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1.
The present study reports the geometries, electronic structures, growth behavior, and stabilities of neutral and ionized copper-doped germanium clusters containing 1–20 Ge atoms within the framework of linear combination of atomic orbitals density functional theory (DFT) under the spin-polarized generalized gradient approximation. It was found that Cu-capped Ge n (or Cu-substituted Ge n+1) and Cu-encapsulated Ge n clusters mostly occur in the ground state at a particular cluster size (n). In order to explain the relative stabilities of the ground-state clusters, parameters such as the average binding energy per atom (BE), the embedding energy (EE), and the fragmentation energy (FE) of the clusters were calculated, and the resulting values are discussed. To explain the chemical stabilities of the clusters, parameters such as the energy gap between the highest occupied and the lowest unoccupied molecular orbitals (the HOMO–LUMO gap), the ionization energy (IP), the electron affinity (EA), the chemical potential (μ), the chemical hardness (η), and the polarizability were calculated, and the resulting values are also discussed. Natural atomic orbital (NAO) and natural bond orbital (NBO) analyses were also used to determine the electron-counting rule that should be applied to the most stable Ge10Cu cluster. Finally, the relevance of the calculated results to the design of Ge-based superatoms is discussed.
Figure Contributions of the valance orbitals of the Ge and Cu atom(s) to the HOMO of the ground-state icosahedral Ge10Cu cluster obtained from NBO analysis. The numbers below the clusters represent the occupancies of the HOMO orbitals
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2.
Physical and chemical adsorption of CO2 on ZnO surfaces were studied by means of two different implementations of periodic density functional theory. Adsorption energies were computed and compared to values in the literature. In particular, it was found that the calculated equilibrium structure and internuclear distances are in agreement with previous work. CO2 adsorption was analyzed by inspection of the density of states and electron localization function. Valence bands, band gap and final states of adsorbed CO2 were investigated and the effect of atomic displacements analyzed. The partial density of states (PDOS) of chemical adsorption of CO2 on the ZnO(0001) surface show that the p orbitals of CO2 were mixed with the ZnO valence band state appearing at the top of the valence band and in regions of low-energy conduction band.
Figure
ELF analysis of bidentate and tridentate chemical adsorptions  相似文献   

3.
In our quest to explore molecules with chemically significant regions where the Fukui function is negative, we explored reactions where the frontier orbital that indicates the sites for electrophilic attack is not the highest occupied molecular orbital. The highest occupied molecular orbital (HOMO) controls the location of the regions where the Fukui function is negative, supporting the postulate that negative values of the Fukui function are associated with orbital relaxation effects and nodal surfaces of the frontier orbitals. Significant negative values for the condensed Fukui function, however, were not observed.
Figure
The ?10?5isosurface of $ {f^{-}}\left( \mathbf{r} \right) $ (opaque silver surface) traces the nodal regions of the HOMO (translucent colored lobes, with different colors for different phases) of the phenoxide anion  相似文献   

4.
MP2(full)/6-311++G(3df,3pd) calculations were carried out on complexes linked through various non-covalent Lewis acid – Lewis base interactions. These are: hydrogen bond, dihydrogen bond, hydride bond and halogen bond. The quantum theory of ´atoms in molecules´ (QTAIM) as well as the natural bond orbitals (NBO) method were applied to analyze properties of these interactions. It was found that for the A-H…B hydrogen bond as well as for the A-X…B halogen bond (X designates halogen) the complex formation leads to the increase of s-character in the A-atom hybrid orbital aimed toward the H or X atom. In opposite, for the A…H-B hydride bond, where the H-atom possesses negative charge, the decrease of s-character in the B-atom orbital is observed. All these changes connected with the redistribution of the electron charge being the effect of the complex formation are in line with Bent´s rule. The numerous correlations between energetic, geometrical, NBO and QTAIM parameters were also found.
Figure
QTAIM atomic radii for NH4 +…HMgH and Na+…HBeH  相似文献   

