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1.
J Phys Chem Lett ; 10(20): 6360-6367, 2019 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-31573207

RESUMO

The potassium-ion battery (KIB), as one of the most promising alternatives to the lithium-ion battery (LIB), has recently received considerable attention. One of the challenges in KIBs is the design and synthesis of high-performance anode materials with high capacity, high rate performance, and good cycling stability. Here, on the basis of first-principles calculations, we propose a three-dimensional (3D) porous nodal-line semimetal carbon allotrope, named BDL-14, consisting of benzene rings incorporated into the diamond lattice, as a potential candidate. With low mass density (1.41 g/cm3), ordered channels, high carrier velocity (0.83 × 106 m/s), high specific capacity (478.23 mAh/g), very low energy barriers (0.05-0.08 eV) for K-ion diffusion, and a small volume expansion (7.03%) during charging and discharging processes, BDL-14 can surpass the properties of anodes currently being considered.

2.
J Phys Chem A ; 122(22): 5043-5049, 2018 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-29746132

RESUMO

Motivated by the fact that Fe2O3 nanoparticles are used in the treatment of cancer, we have examined the role of ligands on the magnetic properties of these particles by focusing on (Fe2O3)4 as a prototype system with H as ligands. Using the Broken-Symmetry Density Functional Theory, we observed a strong collective superexchange in the hydrogenated Fe8O12H8 cluster. The average antiferromagnetic exchange coupling constant between the four iron-iron oxo-bridged pairs was found to be -178 cm-1, whereas coupling constants between hydroxo-bridged pairs were much smaller. We found that despite the apparent symmetry of the iron atom framework, it is not reasonable to assume this symmetry when fitting the exchange coupling constants. We also analyzed the geometrical and magnetic properties of Fe8O12H n for n = 0-12 and found that hydrogenating oxo-bridges would generally inhibit the Fe-O-Fe antiferromagnetic superexchange interactions. Antiferromagnetic lowest total energy states become favorable only when specific distributions of hydrogen atoms are realized. The (HO)4-Fe4(all spin-up)-O4-Fe4(all spin-down)-(OH)4 configuration in Fe8O12H8 presents such an example. This symmetric configuration can be considered a superdiatomic system.

3.
Phys Chem Chem Phys ; 20(6): 4546-4553, 2018 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-29376164

RESUMO

The structure and properties of the Fe8O12Hn clusters (n = 0-18) are computed using the all-electron density functional theory with the generalized gradient approximation for the exchange-correlation potential. The ground state of Fe8O12 is found to be a singlet state having a bi-capped octahedron geometry. Upon hydrogenation, the octahedral framework of Fe is retained in Fe8O12Hn up to n < 7, beyond which point the iron octahedron transforms into a cube. Hydrogen atoms are bound to oxygen atoms up to n = 12, but they bind to the faces of the Fe8 cube when n > 12. The total spin magnetic moment of a Fe8O12Hn cluster is larger than 6 µB for 1 ≤ n ≤ 18, except for n = 8 and 10, where the lowest total energy states are antiferromagnetic singlets. The reason for this deviation from the general behavior in the Fe8O12Hn series is attributed to the collective superexchange phenomenon. Surprisingly, the total spin magnetic moment of a Fe8O12Hn cluster is found to be substantially larger than the total spin magnetic moment of the bare Fe8 cluster when n = 12-18. All of the Fe8O12Hn clusters are stable with respect to an abstraction of a single hydrogen atom but are unstable toward the abstraction of an H2 dimer when n =10 and n = 14-18.

4.
J Phys Chem A ; 121(44): 8414-8424, 2017 Nov 09.
Artigo em Inglês | MEDLINE | ID: mdl-29035556

RESUMO

Using both mass spectrometry with intense femtosecond laser ionization and high-level computational methods, we have explored the structure and fragmentation patterns of dimethyl methylphosphonate (DMMP) cation. Extensive search of the geometries of both neutral and positively charged DMMP yields new isomers that are appreciably lower in total energy than those commonly synthesized using the Michaelis-Arbuzov reaction. The stability of the standard isomer with CH3PO(OCH3)2 topology is found to be due to the presence of high barriers to isomer interconversion that involves several transition states. Our femtosecond laser ionization experiments show that the relative yields of the major dissociation products as a function of peak laser intensity correlate well with the theoretical estimates for the energies of the DMMP+ decay via various channels. In contrast, the peak laser intensities required for observation of minor dissociation products exhibit no correlation with the computed decay energies, which suggests that barrier heights and/or excited electronic states of DMMP+ determine its preferred fragmentation pathways in an intense femtosecond laser field.

