Search

The potential energy landscape of the neutral Ni2(CO)5 complex was re-examined. A new C2v structure with double bridging carbonyls is found to compete with the previously proposed triply carbonyl-bridged D3h isomer for the global minimum of Ni2(CO)5. Despite that the tri-bridged isomer possesses the more favored (18, 18) configuration, where both metal centers satisfy the 18-electron rule, the neutral Ni2(CO)5 complex prefers the di-bridged geometry with (18, 16) configuration. The isomerization energy decomposition analysis reveals that the structural preference is a consequence of the maximization of electrostatic and orbital interactions. [ABSTRACT FROM AUTHOR]

Based on the combination of novel carbon material graphynes (GYs) and superalkalis (OM3), a class of GY superalkali complexes, OM3+@(GY/GDY/GTY)− (M = Li, Na, and K), has been designed and investigated using the density functional theory method. Computational results reveal that these complexes with high stability can be regarded as novel superalkali salts of GYs due to electron transfer from OM3 to GYs. For second‐order nonlinear optical response, these superalkali salts exhibit large first hyperpolarizabilities (β0). Two essential effects on β0 values are found, namely, the atomic number of alkali atom in superalkali and the pore size of GY. Integrating the two effects, the selected combination of OLi3 with large pore size graphtrigne (GTY) can lead to a considerable β0 value (6.5 × 105 au), which is a new record for superatom‐doped GYs. In the resulting complex, the OLi3 unit is located at the center of the pore of GTY, forming a planar structure with the highest stability among these salts. Besides large β0 values, these superalkali salts of GYs have a deep‐ultraviolet working region; hence, they can be considered a kind of high‐performance deep‐ultraviolet NLO molecule. [ABSTRACT FROM AUTHOR]

The average magnetic moment per atom of Mn13 cluster is expected to be enhanced by doping or coating with a shell. Several ternary core–shell icosahedral clusters TM@Mn12@Au20 were constructed by combining substituting the central Mn with VIII elements (Fe, Co, Ni, Ru, Rh, Pd and Pt) and coating with a icosahedral Au20 shell, and systematically studied by using the first-principles density functional method. Compared to Mn13, Fe@Mn12@Au20 cluster shows a giant enhancement on total magnetic moment (52 µB) which can be greatly attributed to the ferromagnetic coupling between spin moments of atoms. Coating with Au20 shell enlarged the average distances of TM-Mn and Mn-Mn and is a useful way to change the magnetic coupling style. By analysis of density of states and electron localisation functional, we can conclude that the weak hybridisation between Fe and Mn in Fe@Mn12@Au20 is propitious to maintain their original direction of spin moments of atoms and then form ferromagnetic coupling. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemical approach based on protein controllable unfolding was developed and applied in combination with in-situ reaction in order to investigate the electrocatalytic pathway for hemoglobin (Hb) toward nitric oxide (NO). Hb was entrapped in a dimethyldidodecylammonium bromide (DDAB) film modified glassy carbon electrode (DDAB/Hb/GCE). Two typical denaturants of acid and urea were synergistically utilized to control the incorporated Hb to a most unfolded state without losing heme groups. Under optimal conditions, the unfolded DDAB/Hb/GCE exhibited accelerated direct electron transfer. The sensitivities for the detection of ascorbic acid (AA), NaNO2 and NO were improved as 3, 10 and 12 times higher than those on the native DDAB/Hb/GCE, and the limits of detection (LODs) for AA, NaNO2 and NO were down to 0.33, 0.83 and 0.063μM, respectively. The unfolded DDAB/Hb/GCE was further applied for the investigation of Hb–NO interaction in NaNO2 solution. With successive additions of AA, NO was generated in situ on DDAB/Hb/GCE. A new reduction peak of the intermediate HbFe(II)–HN2O2 was successfully revealed near −0.65V. The whole electrocatalytic mechanism was proposed and verified by density functional theory. The method can be a promising platform for facile study of the interaction between NO and heme proteins. [Copyright &y& Elsevier]

Based on DFT-B3LYP/6-311G** method, the molecular geometric structures of polynitramineprismanes are fully optimized. The detonation performances, energy gaps, strain energies, as well as their stability were investigated to look for high energy density compounds (HEDCs). Our results show that all polynitramineprismanes have high and positive heat of formation. To construct the relationship between stabilities and structures, energy gaps and bond dissociation energies are calculated, and these results show that the energy gaps of prismane derivatives are much higher than that of TATB (0.1630). In addition, the C-C bonds on cage are confirmed as trigger bond in explosive reaction. All polynitramineprismanes have large strain energies, and the strain energies of all compounds are slightly smaller than prismane, which indicated that the strain energies were somewhat released compared to prismane. Considering the quantitative criteria of HEDCs, hexanitramineprismane is a good candidate of high energy compounds. [ABSTRACT FROM AUTHOR]

