Qiugen Zhang

A theoretical study for the isomers of neutral, cationic and anionic phosphorus clusters P5, P7, P9

Abstract The cations and anions of P 5 , P 7 and P 9 exhibit intensities of significance on the mass spectra of phosphorus clusters produced in direct laser vaporization. We have acquired in the total fifty isomers of P 5 , P 7 , P 9 and their cations and anions by means of the B3LYP, DFT method. According to total energies, the most stable isomers have been predicted. A cationic cluster prefers to adopt structures with an atom(s) which is four-fold coordinated. The planar pentagon structure is a frequent sub-unit in the phosphorus clusters. Both tetrahedral P 4 and cuneane P 8 are common components of the clusters and can be considered as important units for the construction of large clusters.

A Fully Flexible Potential Model for Carbon Dioxide

National Natural Science Foundation of China [50573063]; Program for New Century Excellent Talents in University of the State Ministry of Education [NCET-05-0566]; Specialized Research Fund for the Doctoral Program of Higher Education of China [2005038401]

A density functional study for the isomers of anionic sulfur clusters S-n(-) (n=3-20)

Abstract The signals of anionic sulfur clusters are intense in the mass spectrum of sulfur clusters generated in direct laser vaporization. We have acquired numerous isomers of sulfur clusters by means of the B3LYP DFT method. According to total energies, the most stable Sn− (n=3–13) isomers are predicted. The helical Sn (n=14–20) structures are also calculated. Most of the anionic clusters are with chain configurations; the ring clusters with threefold atom(s) are higher in total energy. The most stable forms of isomers, from S9− to S13−, show helical configurations that are completely different from those of the corresponding neutral and cationic clusters.

Geometric structures and structural stabilities of neutral sulfur clusters

Abstract We have acquired a total of 68 isomers of sulfur clusters S n ( n =3–11) based on molecular graphics and then carried out optimizations and vibrational analysis by means of the B3LYP DFT method. Inside these structures, the sulfur atoms could be in one-fold, two-fold and/or three-fold coordination. According to total energies, the isomers have been ranked for stability. Many sulfur clusters are composed of atoms in two-fold mode. Compared to a S n structure with all atoms in two-fold mode, that with atom(s) in one-fold and three-fold coordinations is higher in energy. It seems that it is difficult for a sulfur cluster to form a cage structure with the involvement of three-fold atom(s)

Metal in situ surface functionalization of polymer-grafted-carbon nanotube composite membranes for fast efficient nanofiltration

The development of inorganic functionalized membranes with the capacity to effectively separate molecules or ions in solutions based on the size or electrostatic interactions is pivotal to purification and separation applications. Herein, we demonstrate a novel green strategy utilizing a completely aqueous process to construct an asymmetrically structured metal surface functionalized polymer–matrix nanocomposite nanofiltration membrane. Crosslinked polyethyleneimine (PEI) is grafted on a carboxylated carbon nanotube intermediate layer incorporated into the macroporous cellulose acetate substrate to form the composite membrane. The resulting membrane is subsequently inorganically modified via an in situ surface reaction of zinc nitrate with excess ammonium hydroxide to produce the hydrophilic and positively charged membrane. Crosslinking enhances the polymer interaction with the carbon nanotube interlayer which in turn endows it with mechanical strength and sustains the membrane pore structure during pressure driven filtration. The functionalized membrane displays outstanding pure water flux of 16.5 ± 1.3 L m−2 h−1 bar−1 while exhibiting good nanofiltration performance of bivalent cations, which is ascribed to the electrostatic repulsion via the Donnan exclusion effect. Meanwhile the membranes exhibit excellent separation of organic molecules and long-term filtration stability. This newly developed approach presents a promising route for the construction of highly permeable nanofiltration membranes for fast purification and separation applications.

Density Functional Theory Study of CsCn− (n = 1−10) Clusters

In this paper, we report the design of numerous models of CsC(n)(-) (n = 1-10). By means of B3LYP density functional method, we carried out geometry optimization and calculation on the vibrational frequency. We found that the CsC(n)(-) (n = 4-10) clusters with Cs lightly embraced by C(n) are ground-state isomers. The structures are composed of C(n)(2-) and Cs(+) with the former being electronically stabilized by the latter. When n is even, the C(n) (n = 4-10) chain is polyacetylene-like. The CsC(n)(-) (n = 1-10) with even n are found to be more stable than those with odd n, and the result is in accord with the relative intensities of CsC(n)(-) (n = 1-10) observed in mass spectrometric studies. In this paper, we provide explanations for such trend of even/odd alternation based on concepts of the highest vibrational frequency, incremental binding energy, electron affinity, and dissociation channels.