5.
The structure, spectral properties and the hydrogen bond interactions of 8-aza analogues of xanthine, theophylline and caffeine have been studied by using quantum chemical methods. The time-dependent density functional theory (TD-DFT) and the singly excited configuration interaction (CIS) methods are employed to optimize the excited state geometries of isolated 8-azaxanthine, 8-azatheophylline tautomers and 8-azacaffeine in both the gas and solvent phases. The solvent phase calculations are performed using the polarizable continuum model (PCM). The absorption and emission spectra are calculated using the time-dependent density functional theory (TD-DFT) method. The results from the TD-DFT calculations reveal that the excitation spectra are red shifted relative to absorption in aqueous medium. These changes in the transition energies are qualitatively comparable to the experimental data. The examination of molecular orbital reveals that the molecules with a small H→L energy gap possess maximum absorption and emission wavelength. The relative stability and hydrogen bonded interactions of mono and heptahydrated 8-azaxanthine, 8-azatheophylline tautomers and 8-azacaffeine have been studied using the density functional theory (DFT) and Møller Plesset perturbation theory (MP2) implementing the 6-311++G(d,p) basis set. The formation of strong N-H…O bond has resulted in the highest interaction energy among the monohydrates. Hydration does not show any significant impact on the stability of heptahydrated complexes. The atoms in molecule (AIM) and natural bonding orbital (NBO) analyses have been performed to elucidate the nature of the hydrogen bond interactions in these complexes.
Figure
Absorption and emission spectra of 8-aza analogues of xanthine, theophylline and caffeine in methanol medium  相似文献   

6.
We calculate the interactions of two atomic layer deposition (ALD) reactants, trimethylaluminium (TMA) and tetrakis(ethylmethylamino) hafnium (TEMAH) with the hydroxylated Ga-face of GaN clusters when aluminum oxide and hafnium oxide, respectively, are being deposited. The GaN clusters are suitable as testbeds for the actual Ga-face on practical GaN nanocrystals of importance not only in electronics but for several other applications in nanotechnology. We find that TMA spontaneously interacts with hydroxylated GaN; however it does not follow the atomic layer deposition reaction path unless there is an excess in potential energy introduced in the clusters at the beginning of the optimization, for instance, using larger bond lengths of various bonds in the initial structures. TEMAH also does not interact with hydroxylated GaN, unless there is an excess in potential energy. The formation of a Ga—N(CH3)(CH2CH3) bond during the ALD of HfO2 using TEMAH as the reactant without breaking the Hf—N bond could be the key part of the mechanism behind the formation of an interface layer at the HfO2/GaN interface.
Figure
Interactions of TMA and TEMAH with hydroxylated GaN  相似文献   

7.
A combined and sequential use of quantum mechanical (QM) calculations and classical molecular dynamics (MD) simulations was made to investigate the σ and π types of hydrogen bond (HB) in benzene-water and pyrrole-water as clusters and as their liquid mixture, respectively. This paper aims at analyzing similarities and differences of these HBs resulted from QM and MD on an equal footing. Based on the optimized geometry at ωb97xD/aug-cc-pVTZ level of theory, the nature and property of σ and π types of HBs are unveiled by means of atoms in molecules (AIM), natural bond orbital (NBO) and energy decomposition analysis (EDA). In light of the above findings, MD simulation with OPLS-AA and SPC model was applied to study the liquid mixture at different temperatures. The MD results further characterize the behavior and structural properties of σ and π types HBs, which are somewhat different but reasonable for the clusters by QM. Finally, we provide a reasonable explanation for the different solubility between benzene/water and pyrrole/water.
Figure
The σ and π types of hydrogen bond as benzene-water and pyrrole-water clusters in gas; Snapshot of benzene/water and pyrrole/water as 1:1 liquid mixture extracted from the MD simulations  相似文献   

8.
The preferential interactions of glycine betaine (GB) with solvent components and the effect of solvent on its stability have been examined. In particular, the microsolvation of organic osmolyte and widely important osmoprotectant in nature as glycine betaine has been reported by using M06 method. A number of configurations (bX (a-z)) of the clusters for one to seven water molecules (×?=?1-7) have been considered for the microsolvation. Structures of stable conformers are obtained and denoted as b1a, b2a, b3a, b4a, b5a, b6a and b7a. It is observed from the interaction energy difference (?E) that only seven water molecules can be accommodated in the first solvation shell to stabilize GB. It is also observed that the calculated relative energy using M06 is in close agreement with calculations at the MP2 level of theory.
Figure
Graphical abstract illustrating the significance of the paper  相似文献   