5.
Chem Commun (Camb) ; 53(75): 10402-10405, 2017 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-28880329

RESUMO

Applying Le Chatelier's principle, a one-pot synthesis method is reported that generates highly anisotropic hedgehog gold nanoparticles (HHogGNPs), undemanding of a preformed seed or surfactant. These non-toxic HHogGNPs are potent candidates for nanomedicinal applications owing to their broad-band plasmon tunability, gigantic Raman enhancement and remarkable retention in a highly salted physiological environment.

6.
Nanoscale ; 8(44): 18760-18770, 2016 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-27801449

RESUMO

Herein the photophysical properties of hydrogenated fullerenes (fulleranes) synthesized by direct hydrogenation utilizing hydrogen pressure (100 bar) and elevated temperatures (350 °C) are compared to the fulleranes C60H18 and C60H36 synthesized by amine reduction and the Birch reduction, respectively. Through spectroscopic measurements and density functional theory (DFT) calculations of the HOMO-LUMO gaps of C60Hx (0 ≤ x ≤ 60), we show that hydrogenation significantly affects the electronic structure of C60 by decreasing conjugation and increasing sp3 hybridization. This results in a blue shift of the emission maximum as the number of hydrogen atoms attached to C60 increases. Correlations in the emission spectra of C60Hx produced by direct hydrogenation and by chemical methods also support the hypothesis of the formation of C60H18 and C60H36 during direct hydrogenation with emission maxima of 435 and 550 nm respectively. We also demonstrate that photophysical tunability, stability, and solubility of C60Hx in a variety of organic solvents make them easily adaptable for application as luminescent down-shifters in heads-up displays, light-emitting diodes, and luminescent solar concentrators. The utilizization of carbon based materials in these applications can potentially offer advantages over commonly utilized transition metal based quantum dot chromophores. We therefore propose that the controlled modification of C60 provides an excellent platform for evaluating how individual chemical and structural changes affect the photophysical properties of a well-defined carbon nanostructure.

7.
Phys Chem Chem Phys ; 17(40): 26589-93, 2015 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-26394536

RESUMO

Superhalogens belong to a class of molecules that not only mimic the chemistry of halogen atoms but also possess electron affinities that are much larger than that of chlorine, the element with the highest electron affinity in the periodic table. Using BO2 as an example and the synergy between density functional theory-based calculations and photoelectron spectroscopy experiments we demonstrate another unusual property of superhalogens. Unlike halogens, whose ability to accept an electron falls upon dimerization, B2O4, the dimer of BO2, has an electron affinity larger than that of the BO2 building block. This ability of (BO2)2 and subsequent, higher oligomers (BO2)n (n = 3 and 4), to retain their superhalogen characteristics can be traced to the enhanced bonding interactions between oxygen and boron atoms and due to the delocalization of the charge of the extra-electron over the terminal oxygen atoms. These results open the door to the design and synthesis of a new class of metal-free highly negative ions with potential for novel applications.


Assuntos
Compostos de Boro/química , Halogênios/química , Elétrons , Espectroscopia Fotoeletrônica , Teoria Quântica
8.
J Phys Chem A ; 119(24): 6483-92, 2015 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-25974113

RESUMO

The electronic and geometrical structures of the neutral Fn and singly negatively charged Fn(-) polyfluorides (n = 3-29) are studied using three levels of theory: density functional theory (DFT) with generalized gradient approximation, hybrid Hartree-Fock-DFT, and hybrid HF-DFT with long-range corrections. For n > 4, each polyfluoride possesses a number of states with different geometries that are closely spaced in total energy. The geometrical structures of the lowest total energy states follow different patterns for the even-n and odd-n Fn(-) anion branches with a preference for higher symmetry geometries. The largest F29(-) anion considered is found to possess Oh symmetry. All the anions beginning with F3(-) are found to possess adiabatic and vertical electron detachment energies exceeding the electron affinities of halogen atoms and are therefore superhalogen anions. Electron affinities, energies of formation, and binding energies show oscillatory behavior as functions of the number n of fluorine atoms. The neutral Fn species are found to be barely stable and are bound by polarization forces. The Fn(-) anions, on the contrary, are quite stable toward the loss of F, F(-), and F2(-), but not to the loss of F2.