Iridium (III) 2-phenylpyridine (ppy) complexes with two suitable monodentate L ligands [Ir(ppy)(L)] (ppy = 2-phenylpyridine, py = pyridine, L = 4-pyCN 1, 4-pyCHO 2, 4-pyCl 3, py 4, 4-pyNH 5) were studied by density functional theory (DFT) and time-dependent DFT methods. The influences of ligands L on the electronic structure and photophysical properties were investigated in detail. The compositions and energy levels of the lowest unoccupied molecular orbital (LUMO) are changed more significantly than those of the highest occupied molecular (HOMO) by tuning L ligands. With the electronegativity decrease of L ligands 4-pyCN > 4-pyCHO > 4-pyCl > py > 4-pyNH, the LUMO distributing changes from py to ppy, and the absorptions have an obvious red shift. The calculated results showed that the transition character of the absorption and emission can be changed by adjusting the electronegativity of the L ligands. In addition, no solvent effect was observed in the absorptions and emissions. [ABSTRACT FROM AUTHOR]

The derivatives of purine are designed through substituting the hydrogen atoms on it for nitro and amino functional groups. Geometries and frequency are analyzed at the B3LYP/6-31 G** level of density functional theory (DFT). Heats of formation (HOF), bond dissociation energy (BDE) and detonation parameters (detonation velocity and detonation pressure) are obtained in detail at the same level. It is found that the BDE values of all derivatives are over 120KJ·mol, and have high positive heats of formation. These derivatives possess excellent detonation properties, for B1, B2, and C, the detonation velocity are 9.58, 9.57, and 9.90 km·s, and the detonation pressure are 43.40, 46.05, and 46.37 Gpa, respectively, the detonation performances are better than cyclotrimethylenetrinitramine (RDX) and cyclotetramethylenetetranitramine (HMX). Hence, the derivations of purine may be promising well-behaved high energy density materials. [ABSTRACT FROM AUTHOR]

A series of polynitroprismanes, CH(NO) ( n = 1-6) intended for use as high energy density compounds (HEDCs) were designed computationally. Their electronic structures, heats of formation, interactions between nitro groups, specific enthalpies of combustion, bond dissociation energies, and explosive performances (detonation velocities and detonation pressures) were calculated using density functional theory (DFT) with the 6-311 G** basis set. The results showed that all of the polynitroprismanes had high positive heats of formation that increased with the number of substitutions for the prismane derivatives, while the specific enthalpy of combustion decreased as the number of nitro groups increased. In addition, the range of enthalpy of combustion reducing is getting smaller. Interactions between ortho (vicinal) groups deviate from the group additivity rule and decrease as the number of nitro groups increases. In terms of thermodynamic stability, all of the polynitroprismanes had higher bond dissociation energies (BDEs) than RDX and HMX. Detonation velocities and detonation pressures were estimated using modified Kamlet-Jacobs equations based on the heat of detonation ( Q) and the theoretical density of the molecule ( ρ). It was found that ρ, D, and P are strongly linearly related to the number of nitro groups. Taking both their energetic properties and thermal stabilities into account, pentanitroprismane and hexanitroprismane are potential candidate HEDCs. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of chemical fixation of carbon dioxide with 2-aminobenzonitrile catalyzed by 1-butyl-3-methyl imidazolium hydroxide ([Bmim]OH) ionic liquid has been extensively investigated by the density functional theory (DFT) calculations. The purpose is to show the detailed reaction mechanism, and in particular to better understand the role of [Bmim]OH played in the reaction as a catalyst. Three mechanistic pathways are proposed and evaluated. Our calculations indicate that the real activate catalyst is the N-heterocyclic carbine (NHC). In the favored pathway, it is found that the attack of C3 atom of NHC to C1 atom, the C1–O2 bond cleavage, and the C1–N2 bond formation have close activation free energies. Therefore, each of them can determine the reaction rate with variation in the reaction conditions. Furthermore, it is shown that the scCO2 solution does not change significantly the potential energy surface profile. [Copyright &y& Elsevier]