9.
A theoretical investigation is completed on the mechanism of electrical breakdown strength increment of polyethylene. It is shown that it is one of the most important factors for increasing electrical breakdown strength of polyethylene through keto-enol isomerization of acetophenone and its analogues at the ground state S0 and the lowest triplet state T1. The minimum structures and transition states of the keto- and the enol-tautomer of acetophenone and its analogues at the S0 and T1 states are obtained at the B3LYP/6-311+G(d,p) level, as well as the harmonic vibration frequencies of the equilibrium geometries and the minimum energy path (MEP) by the intrinsic reaction coordinate (IRC) theory at the same level. The two C–C bond cleavage reaction channels have been identified in acetophenone. The calculated results show that the energy barriers of keto-enol isomerization of acetophenone and its analogues at S0 and T1 states are much smaller than the average C-C bond energy of polyethylene, and the acetophenone doping or bond linked into polyethylene can increase the electrical breakdown strength and inhibit polyethylene electrical tree initiation and aging.
Figure
Potential energy surface of keto-enol isomerization reaction of acetophenone has been investigated. The mechanism of electrical breakdown strength increment of cross-linking polyethylene has been explained. It is expected to provide reliable reference information for preparating the insulation material of high-voltage cable exceed 500 kV.  相似文献   

10.
The geometric and electronic structures, absorption spectra, transporting properties, chemical reactivity indices and electrostatic potentials of the planar three-coordinate organoboron compounds 1-2 and twisted reference compound Mes 3 B, have been investigated by employing density functional theory (DFT) and conceptual DFT methods to shed light on the planarity effects on the photophysical properties and the chemical reactivity. The results show that the planar compounds 1-2 exhibit significantly lower HOMO level than Mes 3 B, owing to the stronger electronic induction effect of boron centers. This feature conspicuously induces a blue shifted absorption for 1, although 1 seemingly possesses more extended conjugation framework than Mes 3 B. Importantly, the reactivity strength of the boron atoms in 1-2 is much lower than that in Mes 3 B, despite the fact that the tri-coordinate boron centers of 1-2 are completely naked. The interesting and abnormal phenomenon is caused by the strong p-π electronic interactions, that is, the empty p-orbital of boron center is partly filled by π-electron of the neighbor carbon atoms in 1-2, which are confirmed by the analysis of Laplacian of the electron density and natural bond orbitals. Furthermore, the negative electrostatic potentials of the boron centers in 1-2 also interpret that they are not the most preferred sites for incoming nucleophiles. Moreover, it is also found that the planar compounds 1-2 can act as promising electron transporting materials since the internal reorganization energies for electron are really small.
Figure
The planar effects significantly affect the frontier molecular orbital levels, absorption wavelengths, transporting properties, and chemical reactivities of compounds 1-2. The underlying origin has been revealed by density functional theory and conceptual density functional theory calculations  相似文献   

11.
This paper presents an ab initio quantum chemical investigation of the geometrical structures and the non-linear optical properties (NLO) of three structural isomers of pyridinium N-phenolate betaine dye. The ground state geometrical parameters and the first-order hyperpolarizabilities were calculated using the Hartree-Fock (HF) as well as the second-order perturbation Møller-Pleset (MP2) method with the 6–31G, 6–31G(d), 6–31G(d,p), 6–31+G(d), 6–31++G(d,p), 6–311+G(d), aug-cc-PVDZ and the recently developed Z3PolX basis sets. Moreover, the first-order hyperpolarizability was calculated at the coupled cluster singles and doubles (CCSD/6–31+G(d)) level of theory. The analysis of the results of calculations for the investigated isomers indicates that there are important differences in their NLO activities. Additionally, it was shown that Z3PolX basis set works reasonable well for betaine dyes.
Figure
The molecules investigated in the present study. (Figure prepared using Mercury 1.5.)  相似文献   

12.
Gas-phase reactions of ClO/BrO with RCl (R = CH3, C2H5, and C3H7) have been investigated in detail using the popular DFT functional BHandHLYP/aug-cc-pVDZ level of theory. As a result, our findings strongly suggest that the type of reaction is firstly initiated by a typical SN2 fashion. Subsequently, two competitive substitution steps, named as SN2-induced substitution and SN2-induced elimination, respectively, would proceed before the initial SN2 product ion-dipole complex separates, in which the former exhibits less reactivity than the latter. Those are consistent with relevant experimental results. Moreover, we have also explored reactivity difference for the title reactions in term of some factors derived from methyl group, p-π electronic conjugation, ionization energy (IE), as well as molecular orbital (MO) analysis.
Figure
Energy profiles for the ClO– reactions and BrO–reactions, respectively  相似文献   

