSD级别上计算了硫族铅化物PbS、PbSe、PbTe阳离子低电子态的平衡键长和谐振频率以及绝热和垂直电离能,得到的结果与已有的实验值吻合较好.不考虑旋轨耦合(SOC)的情况下通过与CCSD(T)的计算结果比较,考察了三重激发对计算结果的影响,结果显示考虑三重激发的贡献后得到的键长和频率结果与实验值吻合更好.计算结果表明PbTe+中2Π态的能量分裂明显大于PbS+和PbSe+中2Π态的能量分裂,但是PbTe+中2Π1/2和2Σ1/2态之间的相互耦合则明显弱于PbS+和PbSe+中这两个态之间的耦合.PbTe+中2Π1/2和2Σ1/2态之间耦合很弱,一方面是因为2Σ+态和2Π态的能量差比PbS+和PbSe+中2Σ+态和2Π态的能量差大,另一方面还由于PbTe+中2Π1/2和2Σ1/2态之间的旋轨耦合矩阵元只是PbS+和PbSe+中2Π1/2和2Σ1/2态之间的旋轨耦合矩阵元的一半.这些计算结果为PbS+、PbSe+、PbTe+阳离子的低电子态性质提供了新的理论数据,可以为将来的实验数据提供参考.     

理论研究BrCl~ 低激发电子态势能曲线和光谱性质

应用量子化学中高等级的多参考组态相互作用方法计算了环境科学中重要的分子离子BrCl 的基态和低激发态的势能曲线与光谱常数,详细分析了旋轨耦合作用对电子结构和光谱性质的影响,确认了基态X2Π和低激发电子态的多组态特征,得到了基态X2Π的旋轨耦合分裂能1814cm-1,与实验值2070cm-1接近.预测了2Π(Ⅱ)态的旋轨耦合分裂能为766cm-1.估算了3/2(Ⅲ)-X3/2和1/2(Ⅲ)-1/2(Ⅰ)跃迁的偶极跃迁矩和Frank-Condon因子,讨论了它们的跃迁辐射寿命.     

理论研究BrCI^＋低激发电子态势能曲线和光谱性质

应用量子化学中高等级的多参考组态相互作用方法计算了环境科学中重要的分子离子BrCl^＋的基态和低激发态的势能曲线与光谱常数,详细分析了旋轨耦合作用对电子结构和光谱性质的影响,确认了基态X^2П和低激发电子态的多组态特征,得到了基态X^2П的旋轨耦合分裂能1814cm^-1,与实验值2070cm^-1接近。预测了^2П（Ⅱ）态的旋轨耦合分裂能为766cm^-1。估算了3／2（Ⅲ）-X3／2和1／2（Ⅲ）-1／2（I）跃迂的偶极跃迁矩和Frank-Condon因子,讨论了它们的跃迁辐射寿命。     

等电子三原子铀化物OUO2+、NUN和NUO+的结构和谐振频率的CCSD(T)计算研究

用小核相对论有效势和CCSD(T)方法计算了三原子铀化物OUO²⁺, NUN和NUO⁺的平衡键长和谐振频率. 计算结果显示U原子内层5s5p5d 电子相关能对这些化合物性质的影响非常小. 除NUN的弯曲振动频率,旋轨耦合效应对这些化合物的结构和频率的影响并不明显. 本文的计算结果与其他研究组的计算结果以及已有的实验值相比符合较好, 这表明作为单参考态方法, CCSD(T)能够对这些体系的键长和频率给出较精确的计算结果. 与此前密度泛函理论(DFT)的计算结果相比, CCSD(T)方法与PBE0泛函的结果吻合最好. 本文的工作有助于在用密度泛函方法研究这些体系时选择合适的交换相关泛函, 也为今后的实验研究提供了新的理论数据.     

Nb_3X_4(X=S,Se,Te)的能带结构研究

固相过渡金属原子簇化合物Nb_3X_4(X=S,Se,Te)在低温下出现超导行为,且从S到Te,Nb_3X_4的超导转变温度Tc呈下降趋势。本文采用EHT近似下的紧束缚能带方法,计算了Nb_3X_4的能带结构。讨论其电子结构与超导电性的关系,并从化学键的观点出发对其Tc的递变加以解释。此外,本文还给出了Nb金属晶体的能带结构。     

Si4X(X=C,N,O,Si,P,S)原子簇结构的理论研究

在密度泛函B3LYP/6-311G*水平上, 对具有C3v对称的Si4X (X = C, N, O, P, S)原子簇进行了几何构型优化计算, 并讨论它们的热力学稳定性、动力学活性、Mulliken布居、SiX键长、占据价轨道的对称性以及HOMO能级位置等周期递变规律。     

呋喃同系物C4H4X(X=O,S,Se,Te)三阶非线性光学性质的理论方法比较研究

用ab initio HF，MP2和DFT三种方法的计算结果，根据完全态求和公式自编程序计算了呋喃同系物的三阶非线性光学极化率．结果表明随着杂原子序数的增大，体系的三阶非线性极化率也随着增大，从对称性出发，利用二态模型讨论了体系光学非线性增大的原因．     

C36X(X=O,NH,S)各种可能异构体的芳香性研究

采用拓扑共振能方法对富勒烯C36X(X=O,NH,S)开环结构中的所有可能的异构体及阳离子和阴离子芳香性进行了理论研究. 计算结果表明,C36X的芳香性高于C36. C36X的阳离子因其共振能为负值而具有反芳香性. 反之,C36X的阴离子因共振能为正值而具有芳香性和较高的稳定性. C36的D6h和D2d异构体中杂原子X插入在5-5键时得到的化合物最稳定. 从理论上预测了C36X的负离子能形成稳定的金属富勒烯. 对C36X的阳离子和阴离子的芳香性进行了解释.     

