Configuration interaction methods for improving unrestricted Hartree-Fock spin densities

Limited Configuration Interaction wave functions based on Unrestricted Hartree-Fock natural orbitals are found to be easy to compute and to give much more satisfactory spin densities than are provided by techniques currently in use.     

以杂环为铁磁耦合单元的双中心双自由基高自旋有机分子的理论设计

利用－·N－S－为自旋中心（SC），苯为端基（EG），苯、吡啶、哒嗪、嘧啶 、吡嗪、三嗪为耦合单元（FC），设计三种不同排列方式的新型稳定高自旋分子。 由于自旋密度在杂环（FC）和－·N－S－（SC）组成的体系中自由基双中心的部分 离域，导致－·N-S－自由基的特殊稳定性。三种不同的排列方式中，其三重态的 稳定性随主要SC（－N－）原子间距离的增大而降低。从三个系统八个体系三重态 的稳定性来看，FC上的杂原子位于取代基的间位能提高体系的铁磁耦合作用，而位 于邻位和对位则不利于铁磁耦合作用。     

Treating large intermediate spaces in the CIPSI method through a direct selected CI algorithm

Summary A general direct selected configuration interaction algorithm has been implemented and coupled to the second-order multireference many-body perturbation theory CIPSI algorithm. The new direct selected CI code is highly vectorizable and able to handle any list of determinants selected to describe a given electronic state of any spin multiplicity. In the present work selection of determinants has been carried out through the CIPSI algorithm but this is not a constraint of the direct selected CI code. The largest case treated so far involves a CI expansion containing 215 260 determinants selected from single and double excitations from 371 references. In this case there were 8 active electrons in 28 molecular orbitals for NH₃ in a DZP basis set. The direct selected CI calculation needs only 14 Mb of central storage (for the 215 260 determinants case) and takes 406 seconds per iteration on an IBM 3090/600J with vector facility.     

固相配位化学反应研究——LⅦ.阴离子盐KY(Y=Cl,Br,I,CN,SCN)对[Co(NH3)4CO3]Cl热分解的影响

本文通过气相色谱逸出气体分析(EGA)法,配合红外光谱、X-射线粉末衍射等手段,研究了氢气氛中阴离子盐KY(Y=Cl,Br,I,CN,SCN)对配合物[Co(NH_3)_4CO_3]Cl热分解的影响,用Coats-Redfern方法计算了固相反应放出CO_2的动力学参数,得到的活化能值随外加阴离子的不同而有下列顺序:CN~->Cl~->Br~->Г>SCN~-,反应机理均为成核生长机理(F_1).     

Theoretical Studies on Electronic Spectra and Second-order Nonlinear Optical Properties of Glucosyl Substituted Barbituric Acid Derivatives

AMI semi-empirical method was used to optimize the barbituric acid derivatives substituted with glucosyl B1-5 （series B）, and the thiobarbituric acid derivatives substituted with glucosyl T1-5 （series T）. Based on the optimized structures, INDO/CI method was adopted to calculate the electronic spectra. Meanwhile, the second-order nonlinear optical （NLO） coefficients βμ were calculated with the sum-over-state （SOS） formula. The results show that when the number of glucosyl units was increased, ｜βμ｜ values of the barbituric and thiobarbituric acid derivatives were both enhanced, especially for thiobarbituric acid derivatives. It indicates that non-conjugated substituted group could also improve NLO properties of materials when the number of repeated units was increased. Additionally, the absorption bands appearing in UV area are consistent with the proper change of the number of glucosyl units, and consequently it can be concluded that the high transparencies of all systems were scarcely varied.     

Molekulares SSi(H)CI Matrix-IR-Untersuchungen und ab- initio SCF-Rechnungen

The Molecule S?Si(H)CI. Matrix IR Investigation and Initio SCF Calculation Molecular S?Si(H)CI is formed in an argon matrix after the Photochemically induced reaction of SiS with HCI. From the isotopic splittings (H/D and ³⁵,CI/³⁷CI) of the IR absorptions the C_s-structure of the species with silicon as the central atom can be deduced. By an normal coordinate analysis a value of 4.83 mdyn/Å is obtained for the SiS force constant. These experimental results are confirmed by ab initio SCF calculations of the IR spectrum.     

Full CI benchmark calculations for molecular properties

Full CI calculations of first- and second-order properties are presented to provide benchmark results for comparisons with other methods, such as multireference CI(MRCI). The full CI(FCI) polarizability of F^– is computed using a double zeta plus polarization plus diffuse basis set. These FCI results are compared to those obtained at other levels of theory; the CASSCF/MRCI with Davidson correction results are in excellent agreement with the FCI. Differences between the polarizability results computed as a (numerical) second derivative of the energy or as an induced dipole moment are also discussed. FCI calculations are presented for the dipole moment and polarizability of HF, CH₂ and SiH₂ using a DZP basis set. Again, the CASSCF/MRCI values are in excellent agreement with the FCI results, whereas SDCI values, whether computed as an expectation value or as an energy derivative, are much worse. The results obtained using the CPF approach are in considerably better agreement with the FCI results than SDCI, and are similar in quality to the SDCI energy derivative results with the inclusion of Davidson's correction.     

Symmetry adaptation of configuration basis in MCSCF method

Summary A novel approach of space symmetry adaptation is developed for multiconfigurational (MC) functions in fully optimized reaction space and complete active space SCF calculations. The bonded tableau and two box symmetric tableau are basic representations (rep) of configuration functions; the group symmetric localized orbitals are used as one-electron orbitals. The method is proposed for generating a complete and orthonormal set of MC single excited functions. The redundant variable in MCSCF can be eliminated by symmetry adaptation.     

Ab initio CI study of the nitric oxide dimer (N2O2)

Configuration interaction (CI) studies of the ground and electronically excited states are reported for nitric oxide dimer (N₂O₂) in itscis equilibrium geometry. The lowest triplet state (³ B ₂) is found to lie only 0.43 eV above the ground state (¹ A ₁). The¹ A ₁ ¹ B ₁ transition is shown to be responsible for the rising absorption in the near infrared region observed experimentally. The transition of¹ A ₁¹ A ₂ calculated in the visible spectrum range of 701 nm (1.77 eV) is symmetry forbidden.