13.
14.
The equilibrium structures, spectroscopic and thermodynamic parameters [entropy (S), internal energy (E), heat capacity (C p)] of U2, U2O, U2O2 and U2O4 uranium oxide molecules were investigated systematically using density functional theory (DFT). Our computations indicated that the ground electronic state of U2 is the septet state and the equilibrium bond length is 2.194 Å; the ground electronic state of U2O and U2O2 were found to be $ {\tilde{X}}^3\varPhi $ and $ {\tilde{X}}^3{\sum}_{\mathrm{g}} $ with stable C ∞v and D ∞h linear structures, respectively. The bridge-bonded structure with D 2h symmetry and $ {\tilde{X}}^3{\mathrm{B}}_{1\mathrm{g}} $ state is the most stable configuration for the U2O4 molecule. Mulliken population analyses show that U atoms always lose electrons to become the donor and O atoms always obtain electrons as the acceptor. Molecular orbital analyses demonstrated that the frontier orbitals of the title molecules were contributed mostly by 5f atomic orbitals of U atoms. Vibrational frequencies analyses indicate that the maximum absorption peaks stem from the stretching mode of U–O bonds in U2O, U2O2 and U2O4. In addition, thermodynamic data of U2On (n?=?0?~?4) molecules at elevated temperatures of 293.0 K to 393.0 K was predicted.  相似文献   

15.
The reaction force and the electronic flux, first proposed by Toro-Labbé et al. (J Phys Chem A 103:4398, 1999) have been expressed by the existing conceptual DFT apparatus. The critical points (extremes) of the chemical potential, global hardness and softness have been identified by means of the existing and computable energy derivatives: the Hellman-Feynman force, nuclear reactivity and nuclear stiffness. Specific role of atoms at the reaction center has been unveiled by indicating an alternative method of calculation of the reaction force and the reaction electronic flux. The electron dipole polarizability on the IRC has been analyzed for the model reaction HF + CO→HCOF. The electron polarizability determined on the IRC α e (ξ) was found to be reasonably parallel to the global softness curve S(ξ). The softest state on the IRC (not TS) coincides with zero electronic flux.
Figure
Variation of the electronic dipole polarizability  相似文献   

16.
Calculations performed at the ab initio level using the recently reported planar concentric π-aromatic B18H6 2+(1) [Chen Q et al. (2011) Phys Chem Chem Phys 13:20620] as a building block suggest the possible existence of a new class of B3n H m polycyclic aromatic hydroboron (PAHB) clusters—B30H8(2), B39H9 2?(3), B42H10(4/5), B48H10(6), and B72H12(7)—which appear to be the inorganic analogs of the corresponding C n H m polycyclic aromatic hydrocarbon (PAHC) molecules naphthalene C10H8, phenalenyl anion C13H9 ?, phenanthrene/anthracene C14H10, pyrene C16H10, and coronene C24H12, respectively, in a universal atomic ratio of B:C?=?3:1. Detailed canonical molecular orbital (CMO), adaptive natural density partitioning (AdNDP), and electron localization function (ELF) analyses indicate that, as they are hydrogenated fragments of a boron snub sheet [Zope RR, Baruah T (2010) Chem Phys Lett 501:193], these PAHB clusters are aromatic in nature, and exhibit the formation of islands of both σ- and π-aromaticity. The predicted ionization potentials of PAHB neutrals and electron detachment energies of small PAHB monoanions should permit them to be characterized experimentally in the future. The results obtained in this work expand the domain of planar boron-based clusters to a region well beyond B20, and experimental syntheses of these snub B3n H m clusters through partial hydrogenation of the corresponding bare B3n may open up a new area of boron chemistry parallel to that of PAHCs in carbon chemistry.
Figure
Ab initio calculations predict the existence of polycyclic aromatic hydroboron clusters as fragments of a boron snub sheet; these clusters are analogs of polycyclic aromatic hydrocarbons  相似文献   