A theoretical study of L-proline- nHO ( n = 1-3) has been performed using the hybrid DFT-B3LYP and MP2 methods together with the 6-311++G(d,p) basis set. The results show that the P2 conformer is energetically favorable when forming a hydrated structure, and the hydration of the carboxyl group leads to the greatest stability. For hydrated complexes, the adiabatic and vertical singlet-triplet excitation energies tend to decrease with the addition of water molecules. The hydration energy indicates that in the hydrated complexes the order of stability is: binding site 2 > binding site 1 > binding site 3, and binding site 12 > binding site 23 > binding site 13. As water molecules are added, the stabilities of these hydrated structures gradually increase. In addition, an infrared frequency analysis indicated that there are some differences in the low-frequency range, which are mainly dominated by the O-H stretching or bending vibrations of different water molecules. All of these results should aid our understanding of molecular behavior and provide reference data for further studies of biological systems. [ABSTRACT FROM AUTHOR]

The non-classical KP6Mo18O73heteropolyanion has been studied by the density functional theory (DFT) method, and the calculated geometry compares well with the experimental one. In fully oxidized [KP6Mo18O73]7−state, the dxy-orbitals centered at eight “belt” Mo sites in the lower part of the “basket” are the major contributors to the LUMO and LUMO+1, while the LUMO+2 orbital is mostly focused on the two polar parts. In contrast, the HOMOs indicates that the coordination of the KP6Mo18heteropolyanion to metal ions favorably occurs at the oxygen atoms from four external phosphates and two molybdates of the handle of the “basket”. Compared with Wells–Dawson [P2Mo18O62]6−, the HOMO–LUMO gap in fully oxidized [KP6Mo18O73]7−is much smaller, indicating much easier reduction that is consistent with the cyclic voltammogram. Both frontier orbitals and Mulliken analysis indicate that two of three blue electrons in [KP6Mo18O73]10−(KP6Mo18-3e) have spin alpha while third blue electron has spin beta, in agreement with magnetic data. The four-copper complex of the non-classical KP6Mo18-3e heteropolyanion has been synthesized and structurally characterized; its structure supports the theoretical results such as reactivity and basicity of external oxygen sites. [ABSTRACT FROM AUTHOR]

The non-classical KP6Mo18O73heteropolyanion has been studied by the density functional theory (DFT) method, and the calculated geometry compares well with the experimental one. In fully oxidized [KP6Mo18O73]7−state, the dxy-orbitals centered at eight “belt” Mo sites in the lower part of the “basket” are the major contributors to the LUMO and LUMO+1, while the LUMO+2 orbital is mostly focused on the two polar parts. In contrast, the HOMOs indicates that the coordination of the KP6Mo18heteropolyanion to metal ions favorably occurs at the oxygen atoms from four external phosphates and two molybdates of the handle of the “basket”. Compared with Wells–Dawson [P2Mo18O62]6−, the HOMO–LUMO gap in fully oxidized [KP6Mo18O73]7−is much smaller, indicating much easier reduction that is consistent with the cyclic voltammogram. Both frontier orbitals and Mulliken analysis indicate that two of three blue electrons in [KP6Mo18O73]10−(KP6Mo18-3e) have spin alpha while third blue electron has spin beta, in agreement with magnetic data. The four-copper complex of the non-classical KP6Mo18-3e heteropolyanion has been synthesized and structurally characterized; its structure supports the theoretical results such as reactivity and basicity of external oxygen sites. [ABSTRACT FROM AUTHOR]

Using density-functional calculations within the generalized gradient approximation (GGA)+U framework, we investigate the structural, electronic, and magnetic properties of the ground states of SrFeOn (n = 2 and 2.5). The magnetism calculations show that the ground states of both SrFeO2 and SrFeO2.5 have G type antiferromagnetic ordering, with indirect band gaps of 0.89 and 0.79 eV, respectively. The electronic structure calculations demonstrate that Fe cations are in the high-spin state of (dz2)2 (dxz, dyz)2 (dxy)1(dx2-y2)1 (S = 2), unlike the previous prediction of (dxz, dyz)3 (dxy)1 (dz2)1 (dx2-y2)1 (S = 2) for SrFeO2, and in the high-spin state of (dxy, dxz, dyz, dx2-y2, z2)5 (S = 5/2) for SrFeO2.5. [ABSTRACT FROM AUTHOR]

