Theoretical Study on the Activity of a-COOH and b-COOH of N-Phosphoryl Aspartic Acids

The bio-mimic reactions of N-phosphoryl amino acids are very important in the study of many biochemical processes. The difference of reactivity between a-COOH and b-COOH in phosphoryl aspartic acid was studied by theoretical study (Hartree-Fock and Density Functional methods) in this paper. The intermediates II containing five-membered ring were more stable than III with six-membered ring. While for intermediates III, the isomers with six-membered ring in apical-equatorial spanning arrangement were more stable than those with di-equatorial spanning arrangement. At B3LYP/6-31G** level, it was shown that transition states IV and V involving a-COOH or b-COOH group had energy barriers of DE = 58.67 kJmol-1 and 103.94 kJmol-1, respectively. These results were in agreement with the experimental data. So the a-COOH group was involved in form of the intramolecular penta-coordinate phosphoric-carboxylic mixed anhydride intermediates, but not b-COOH group.

Theoretical Study on the Reaction of PCl_3/H_2 on Silicon Substrate Surface

The reaction mechanism of PCl3/H2 on silicon substrate surface （simulated by Si4 cluster） was investigated with Density Functional Theory （DFT） at the B3LYP/6-311G^＊＊ level. On silicon substrate, PCl3 firstly undergoes dissociative adsorption, and then the adsorption product reacts with H2 via a four-step multi-channel mode to give the final product PSi4 cluster. The geometries at each stationary point were fully optimized. The possible transition states were determined by vibrational mode analysis and IRC verification. And finally, the main reaction channel was given.

Structures and Properties of Two Pb^Ⅱ Compounds and Theoretical Study of 2,4-Oxybis（benzoic acid）

Two Pb^Ⅱ coordination polymers [Pb（oba）（2,2′-bipy）]·1.5H2O（1） and [Pb（oba）（phen）]（2）（H2oba = 2,4-oxybis（benzoic acid）, 2,2′-bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline） were synthesized by hydrothermal reactions and characterized by single-crystal X-ray diffraction, thermogravimetric analyses, IR spectroscopy and elemental analysis. Structures of compounds 1 and 2 are similar. Compounds 1 and 2 show 1D wavy chains, which are further connected through aromatic π-π stacking interactions to expand into 2D wavelike networks. The crystal structure of 2,4-oxybis（benzoic acid） ligand（3） was obtained, and its full geometry optimization was carried out by using DFT methods at the B3LYP/6-31G（d） level. The calculated data show that the bond distances and bond angles were very close to the experimental data. The values of the frontier orbital energies indicate that this configuration is stable. Moreover, the solid-state fluorescence properties of 1-3 have also been investigated.

Theoretical Study on the Spectroscopic Parameters and Transition Properties of MgH Radical Including Spin-orbit Coupling

An accurate theoretical study on the MgH radical is reported by adopting the high-level relativistic MRCI＋Q method with a quintuple-zeta quality basis set. The reliable potential energy curves of the five A-S states of MgH are derived. Then the associated spectroscopic parameters are determined and found to be in good accordance with the available experimental results. The permanent dipole moments （PDMs） and the spin-orbit （SO） matrix elements of A-S states are computed. The results show that the abrupt changes of PDMs and SO matrix elements are attributed to the variations of electronic configurations at the avoided crossing point. The SOC effect leads to the five A-S states split into ten Ω states and results in the double potential well of （2）1//2 state. Finally, the transition properties from the （2）1//2, （1）3//2 and （3）1//2 states to the ground state X2∑＋1//2 transitions are obtained, including the transition dipole moments, Franck-Condon factors and radiative lifetimes.

Theoretical Study of Carrier Mobility in Two-Dimensional Tetragonal Carbon Allotrope from Porous Graphene

The carrier mobility of two-dimensional tetragonal carbon allotrope （T-CA） from porous graphene is investigated by first-principles calculations. T-CA can be constructed from divacancy and Stone-Thrower--Wales defects from graphene. T-CA is a direct semiconductor with a band gap of 0.4 eV at F point. T-CA possesses a high carrier mobility of the order of 104 cm2V-ls-1. As our study demonstrates, T-CA has potential applications for next-generation electronic materials.

Theoretical Study on the Pyrolysis Mechanism and Kinetics of 3-Hydroxy-3-Methyl-2-Butanone

The mechanism and kinetics for the decomposition of 3-hydroxy-3-methyl-2-butanone have been studied by using the ab initio RHF/3-21G method. The calculated activation barrier of the reaction is 249.6kJ/mol which is in reasonable agreement with the experimental data (222.2±3kJ/mol). The calculated results show that the decomposition is a concerted process with hydrogen transferring and bond breaking via a five-membered cyclic transition state. The thermal rate constants of the decomposition are obtained by calculating microcanonical probability fluxes through transition state1.