17.
The properties of noble gas systems can be greatly extended by heterogeneous mixtures of elements. The geometrical structures and energies of mixed Ar–Kr–Xe clusters were investigated using ternary Lennard-Jones (TLJ) potential. For the Ar19Kr n Xe19, Ar19Kr19Xe n , and Ar n Kr19Xe19 (n?=?0–17) clusters investigated, the results show that only two minimum energy configurations exist, i.e., polytetrahedron and six-fold pancake. The inner core of all these clusters is composed mainly of Ar atoms, and Kr and Xe atoms are distributed on the surface with well mixed pattern for polytetrahedral and segregate pattern for six-fold pancake configurations. The relative stability property of Ar–Kr–Xe clusters with a certain composition is discussed. Moreover, the role of heterogeneity on the strain was investigated, and reduced strain energies in Ar–Kr–Xe clusters were studied to find possible ways of reducing strain. The results showed that the strain energies were affected mainly by Ar–Ar, Ar–Kr, and Xe–Xe bonds.
Figure
Investigation of the structures of Ar19Kr n Xe19, Ar19Kr19Xe n , and Ar n Kr19Xe19 (n?=?0–17) clusters reveal the existence of only exist two minimum energy configurations, i.e., polytetrahedron and six-fold pancake. Furthermore, reduced strain energies in Ar–Kr–Xe clusters were studied for the possible ways of reducing strain.  相似文献   

18.
To understand the chemical behavior of uranyl complexes in water, a bis-uranyl [(phen)(UO2)(μ2–F)(F)]2 (A; phen?=?phenanthroline, μ2?=?doubly bridged) and its hydrated form A?·?(H2O)n (n?=?2, 4 and 6) were examined using scalar relativistic density functional theory. The addition of water caused the phen ligands to deviate slightly from the U22–F)2 plane, and red-shifts the U–F-terminal and U?=?O stretching vibrations. Four types of hydrogen bonds are present in the optimized hydrated A?·?(H2O)n complexes; their energies were calculated to fall within the range 4.37–6.77 kcal mol-1, comparable to the typical values of 5.0 kcal mol-1 reported for hydrogen bonds. An aqueous environment simulated by explicit and/or implicit models lowers and re-arranges the orbitals of the bis-uranyl complex.
Figure
A bis(uranyl) complex [(phen)(UO2)(μ2–F)(F)]2 (A) and its solvated form A?·?(H2O)n were examined using scalar relativistic density functional theory. Hydrogen bonds cause the phen ligand to slightly deviate from the equatorial plane of the uranyl ion, resulting in a pronounced red-shift of the U–F-terminal and U?=?O asymmetric stretching vibrations. The calculated energies fall within 4.4?–6.8 kcal/mol. Explicit and/or implicit aqueous solvation re-arranges the molecular orbitals of the complex  相似文献   

19.
Quantum chemical calculations were performed for LiNH2–HMgX (X?=?H, F, Cl, Br, CH3, OH, and NH2) complexes to propose a new interaction mechanism between them. This theoretical survey showed that the complexes are stabilized through the combinative interaction of magnesium and lithium bonds. The binding energies are in the range of 63.2–66.5 kcal mol?1, i.e., much larger than that of the lithium bond. Upon complexation, both Mg–H and Li–N bonds are lengthened. Substituents increase Mg-H bond elongation and at the same time decrease Li-N bond elongation. These cyclic complexes were characterized with the presence of a ring critical point and natural population analysis charges.
Figure
A new interaction mechanism has been suggested for the LiNH2-HMgH complex. It was found that the combinative interaction of magnesium and lithium bonds is responsible for the stability of the complex. The effect of subsitutents on its stability has also been investigated  相似文献   

20.
Quantum chemical calculations are performed to study the interplay between halogen?nitrogen and halogen?carbene interactions in NCX?NCX?CH2 complexes, where X?=?F, Cl, Br and I. Molecular geometries and interaction energies of dyads and triads are investigated at the MP2/aug-cc-pVTZ level of theory. It is found that the X?N and X?Ccarbene interaction energies in the triads are larger than those in the dyads, indicating that both the halogen bonding interactions are enhanced. The estimated values of cooperative energy E coop are all negative with much larger E coop in absolute value for the systems including iodine. The nature of halogen bond interactions of the complexes is analyzed using parameters derived from the quantum theory atoms in molecules methodology and energy decomposition analysis.
Figure
The structure of NCX?NCX?CH2 complexes (X?=?F, Cl, Br and I)  相似文献   

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