Theoretical study of low-lying electronic states of CuO and CuO−

Abstract Abstract: DFT (B3LYP) calculations on the spectroscopic properties of the low-lying states of CuO and CuO − have been carried out. The corresponding electronic spectrum has been estimated by using MRSDCI, MP4(SDQ) and CCSD(T) methods. The results support the assignment, based on the recent photoelectron spectroscopic (PES) experiment that the state at 1.91 eV is a CuO( 4 Σ − ) and the CuO( 2 Δ ) arising from the electron detachment of a 3d electron of CuO − is more than 2.2 eV above the ground state of CuO(X 2 Π ). Our calculations suggest that the feature a′ in the PES experiment of CuO − should be due to the 1 1 Π excited state, rather than due to the spin-orbit splitting component of the 1 3 Π state as suggested in the PES experiment.

Theoretical study of the insertion reactions of Zr+ into HF, HCl, H2O, H2S, NH3, PH3, CH4, and SiH4

The insertion reactions of transition metal cation doublet Zr + ( 2 D) into HF, HCl, H 2 O, H 2 S, NH 3 , PH 3 , CH4, and SiH 4 have been studied by means of ab initio molecular orbital calculations incorporating electron correlation with the Moller-Plesset perturbation theory up to the second and the fourth orders and the hybrid density functional method, B3LYP. Three regions of the potential surface have been investigated, an ion-molecule complex, followed by a three-center, four-electron transition state, and then an insertion product. It is found that all insertion reactions are exothermic and all transition states are below the energy surfaces of the reactants. For the ion-molecule complexes, the binding energies of the same-row hydrides increase from right to left, with the exception of CH 4 and SiH 4 , whose binding energies decline considerably; while to the same-group hydrides the ion-molecule complexes in the up row are more bound than those in the down row. The stability of the insertion product H-Zr + -RH n - 1 decreases from right to left across the row and falls from up to down across the column. The reaction barrier follows the same trend; i.e., the more exothermic the insertion reaction is, the lower is the reaction barrier. All these observed trends could be understood by a combined effect of the electrostatic interaction and the covalent interaction.

A density functional study for the isomers of cationic sulfur clusters

Abstract The cations of sulfur clusters exhibit intensities of significance on the mass spectra of sulfur clusters generated in direct laser vaporization. We have acquired numerous isomers of cationic sulfur clusters by means of the B3LYP DFT method. According to total energies, the most stable S n + ( n =3–13) isomers are predicted. Many cationic clusters are composed of two-fold atoms; those with one-fold and three-fold atoms are higher in total energy. The most stable isomer of some cationic clusters shows a structure completely different from that of the corresponding neutral cluster.

The hybrid DFT and molecular orbital study of structure and molecular bonding of FeO4 and FeO4

Abstract The structures, vibrational frequencies and molecular bonding of FeO 4 and FeO 4 − species with different spin states have been investigated by the hybrid DFT, ab initio Hartree–Fock and post-Hartree–Fock molecular orbital methodologies. For FeO 4 − , the properties of the ground state strongly depend on the level of the calculation. The quasi-tetrahedron FeO 4 − ( 2 B 1 ) was predicted to be the lowest by DFT and MP4(SDQ) calculations, while the doublet (O 2 )FeO 4 − ( 2 A 2 ) was found to be the lowest at CISD/B3P86 and CCSD/B3P86 levels. The ground state of neutral FeO 4 species is the singlet (O 2 )FeO 2 ( 1 A 1 ) at B3P86 and CISD/B3P86 levels of theory. Most of the strong bands for the isomers of FeO 4 and FeO 4 − appear at about 1000xa0cm −1 . The molecular bondings in FeO 4 and FeO 4 − species containing cyclic Fe(O 2 ) subunits, bring about a net charge transfer from Fe and the bonding π orbital into anti-bonding π orbital of O 2 , which activate the O–O bond in coordinated O 2 . Larger O–O bond lengths in the cyclic Fe(O 2 ) subunits than in the isolated O 2 and O 2 − were observed.