Abstract: The structures and stabilities of cage C20F20 and its endohedral complexes X@C20F20 (X=O2−, S2−, Se2−) were determined at the B3LYP/6-31G(d) levels of density functional theory (DFT). It is found that cage C20F20 (I h) possesses of a distinct Cδ+–Fδ− spherical double electric layer, and the adiabatic electron affinity (EA ad) of host cage is higher than that of isolated O atom (2.63 vs. 1.46eV). This suggests the C20F20 cage can selectively trap and stabilize the capsulated spherical anions. The calculations predict that all guest species are minima at the cage center and the corresponding X@C20F20 (I h) complexes have negative inclusion energies (ΔE inc) and thermodynamic parameters (ΔZ). The amount of charge that is being transferred from the encapsulated anions to the cage increases with the atomic radius, i.e., from O2− (∼54%), S2− (∼114%) to Se2−(∼130%), and such a novel model of cage may have practical uses as potential and electrical building units of nanoscale materials. [Copyright &y& Elsevier]

Abstract: The kinetic stability of endohedral X@Si20H20 complexes (X=Li+, Na+, K+, Be2+, Mg2+) has been studied at the B3LYP/6-31G* level of density functional theory (DFT). The transition states (TS) are investigated by the QST3 method of Gaussian 98 package and demonstrated with Intrinsic reaction coordinate (IRC). It is found that K+@Si20H20 cluster has the most stable structure kinetically, that the exit barrier heights (H exit) for K+ expulsion from or insertion in the cage are 187.38 and 205.58kcal/mol, respectively. However, the smallest Be2+ dication is not endohedrally encapsulated and the Be2+@Si20H20 cluster is expected to be the least stable structure kinetically. By comparison, other endohedral complexes have a moderate kinetic stability. [Copyright &y& Elsevier]

Low-lying equilibrium geometric structures of AlnN (n = 1–12) clusters obtained by an all-electron linear combination of atomic orbital approach, within spin-polarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied within the local spin density approximation (LSDA) and the three-parameter hybrid generalized gradient approximation (GGA) due to Becke–Lee–Yang–Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static dipole polarizabilities are calculated for the ground-state structures within the GGA. It is observed that symmetric structures with the nitrogen atom occupying the internal position are lowest-energy geometries. Generalized gradient approximation extends bond lengths as compared with the LSDA lengths. The odd–even oscillations in the dissociation energy, the second differences in energy, the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps, the ionization potential, the electron affinity, and the hardness are more pronounced within the GGA. The stability analysis based on the energies clearly shows the Al7N cluster to be endowed with special stability. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [ABSTRACT FROM AUTHOR]

Abstract: The structure and stability of the neutral cages (M12O36 and M18O54, M=Mo and W) of the Keggin and Wells-Dawson anions have been investigated at the level of density functional theory. These neutral cages can be viewed topologically as polyhedra containing triangles (f 3) and squares (f 4). The relative stability of these polyhedra is determined by the location and separation of the f 3, and the α-Keggin cage without fused triangles (N33=0) is, therefore, more stable than the β isomer with N33=3. This rule is also applicable to the Wells-Dawson cages. The structures and stabilities of these neutral cages mimic those of fullerenes within the framework of isolated pentagon rule. [Copyright &y& Elsevier]

Abstract: The structure and stability of the α/β-[AlW12O40]5− anions have been investigated with seven density functional based methods. It has been found that the relative stability of these anions are sensitive to the density functionals, and the α isomer is more stable than the β one in both gas phase and simulated aqueous medium. This conclusion has also been supported by further calculations on the relative stability of the highly charged α/β-[XW12O40] y− (X=Fe(III), Co(III), Zn(II)) anions. The BP86 incorrect assignment of the α/β-[XW12O40]5− (X=Al, Ga) stability in gas phase can be attributed to the insufficient functional. [Copyright &y& Elsevier]

Abstract: The structure and stability of azido azacycloalkanes, N n (N3) n (n =3–6), have been investigated at the B3LYP/cc-pvTZ level of density functional theory. The stability obeys the gauche effect. The most stable structure is N5(N3)5 (7), while N3(N3)3 (2) is the least stable structure. They are thermodynamically unstable towards dissociation into N2. [Copyright &y& Elsevier]

Abstract: The structure and stability of endohedral X@Si20H20 complexes (X=Li0/+, Na0/+, K0/+, Be0/2+, Mg0/2+, Ca0/2+) have been studied at the B3LYP/6-31G* level of density functional theory. It is found that complexes with X=Na0/+, K0/+, Mg and Ca0/2+ are energy minimum structures with X at the cage center in Ih symmetry, while those with X=Li0/+, Be0/2+, Mg2+ have off-centered structures with X towards one pentagon face in C5v symmetry. Large electron or charge transfer between the Si20H20 cage and the encapsulated X has been observed. [Copyright &y& Elsevier]