Theoretical Study on the Reaction Mechanism between Dichlorocarbene and Armchair Single-walled Carbon Nanotubes

The reaction mechanism between CC12 and armchair single-walled carbon nanotubes （ASWCNTs） （3,3） and （4,4） has been studied by semiempirical AM1 and ab initio methods. The activation barriers of CC12 adding to ASWCNT （3,3） and （4,4） are computed and compared. The lower barrier of CC12 forms cycloaddition isomer on （3,3） maybe because the strain energy of （3,3） is larger than that of （4,4）. Our theoretical results are consistent with the experimental results.

Theoretical Study on the Gas Phase Reaction of Au^+ with CS_2

The reaction of Au＋（1S,3D） with CS2 has been investigated at the B3LYP and CCSD（T） levels of theory.The identified reaction pathways revealed that the experimentally observed products,AuS＋ and AuCS＋,can be produced by the insertion of Au＋ into C-S bond.The calculated energetics shows that the reactions on singlet surface lead to excited-state products,AuS＋（1Σ） ＋ 1CS and AuCS＋（1Σ） ＋ 1S,and have notable energy barriers,whereas the reactions on triplet surface producing the ground state products of AuS＋（3Σ） ＋ 1CS and AuCS＋（1Σ） ＋ 3S are energetically much more favorable.This result suggests that the minor formations of AuS＋ and AuCS＋ observed in the previous experiment under room-temperature condition should result from the reactions of excited-state Au＋（3D） with CS2.Further,the possibility for singlet-triplet surface crossing was also discussed by approximately determining the crossing region.

Theoretical Study on the Structures, Vibrational Spectra, and the Nature of the Intermediate Hydrogen Bond of Schiff Bases

Semi-empirical method PM3 was used to study the geometry and vibrational spectrum of N-(2-hydroxy-l-naphthyl-methylene)-l-pyrenamine (NPY) with the intermediate hydrogen bond. Results are comparable to experimentations. Based on results of both NPY and its model, N-(2-hydroxy-l-naphthyl-methylene)aniline, it was found that the N-(2-hydroxy-l-naphthyl-methylene) group is principally responsible for the special hydrogen bonding through conjugation effect.

A THEORETICAL STUDY OF THE THERMODYNAMIC AND KINETIC PROPERTIES FOR THE REACTION OF FORMYL CYANIDE DECOMPOSITION

We compute the thermodynamic and the kinetic properties for the reaction: HCOCN→HCH+CO using the statistical theory and the transition-state theory.The equi- librium constants and the rate coefficients of this reaction are also reported here,and the half lives of formyl cyanide at different temperatures are first estimated in this work.

THEORETICAL STUDY ON THE EXCITED STATES AND STABILITIES OF B_3, B_3^- AND B_3^+

The geometries and vibrational frequencies of the ground and low-lying excited states for B_3, B_3^- and B_3^+ are determined with the energy gradient method using the polarized double-zeta(6-31G*) basis set. The stabilities for the states of B_3,B_3^- and B_3^+ have been investigated based on the vibrational analysis. The correlation energy obtained for each state is considered with the configuration interaction (CISD+Q) technique. B_3 and B_3^+ have stable equilateral triangle geometry, while B_3^- has stable equilateral triangle, isosceles triangle and linear geometries. The Jahn-Teller distortion for a ~3E' state of B_3^- in D_(3h) symmetry is also discussed.

Theoretical Study of Small Water Clusters of Sulfur Dioxide

The intermolecular clusters of sulfur dioxide with water, SO2（H2O）n （n = 2～5）, are studied by using B3LYP density functional theory and MP2 ab initio methods along with the large basis sets （6-311＋＋G（d,p） and aug-cc-pVDZ）. The equilibrium geometries, intermolecular binding energies, and anharmonic frequencies of the clusters are calculated and compared with those of pure water clusters and available experiments. SO2 tends to form cyclic hydrogen-bonded complexes with two or three water molecules. In the larger clusters, however, water molecules begin to retain the structure of pure water clusters and segregate from SO2. Infrared absorption assignments for the small clusters are discussed to resolve a possible incorrect assignment in a recent spectroscopic experiment on the clusters.

