C. C. Sun

THEORETICAL STUDY ON POTENTIAL-ENERGY SURFACE OF C2N2

B3LYP and CCSD(T) (single-point) calculations are performed on structures and interconversion transition states for five C2N2 isomers, i.e., the linear structures NCCN 1, CNCN 2, CNNC 3, and CCNN 4, and the NNC three-membered ring structure with exocyclic C–C bonding 5. A schematic potential-energy surface of the five C2N2 isomers is established. It is shown that the elusive and long searched for isomer 3 lies in a deep potential well against isomerization to the well-studied isomers 1 and 2, while the two transition states, which have been predicted to connect the isomers 1 and 3, are actually associated with the interexchange of the two cyano groups in isomer 2. It is also shown that the experimentally unknown but expectedly important isomer 4 may take an isomerization pathway to the isomer 1 via the intermediate 5, and the isomer 4 also lies in a deep potential well. Both the isomers 3 and 4 may be thermally as stable as the isomer 2. The results presented in this paper may provide useful information f...

COMPARATIVE STUDY OF THE SECOND-ORDER OPTICAL PROPERTIES OF SPIROCONJUGATED COMPOUNDS VERSUS THE CORRESPONDING POLYENES AND POLYPHENYLENES

Abstract Using the AM1 and INDO/CI methods, we studied the structures and electronic spectra of spiroconjugated compounds Download : Download full-size image (n=1–5) (I). On the basis of the results obtained, according to the sum-over-states formula, the calculation program was devised and the nonlinear second-order optical susceptibilities were calculated. The results were compared with the results of corresponding polyenes- and polyphenylenes-linked compounds (II) and (III) that were calculated using the same methods. It is concluded that although the nonlinear second-order optical susceptibilities βμ of spiroconjugated compounds (I) are less than that of (II) and (III), but the transparency is better than that of (II) and (III). When the number of 1,4-cyclohexadiene rings increase, i.e. as the spiroconjugation path lengthens, the βμ values increase without a significant increase of λmax. Thus, we conclude that the spiroconjugated compound (I) will be a hopeful second-order nonlinear optical material from the standpoint of its high transparency and the relatively medium β value.

On the magnetic properties of compounds Y1−xNdxCo5

Abstract By considering the exchange interaction, the crystal field interaction and the spin-spin dipole interaction in the Hamiltonian, some magnetic quantities of the compounds Y 1− x Nd x Co 5 such as magnetization, etc., are studied by the conventional parameter-fitting method. It is shown that the calculated results are in agreement with the magnetic experiments and the improper temperature-dependent behaviour of the second-order crystal field parameter calculated by the previous investigators is improved.

An ab initio study on silicon-doped carbon clusters

Abstract The possible structures of C n Si ( n =28,29,49,50) are calculated by using the Hartree–Fock method. Our studies show that C 29 Si and C 49 Si are networked closed-cages where the silicon atom just replaces a suitable site of C 30 and C 50 fullerenes, thus the most stable structures of C 29 Si and C 49 Si come from those of C 30 and C 50 , respectively. The binding energy suggests that C 29 Si and C 49 Si have lower stability than the C 30 and C 50 , respectively, and the silicon atom is an active site. For the two kind of structures of C 28 Si and C 50 Si, namely, (I) exohedral and (II) hole-defect (the silicon atom connects to four carbon atoms), the exohedral complexes are more stable and would be the main ingredient in the laser vaporation of the silicon-graphite target.

Curing Theory and Scaling Study: Crosslinking Reaction of the Aa Type

Abstract The process of the Aa-crosslinking reaction is considered as a whole to approach the threshold of the sol-gel transition. By a rational way, without Stirlings approximation, the asymptopic form of the Flory-Stockmayer distribution near the gel point is obtained to reach a generalized scaling law.

Symplectic symmetry of Hubbard model and η pairing

By means of symplectic group Sp(2M), the symplectic symmetry of the Hubbard model and the η pairing are investigated to approach the eigenstates which have the largest spin multiplicities. The behavior of the off‐diagonal long‐range order of these eigenstates is examined by the criterion proposed by Yang and the energy diagram of the corresponding eigenvalues is elucidated by the η pairing mechanism. A basis set which is expressible in terms of η and ηa pairings is proposed.

A four-component model for volume phase transition

Abstract By means of the Flory-Huggins and Iwatsubo theory for macromolecules, a four-component model of a hydrogel, which consists of a copolymer network and a solution with two solvents, is given for discussing the “normal pattern” volume phase transition which was proposed by Katayama. Furthermore, the theoretical result shows that an ionic gel can also undergo a volume phase transition caused by the variation of the ratio of the two components in the copolymer network.

Analysis of the magnetic properties of Pr2Co17 and Nd2Co17

Abstract By means of an improved Hamiltonian, in which the spin-spin dipole interaction is included, some magnetic quantities of the compounds Pr 2 Co 17 and Nd 2 Co 17 , such as the magnetization, cone angle, etc., have been studied by the conventional parameter-fitting method. It is shown that the calculated results are in agreement with the experimental magnetic data. In particular, the accommodation of the measurements without the spin-spin dipole interaction leads to different values of the second-order crystal field parameter A 2 staggered 0 at different temperatures, a physically undesirable circumstance, and to significant deviations of the calculated cone angles from experiments. These inadequate calculated results of A 2 staggered 0 and θ c ( T ) are improved in this paper.

Crosslinking reaction of type Aa involving intramolecular cyclization

Abstract An alternative way is proposed to approach crosslinking reactions of Type A a by taking into consideration intramolecular cyclization. The sol fraction for postgelation is investigated to deduce the equilibrium number distribution of n-mer, with the Flory-Stockmayer distribution as a criterion. Furthermore, scaling study leads directly to a generalized scaling law.

THE PARAMETER-DEPENDENT FERMION STATES FOR MOLECULES WITH SYMPLECTIC SYMMETRY

Under a certain kind of similarity transformation, a parameter-dependent (abbreviated as PD) symplectic group chain Sp(2M) ⊃ Sp(2M - 2) ⊃ ⋯ ⊃ Sp(2) that is characterized by a set of pairing parameters is introduced to build up the PD antisymmetrized fermion states for molecules with symplectic symmetry, and these states will be useful in carrying out the optimization procedure in quantum chemistry. In order to make a complete classification of the states, a generalized branching rule associated with the symplectic group chain is proposed. Further, we are led to the result that the explicit form of the PD antisymmetrized fermion states is obtained in terms of M one-particle operators and M geminal operators.