Various structural possibilities for AlnN and AlnN2 (n = 1–7) neutral and cationic isomers are investigated, using the density functional method of Becke's three-parameter hybrid exchange functional with the Lee–Yang–Parr nonlocal correlation. Structural optimization and frequency analyses are performed with the basis of 6-311+G(d) for both the neutrals and cations. The calculations predicted the existence of a number of previously unknown isomers (i.e., Al5N2 and Al6N2). The resulting geometries show that the nitrogen atom prefers to be trapped and not to be on the periphery. Frequency analyses indicate that the 3-D Al5N, which was previous proposed as the ground-state structure, is in fact a first-order stationary point with an imaginary frequency at 45i (a2). The optimized ground-state structure of Al5N obtained in this work is a planar configuration with the symmetry of C2v. The calculated adiabatic ionization potentials in their ground states showed that AlN, Al2N, Al3N, and Al4N2 clusters are more stable than any others in AlnN and AlnN2 (n = 1–7) species, being consistent with the observed time-of-flight (TOF) signal intensities. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [ABSTRACT FROM AUTHOR]

Geometric and electronic properties of CmN2 (m = 1-14) clusters have been investigated by density functional theory using the hybrid B3LYP functional and the 6-311G(d) basis set. Harmonic frequencies for these clusters are given to aid in the characterization of the ground states. These results show that CmN2 (m = 1-14) clusters form linear structures with D∞h symmetry. Two N atoms favor to bond at ends in linear isomers. The chains with odd m have triplet ground states whereas the ones with even m have singlet ground states. The calculated HOMO-LUMO gaps and ionization potentials all show that the CmN2 (m = 1-14) clusters with even m are more stable than those with odd m, which is consistent with the observed even-odd alternation of the time-of-fight signal intensities. [ABSTRACT FROM AUTHOR]

B3LYP/6-31G* density functional theory calculations have been carried out on the structure and stability of seven B24N24 clusters. It is found that the new proposed isomer with two octagons, sixteen hexagons and eight squares in S8 symmetry is more stable than the isomer with six octagons, eight hexagons and twelve squares in O symmetry by 60.4 kcal/mol, and the isomer with twenty hexagons and six squares in S4 symmetry by 2.8 kcal/mol. The fullerene-like isomer is much higher in energy (148.6 kcal/mol). [Copyright &y& Elsevier]

Abstract: B3LYP/6-31G* density functional theory calculations have been carried out on the structure and stability of 10 B32N32 clusters. It is found that the new proposed isomer with two octagons, 24 hexagons and eight squares in S8 symmetry is the second most stable structure and less stable than the isomer with 28 hexagons and six squares in C1 symmetry by 6.49kcal/mol. This is similar to B28N28 cluster. [Copyright &y& Elsevier]

The average magnetic moment per atom of Mn13 cluster is expected to be enhanced by doping or coating with a shell. Several ternary core–shell icosahedral clusters TM@Mn12@Au20 were constructed by combining substituting the central Mn with VIII elements (Fe, Co, Ni, Ru, Rh, Pd and Pt) and coating with a icosahedral Au20 shell, and systematically studied by using the first-principles density functional method. Compared to Mn13, Fe@Mn12@Au20 cluster shows a giant enhancement on total magnetic moment (52 µB) which can be greatly attributed to the ferromagnetic coupling between spin moments of atoms. Coating with Au20 shell enlarged the average distances of TM-Mn and Mn-Mn and is a useful way to change the magnetic coupling style. By analysis of density of states and electron localisation functional, we can conclude that the weak hybridisation between Fe and Mn in Fe@Mn12@Au20 is propitious to maintain their original direction of spin moments of atoms and then form ferromagnetic coupling. [ABSTRACT FROM AUTHOR]

Abstract: The hydrogenation of B16N16 cage has been studied using ab initio molecular orbital theory with B3LYP/6-31G(d) method. The structure characters of the most stable B16N16H n (n =2–32) isomers are discussed in detail. The results show that the average binding energies of hydrogenated B16N16 cage are smaller than that of B12N12 cage especially in high hydrogen coverage. The smaller angle distortion and shorter average B–N bond length of B16N16 are the main reason for the smaller average binding energy per H2 of B16N16H n comparing with B12N12H n . Gibbs free energy calculation shows the reaction of B16N16 +16H2 →B16N16H32 will reverse at about 110K, which is lower than the reversing temperature 320K for the reaction of B12N12 +12H2 →B12N12H24. [Copyright &y& Elsevier]