Theoretical Study on the Charge Transport Properties of Coronene and Its Derivatives

Molecular structures, reorganization energies and charge transport matrix elements of coronene and its fluoro-, hydroxyl- and sulfhydryl-substituted derivatives have been studied at the B3LYP/6-31G＊＊ level. Based on the semi-classical model of electron transfer, charge transport rate constants of the title molecules have been calculated. The results indicate that the coronene molecule is helpful to the transport of negative charge, and the transport rate of positive charge is between those of hexaazatriphenylene and triphenylene.

Theoretical Study on the Structure and Stability of Si_5X (X = Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl) Clusters

Density functional theory B3LYP/6-311 G＊ method was used in the geometry optimization and frequency calculation on Si5X （X = Li, Be, B, C, N, O, E Na, Mg, Al, Si, P, S, Cl） clusters. The influence of the doped second and third period element impurities on the structure and stability of Si5X clusters with C2p symmetry has been investigated, and the thermal stability and dynamic activity have also been discussed.

THEORETICAL STUDY ON THE CONFIGURATION OF [PdCl_2(C_2H_4OH)]-

The configuration of[PdCl_2(C_2H_4OH)]^- has been studied by pseudopotential ab initio method.A cis isomer was found to be the reaction intermediate in the Wacker process.

Theoretical Study on the Structure and Stability of Si_4X (X = Li, Be, B, C, N, O, F) Clusters

The density functional theory B3LYP/6-311g* method is used in the geometry optimization and frequency calculation on Si4X (X = Li, Be, B, C, N, O, F) clusters. The equi- librium structures of these clusters are quasi-trigonal bipyramidal structures with C2v symmetry. The periodicity of their thermal stabilities and vibration spectra has been discussed. The influence of the inserted second period element impurities for the structures and stabilities of the Si5 clusters have also been investigated.

THE THEORETICAL STUDY ON INTERSECTION POINT RULE FOR HOMOLOGUES IN GAS CHROMATOGRAPHY

The intersection point rule for homologues in gas chromatography was discovered many years ago,now more and more application and development are occurring in recent years~[2-6], but there are few systemic theoretical studies.In this paper,based on the basic equation of reten- tion values in gas chromatography,we prove the intersection point rule of homologues from mathematics,study the factors affecting intersection point position,give the physical meaning of intersection point,and explain the experimental rules in references.

Theoretical Study of Screening Dependence of Aluminium Doped MgB_2

The screening dependence of superconducting state parameters （λ, μ＊, Tc, α and NoV） of six alloys of aluminium doped MgB2 systems are studied in the BCS-Eliashberg-MeMillan framework by employing five forms of dielectric screening function, viz. random phase approximation （RPA）, Harrison, Geldart and Vosko （GV）, Hubbard and Overhauser in conjunction with Ashcroft＇s potential. It is observed that electron-phonon coupling strength and Coulomb pseudopotential μ＊ are quite sensitive to the form of dielectric screening, whereas transition temperature Tc, isotope effect exponent α and effective interaction strength NoV show weak dependence on the form of dielectric screening function. It is found that the RPA form of dielectric screening function yields the best results for transition temperature Tc for all alloys of the Mg-Al-B system. The results obtained using GV screening are much higher than the experimental results. This shows that all the four dielectric screenings used here almost describe superconductivity in all the alloys of the Mg-Al-B system, but the GV screening is not suitable for such an alloy system.

THEORETICAL STUDY ON PHOTODECARBONYLATION REACTION OF ACROLEIN

Photodecarbonylation reaction of acrolein at 193nm was investigated by ab initio molecular orbital method.Our result supports photodecarbonylation mechanisms proposed by Fujimoto,and predicts that the reaction should occur in ~3ππ potential energy surface prior to the ~1ππ potential energy surface.

AB INTIO THEORETICAL STUDY OF MIXED CLUSTER AICB

By uae of ab initio and analytic energy gradient method, twelve optimized electronic states of AICB,AIBC, BAIC in six geometric configurations are determined at all electron UHF(RHF) /6-31G level, their singles and doubles CI (CISD) energies are also obtained. The Stabillties for the atates of AICB have been investigated based on the vibrational analysis. binding energy and fragmentation energy. The ground state is 3∑+ of AICB (C∞. TAIC= 1.7497.,TBC=1.3511 A = 206.7, 799.5, 1802.9 cm-1, T=0), the second state is 1A' of AICB (Cs,TAIC=1.9162, TBC = 1.3154 A, ∠AICB=179。8307, =238.5, 575. 1,1767. 5.cm-1, T =2432.84 cm-1). The fragmentations of vallous States (fragmentation products are AIB,AIC, BC diatomic clusters. and Al, B, C free atoms) of AIBC, AICB. BAIC are discussed in detail.