Home  About us  Contact
 

X Atoms (x + atom)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Adjusting magnetic moments of Sc13 and Y13 clusters by doping different X atom (X = Na, Mg, Al, Si, P)

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 8 2010
Fu-Yang Tian
Abstract We have investigated the structural and magnetic properties of the doped XM12 and charged M13 (X = Na, Mg, Al, Si, P; M = Sc, Y) clusters using the density-functional theory with spin-polarized generalized gradient approximation. It was found that doped atoms can induce significant change of the magnetic moments of Sc13 and Y13 clusters. The total magnetic moments of the NaM12, MgM12, AlM12, SiM12, and PM12 clusters are regular 5, 6 (12), 7, 8, and 9 ,b, respectively (but 19 ,b for Sc13 and Y13, 12 ,b for Y, 18 ,b for Sc, Sc, and Y). The doped atom substituting the surface atom of the plausible icosahedral configuration is viewed as the ground-state structure of the XM12 (X = Na, P; M = Sc, Y) and MgSc12 clusters. While for XM12 (X = Al, Si; M = Sc, Y) and MgY12 clusters, the doped atom occupying the central position of the icosahedral configuration is viewed as the ground-state structure. The doping and the charging both enhance the stability of the Sc13 and Y13 clusters. These findings should have an important impact on the design of the adjustable magnetic moments systems. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

Calculation of proton affinity using the CR-CCSD[T]/ECP method

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2006
Nelson H. Morgon
Abstract High-level calculations of proton and electron affinities (PA and EA) of CH2X, and CH2CHCHX, (with X = F, Cl, Br, and I) systems were obtained. The methodology employed in the PA and EA calculations is based on CR-CCSD[T]/B1//MP2/B0 and CCSD(T)/B1//MP2/B0 levels, respectively. B0 is a (small) valence basis set developed by Stevens and colleagues (SBKJC), and B1 is a larger basis set, with extra diffuse and polarization functions (B0 + s, p, d, and f functions). This scheme has been tested on systems containing H, C, and X atoms, and is shown to give good results. The differences between calculated results of PA and EA and the experimental values are in the range of 0.2,4.5 kJ · mol,1 and 0.01 to 0.10 eV, respectively. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]

A Theoretical Study on the Mechanism of C2H4 Oxidation over a Neutral V3O8 Cluster

CHEMPHYSCHEM, Issue 8 2010
Yan-Ping Ma Dr.
Abstract Density functional theory (DFT) calculations are used to investigate the reaction mechanism of V3O8+C2H4. The reaction of V3O8 with C2H4 produces V3O7CH2+HCHO or V3O7+CH2OCH2 overall barrierlessly at room temperature, whereas formation of hydrogen-transfer products V3O7+CH3CHO is subject to a tiny overall free energy barrier (0.03 eV), although the formation of the last-named pair of products is thermodynamically more favorable than that of the first two. These DFT results are in agreement with recent experimental observations. The (Ob)2V(OtOt). (b=bridging, t=terminal) moiety containing the oxygen radical in V3O8 is the active site in the reaction with C2H4. Similarities and differences between the reactivities of (Ob)2V(OtOt). in V3O8 and the small VO3 cluster [(Ot)2VOt.] are discussed. Moreover, the effect of the support on the reactivity of the (Ob)2V(OtOt). active site is evaluated by investigating the reactivity of the cluster VX2O8, which is obtained by replacing the V atoms in the (Ob)3VOt support moieties of V3O8 with X atoms (X=P, As, Sb, Nb, Ta, Si, and Ti). Support X atoms with different electronegativities influence the oxidative reactivity of the (Ob)2V(OtOt). active site through changing the net charge of the active site. These theoretical predictions of the mechanism of V3O8+C2H4 and the effect of the support on the active site may be helpful for understanding the reactivity and selectivity of reactive O. species over condensed-phase catalysts. [source]