Abstract: One problem with discriminant analysis of microarray data is representation of each sample by a large number of genes that are possibly irrelevant, insignificant or redundant. Methods of variable selection are, therefore, of great significance in microarray data analysis. To circumvent the problem, a new gene mining approach is proposed based on the similarity between probability density functions on each gene for the class of interest with respect to the others. This method allows the ascertainment of significant genes that are informative for discriminating each individual class rather than maximizing the separability of all classes. Then one can select genes containing important information about the particular subtypes of diseases. Based on the mined significant genes for individual classes, a support vector machine with local kernel transform is constructed for the classification of different diseases. The combination of the gene mining approach with support vector machine is demonstrated for cancer classification using two public data sets. The results reveal that significant genes are identified for each cancer, and the classification model shows satisfactory performance in training and prediction for both data sets. [Copyright &y& Elsevier]

Geometries, electronic states and energies of AlnN (n=2–9) have been investigated using the density functional theory (DFT). Structural optimization and frequency analyses were performed with the basis set of 6-311G(d). The N atom prefers to locate on the inside of this series cluster in the ground state except Al6N. Our calculations predicted the existence of a number of previously unknown isomers (i.e. Al9N). Our theoretical investigations also show the Al7N cluster is more stable in this series, which can be explained through s–p hybridization. [Copyright &y& Elsevier]

• Half-metallic quaternary Heusler alloys are found which satisfy the Slater-Pauling rule. • Curie temperatures are well above the room temperature. • A lattice expansion can induce a ferrimagnetism to ferromagnetism phase transition. We have systematically investigated the electronic structures, magnetic properties and strain effects of quaternary Heusler compounds FeMnCrZ (Z = P, As, Sb, Bi, Se, Te) by using the self-consistent full-potential linearized-augmented plane-wave (FPLAPW) method with the generalized gradient approximation (GGA) and the local density approximation (LDA) + U methods based on the density functional theory (DFT). By analyzing the electronic structures of these six compounds within GGA, we have found that the FeMnCrAs, FeMnCrSb, and FeMnCrTe alloys show excellent half-metallic ferrimagnetism, and the FeMnCrP and FeMnCrBi compounds present near half-metallicity. By using the LDA + U method, we found that FeMnCrP, FeMnCrAs and FeMnCrTe are half-metals. The total spin magnetic moments for all the half-metals satisfy the Slater-Pauling 24 electron-rule, confirming the existence of the half-metallic gap. The estimated Curie temperatures of all compounds exceed the room temperature, making the half-metal compounds promising for spintronic applications. Finally, the effects of uniform and tetragonal strain have been investigated. The half-metallicity can be either enhanced, reduced or destroyed by a uniform strain. A ferrimagnetism to ferromagnetism phase transition can be induced by a uniform lattice expansion within the LDA + U method. The effects of the tetragonal distortion turn out to be negligible for these compounds. [ABSTRACT FROM AUTHOR]

The structure and hydrogen adsorption properties of linear HC C-TMH (TM = Sc–Ni) complexes were systematically investigated using a density functional method. The ground states of the HC C-TMH (TM = Sc–Ni) complexes are 2, 3, 4, 3, 4, 3, 2, and 3. The gravimetric H 2 uptake capacities of these ground state HC C-TMH (TM = Sc–Ni) complexes are 4.54–14.56%. Ab initio molecular dynamic simulations indicated that maximal reversible hydrogen storage densities at 77–300 K of the ground state HC C-TMH (TM = Ti–Co) complexes are 6.65–12.00 wt%. The corresponding average adsorption energies are 0.07–0.49 eV. Due to reasonable superior storage capacity and ideal binding energy, HC C-TMH (TM = Ti–Co) complexes are proposed as a suitable hydrogen storage medium at ambient conditions. When HC C-TMH (TM = Ti, V, Cr) are nonground state structures, they can adsorb one more H 2 molecule than their ground states. Unfortunately, the first adsorbed H 2 molecules are dissociated and the adsorption energies are too large. Therefore, the importance of the multiplicity of sorbents for hydrogen storage is emphasized in this work. Image 1 • H 2 storage capacity of HC C-TMH(TM = Sc–Ni) is 4.54–14.56%. • All adsorbed H 2 molecules are in molecular form. • Reversible H 2 storage densities at 77–300 K of HC C-TMH (TM = Ti–Co) are 6.65–12.00%. • Importance of sorbent's multiplicity for H 2 storage study is shown. [ABSTRACT FROM AUTHOR]