HNCX→HXCN(X=O, S, Se)反应的量子拓扑研究

The reactions of HNCO to HOCN, HNCS to HSCN and HNCSe to HSeCN have been studied at MP2/6-311 ＋ ＋ G（2df, pd）//B3LYP/6-311 ＋ ＋G（2df, pd） level. Geometries of the reactants, transition states and products have been optimized and geometries of the transition states are reported for the first time. The reasons why HNCO and HNCS instead of HOCN and HSCN were easily detected have been explained. It was predicted that HNCSe will be more easily detected than HSeCN. The breakage and formation of the chemical bonds in the reactions have been discussed by the topological analysis method of electronic density. The calculated results show that there are two kinds of structure transition states （STS） in reactions studied.     

Analytic energy derivatives for the equation-of-motion coupled-cluster method: Algebraic expressions,implementation and application to theS 1 state of HFCO

Summary The general theory of analytic derivatives for the equation-of-motion coupled cluster (EOM-CC) method is reviewed. Special attention is paid to the EOM-CC singles and doubles (EOM-CCSD) approximation, which has the same computational scaling properties as the coupled-cluster singles doubles (CCSD) ground state method and is therefore applicable to a wide range of molecular systems. The detailed spin orbital equations that must be solved in EOM-CCSD gradient calculations are presented for the first time, and some guidelines are discussed regarding their computational implementation. Finally, use of the EOM-CCSD gradient method is illustrated by determining the structure, dipole moment components, harmonic frequencies and infrared intensities of formyl fluoride (HFCO) in its singlet excited (n, *) state.     

Spin-orbit corrections to the indirect nuclear spin-spin coupling constants in XH4 (X = C, Si, Ge, and Sn)

Summary Using the quadratic response function at theab initio SCF level of approximation we have calculated the relativistic corrections from the spin-orbit Hamiltonian,H ^SO, to the indirect nuclear spin-spin coupling constants of XH₄ (X = C, Si, Ge, and Sn). We find that the spin-orbit contributions toJ _X-H are small, amounting only to about 1% forJ _Sn-H. For the geminal H-H coupling constants the relativistic corrections are numerically smaller than forJ _X-H, but in some cases relatively larger compared to the actual magnitude ofJ _H-H. We also investigate the use of an effective one-electron spin-orbit Hamiltonian rather than the fullH ^SO in the calculation of these corrections.     

Theoretical study on structures and stabilities of N4X (X = O,S, Se,Te) series

The stable and transition structures of N₄X (X = O, S, Se, Te) series with singlet state are optimized with the ab initio (MP2) and density functional theory (B3LYP) methods using the 6‐311+G(d) basis set. The ring isomers are found to be the global minima for N₄O, N₄S, N₄Se, and the chain isomer is the minimum for N₄Te. The stabilities are studied by evaluating the dissociation barriers with respect to dissociation. The reactants and products connected by transition structures are determined by applying the intrinsic reaction coordinate (IRC) calculations. The C_2v, C_3v and ring isomers decompose into linear NNX and N₂ molecules, however, the chain isomers decompose into cyclic N₂X and N₂ firstly. A new possible isomerization mechanism between the cyclic and linear structures of N₂X series is studied. The cyclic structures of N₂X convert into linear structures easily with the very low barriers. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Studies on reactions INCX --> IXCN (X = O, S, and Se)

The reactions of INCO to IOCN, INCS to ISCN, and INCSe to ISeCN have been studied at the MP2/6-311++G(2df)//B3LYP/6-311++G(2df) level. Geometries of reactants, transition states, and products have been optimized, and geometries of transition states are reported for the first time. The reasons that INCO, ISCN, and ISeCN are easily detected instead of IOCN, INCS, and INCSe have been explained successfully. The breakage and formation of chemical bonds along the reaction paths have been discussed by the topological analysis method of electronic density. The calculated results show that there are two kinds of structure transition states (STS) in the reactions studied.     

氰基铝(AlCN)及其阴阳离子低能激发态的理论研究

在C2v对称性下,采用全活化空间自洽场(CASSCF)和多组态二级微扰理论(CASPT2)方法研究氰基铝(AlCN)及其阴阳离子的基态和低能激发态.在ANO-L基组水平下,计算了AlCN及其阴阳离子低能电子态的几何,组态及其相互作用系数,谐振频率,绝热激发能,垂直激发能和振子强度.在CASSCF/CASPT2理论水平下,计算得到AlCN的11Π电子态的绝热激发能为352.4kJ·mol-1,与实验值344.0kJ·mol-1符合得很好.另外,预测AlCN的跃迁X1Σ+→21Π发生在673.1kJ·mol-1.激发能和振子强度的计算为研究AlCN的吸收光谱提供理论指导.     

X@(HAlNH)12和X(HAlNH)12 (X＝F－, Cl－, Br－, O2－, S2－, Se2－)复合物的结构和稳定性

用DFT的B3LYP方法在6-31G(d)基组的水平上, 对闭式多面体簇合物(HAlNH)₁₂及其内含式X@(HAlNH)₁₂和外接式X(HAlNH)₁₂ (X＝F^－, Cl^－, Br^－, O^2－, S^2－, Se^2－)复合物的结构进行了构型优化和能量计算, 并讨论了几何构型、自然键轨道(NBO)、振动频率、能量参数及NMR数据与结构的关系, 最后得到复合物结构的稳定性信息, 具有T_h对称性的X@(HAlNH)₁₂ (X＝F^－, Cl^－, Br^－, S^2－, Se^2－)复合物和具有C₃对称性的O^2－@(HAlNH)₁₂复合物为内含式的基态结构, 从能量角度分析, 内含式复合物比外接式复合物的结构稳定.