The detailed mechanism of the Pd-catalyzed coupling ofnaphthaleneallyl chloride with allenyltributylstannane, resulting in the dearomatizationof the naphthalene group, has been studied using density functionaltheory (DFT) calculations at the B3LYP level. The catalyst cycle canbe divided into three main stages involving oxidative addition, transmetalation,and reductive elimination, none of which contains significantly largebarriers. It is found that the oxidative addition takes place througha monophosphine pathway. The transmetalation step is responsible forthe formation of the propargylic dearomatized product, due to theorientation of the metal-coordinated allenyl ligand. Reductive eliminationof the dearomatized product from the intermediate (η3-allylnaphthalene)(η1-allenyl)PdPH3occursby coupling of the terminal carbon of the η1-allenylligand with the ortho carbon of the η3-naphthaleneligand. Furthermore, it is shown that dichloromethane as solvent doesnot change the mechanistic picture significantly. [ABSTRACT FROM AUTHOR]

Abstract: The geometries, stabilities, electronic and magnetic properties of Co n Rh (n=1–8) clusters have been investigated systematically within the framework of the generalized gradient approximation density-functional theory. The results indicate that the most stable structures of Co n Rh (n=1–8) clusters are all similar to those of corresponding Co n+1 clusters. Maximum peaks of second-order energy difference are found at n=2, 4 and 7, indicating that these clusters possess relatively higher stability than their respective neighbors. The magnetism of the ground state of alloy clusters all displays ferromagnetic coupling except for Co3Rh. In addition, the doped Rh atom exhibits an important influence on the magnetism of alloy clusters, e.g., compared with corresponding pure Co n clusters, the local moment of Co atom is noticeably enhanced in Co n Rh alloy clusters at n=1, 2, 5, 6, 7 and 8, while reduced at n=3 and 4. Further analysis based on the average bond length, the charge transfer and the spin polarization has been made to clarify the different magnetic responses to Rh doping. [Copyright &y& Elsevier]

Abstract: The geometries, stabilities, electronic and magnetic properties of Co13− n M n (n =1, 2, M=Mn, V and Al) clusters have been systematically studied by means of a density functional theory with generalized gradient approximation. The calculated results show that the most stable structures of Co12M and Co11M2 (M=Mn, V and Al) clusters all prefer icosahedral configurations with high symmetry, in which the Mn and Al atoms prefer to occupy surface positions of the icosahedron, while the V atom favors the central position. In these clusters, the Al atoms have nearly zero local magnetic moments, while Mn and V atoms are coupled with the remaining Co atoms ferromagnetically and antiferromagnetically, respectively. These several kinds of different magnetic behaviors result in the total magnetic moment enhancement with doped Mn and reduction with doped V/Al as compared to the optimal icosahedral structure of Co13 cluster, in good agreement with recent Stern–Gerlach experiment results . Analysis based on the binding energy and density of state has been made to clarify different magnetic behaviors of the Co12M and Co11M2 (M=Mn, V and Al) clusters. In addition, our calculations suggest that in the Stern–Gerlach molecular beam the Co12M and Co11M2 (M=Mn, V and Al) alloy clusters mainly exist as icosahedral structures. [Copyright &y& Elsevier]

Abstract: The hydrogenation of endohedral X@B16N16 (X=Li+, Na+, K+, Mg2+, Ne, O2−, S2−, F−, and Cl−) complexes has been studied at the B3LYP/6-31G* level of density functional theory. The structures and properties of the most stable X@B16N16 and X@B16N16H32 complexes along with the size and charge of the endohedral species are discussed comprehensively from the aspects of the average B–N bond lengths, average binding energy per H2 molecule and inclusion energy. On the basis of computational results, it is found that the small and highly charged guest species is favorable for endohedral, and the average binding energies of hydrogenated X@B16N16 complexes are larger than that of B16N16 cage on the whole. Especially, Mg2+ encapsulation is favorable thermodynamically and it could obviously reduce the hydrogen adsorption barriers by 12.05kcal/mol. Also, the reaction of Mg2+@B16N16 +16H2 →Mg2+@B16N16H32 will reverse at 260K, which is higher than the reversing temperature 110K for the reaction of B16N16 +16H2 →B16N16H32. [Copyright &y& Elsevier]

Abstract: The mechanism of the Ni-mediated coupling reaction of CO2 with epoxyethane has been extensively investigated by the density functional theory (DFT) calculations. All the possible pathways are examined, and their corresponding energetics are demonstrated. On the basis of the comparison of three mechanisms, it is determined that the preferred mechanism for the catalytic production of cyclic carbonate can be divided into three main steps involving epoxide oxidative addition, carbon dioxide insertion, and reductive elimination of cyclic carbonate (route IC), none of which contains significantly large barriers. The overall reaction is exothermic and the rate-determining step is associated with the reductive elimination of cyclic carbonate from the six-membered metallacyclic intermediate 15. All reaction pathways with solvent effects taken into consideration have been studied by means of a PCM-UAHF model. The calculations indicate that the introduction of solvent effects does not change the general trends for the reaction potential energy surfaces. Our results provide a theoretical support for the reaction mechanism proposed from previous experimental observations. At the same time, the present theoretical study gives a clear profile for the cycloaddition of carbon dioxide with epoxyethane promoted by (Ph3P)2Ni. [Copyright &y& Elsevier]

Abstract: The geometries, stabilities, electronic and magnetic properties of the (CoRh) n (n ⩽5) clusters have been systematically investigated by using density functional theory with generalized gradient approximation. The calculated results show that the most stable structures of (CoRh) n (n ⩽5) clusters are similar to those of corresponding pure Co2 n and Rh2 n clusters except Rh8, moreover, these ground state structures appear ordered arrangement with higher symmetry. The magnetism of the ground state of alloy clusters all displays ferromagnetic coupling. Compared with corresponding pure Co clusters, the local moment of Co atom has prominent enhancement in CoRh alloy clusters except n =2. The HOMO/LUMO gap of the (CoRh)3 cluster is much smaller than that of its neighboring clusters. In all of the CoRh alloy clusters, the charge always transfers from Co atoms to Rh atoms. [Copyright &y& Elsevier]

Abstract: The equilibrium geometries, electronic states, vibrational frequencies and energies of (GaP) n and (GaP) n − (n =7–9) have been calculated by hybrid B3LYP and B3PW91 functionals at 6-31+G(d) level. The results reveal that the lowest lying electronic states’ geometries of the neutral have the same molecular symmetry as the corresponding anions’. (GaP)7 is shown to have a singlet ground state (1A1) with C 3v symmetry. (GaP)8 is found to be a closed-shell molecule with S 4 symmetry. (GaP)9 takes on a singlet ground state (1A′) with C 3v symmetry. The charge-induced structural changes in these clusters have been discussed. Moreover, natural bond orbital (NBO) analysis implemented to gain insight into the bonding pattern of these clusters indicates these clusters have a partial ionic character. Natural electron configuration shows the extra electron is mostly localized on the metal atoms. In addition, three types of energy separations reported in this work are the adiabatic electron affinity (AEA), the vertical detachment energy (VDE), and the vertical electron affinity (VEA). Herein, adiabatic electron affinities (AEAs) and vertical detachment energies (VDEs) for all of interest are excellent consistent with experiments, as strongly supports the optimized structures. And the order of AEAs and VDEs of the (GaP) n − are both (GaP)9 <(GaP)8 <(GaP)7. (GaP)9 exhibits the lowest adiabatic electron affinity of all the clusters studied, indicating a particularly stable neutral species. [Copyright &y& Elsevier]

• The growth pattern and electronic properties of Cu n (n = 1–14)/TiO 2 (1 1 0) were studied by DFT method. • The supported Cu n (n = 6, 8–14) clusters prefer three-dimensional structures. • The charge transfer from Cu n clusters to TiO 2 surface was observed. • The visible light irradiation can further enhance the charge transfer from the Cu n clusters to TiO 2 surface. The growth pattern and electronic properties of Cu n (n = 1–14) clusters supported on rutile TiO 2 (1 1 0) surface have been studied by using the density functional theory method. The calculation results showed that the supported Cu n (n = 3–5,7) clusters prefer planar or quasi-planar structures, while Cu n (n = 6,8–14) clusters prefer three-dimensional structures. The stabilities of Cu n /TiO 2 show an odd–even oscillation behavior with the increasing n, except n = 2 and 7. For the supported Cu n , the clusters with odd n are more stable than the adjacent clusters. The charge transfer from Cu n clusters to TiO 2 surface was observed. The electron densities of Cu atoms adjacent to O atoms of the surface are obviously reduced. Electronic structure analysis indicated: (1) Electrons are transferred from Cu n clusters to the valence band of TiO 2 surface. (2) The states from Cu n clusters appear in the energy gap of the TiO 2 surface and the energy gaps between the occupied states from Cu n clusters and the unoccupied states from TiO 2 surface decrease with the increasing n. Our calculations showed that the visible light irradiation can further enhance the charge transfer from the Cu n clusters (with diameter smaller than 0.6 nm) to TiO 2 surface and facilitate the reduction reactions (such as CO 2 reduction reaction) on the TiO 2 surface. [ABSTRACT FROM AUTHOR]