9.
J Chem Phys ; 140(5): 054301, 2014 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-24511934

RESUMO

Through a synergetic combination of anion photoelectron spectroscopy and density functional theory based calculations, we have established that aluminum moieties within selected sodium-aluminum clusters are Zintl anions. Sodium-aluminum cluster anions, Na(m)Al(n)(-), were generated in a pulsed arc discharge source. After mass selection, their photoelectron spectra were measured by a magnetic bottle, electron energy analyzer. Calculations on a select sub-set of stoichiometries provided geometric structures and full charge analyses for both cluster anions and their neutral cluster counterparts, as well as photodetachment transition energies (stick spectra), and fragment molecular orbital based correlation diagrams.

10.
J Phys Chem A ; 118(37): 8158-62, 2014 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-24512169

RESUMO

The alanate anion, AlH4(-), was generated in the gas phase using a pulsed arc cluster ionization source. Its photoelectron spectrum was then measured with 193 nm photons. The spectrum consists of a broad feature, spanning electron binding energies from 3.8 eV to over 5.3 eV. This band reflects the photodetachment transitions between the ground state of the AlH4(-) anion and the ground state of its thermodynamically unstable neutral counterpart, AlH4. The vertical detachment energy (VDE) of AlH4(-) was measured to be 4.4 eV. Additionally, VDE values were also computed in a comprehensive theoretical study and compared both with the previously computed value and with our experimentally determined value.

11.
J Chem Phys ; 138(16): 164303, 2013 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-23635134

RESUMO

The electronic and geometrical structures of the M12 and M13 clusters where M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn along with their singly negatively and positively charged ions are studied using all-electron density functional theory within the generalized gradient approximation. The geometries corresponding to the lowest total energy states of singly and negatively charged ions of V13, Mn12, Co12, Ni13, Cu13, Zn12, and Zn13 are found to be different from the geometries of the corresponding neutral parents. The computed ionization energies of the neutrals, vertical electron detachment energies from the anions, and energies required to remove a single atom from the M13 and M13(+) clusters are in good agreement with experiment. The change in a total spin magnetic moment of the cation or anion with respect to a total spin magnetic moment of the corresponding neutral is consistent with the one-electron model in most cases, i.e., they differ by ±1.0 µ(B). Exceptions are found only for Sc12(-), Ti12(+), Mn12(-), Mn12(+), Fe12(-), Fe13(+), and Co12(+).


Assuntos
Metais Pesados/química , Teoria Quântica , Estrutura Molecular
12.
J Phys Chem Lett ; 4(20): 3382-6, 2013 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-26705581

RESUMO

The Mn atom, because of its special electronic configuration of 3d(5)4s(2), has been widely used as a dopant in various two-dimensional (2D) monolayers such as graphene, BN, silicene and transition metal dichalcogenides (TMDs). The distributions of doped Mn atoms in these systems are highly sensitive to the synthesis process and conditions, thus suffering from problems of low solubility and surface clustering. Here we show for the first time that the MnO2 monolayer, synthetized 10 years ago, where Mn ions are individually held at specific sites, exhibits intrinsic ferromagnetism with a Curie temperature of 140 K, comparable to the highest TC value achieved experimentally for Mn-doped GaAs. The well-defined atomic configuration and the intrinsic ferromagnetism of the MnO2 monolayer suggest that it is superior to other magnetic monolayer materials.

13.
J Phys Chem A ; 117(6): 1310-8, 2013 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-23116139

RESUMO

Using density functional theory based calculations, we have systematically studied the equilibrium geometries, relative stabilities, and electronic and magnetic properties of Fe and Mn atoms interacting with a varying number of BO(2) moieties. These clusters are found to exhibit hyperhalogen behavior with electron affinities as high as 6.9 eV once the number of BO(2) moieties exceed the nominal valences of these transition metals toms, namely 2 for both Fe and Mn. In all cases the transition metal atoms retain a sizable spin magnetic moment, even exceeding their free atom values at certain compositions. We also note that when more than two BO(2) moieties are bound to neutral Fe and Mn atoms, they tend to dimerize. In the case of negative ions, this process occurs at n ≥ 3, thus leading to different neutral and anionic ground state geometries. The effect of these structural changes in the interpretation of photoelectron spectroscopy experiments is discussed.


Assuntos
Compostos de Boro/química , Ferro/química , Manganês/química , Elétrons , Campos Magnéticos , Teoria Quântica
14.
J Phys Chem A ; 116(41): 10218-28, 2012 Oct 18.
Artigo em Inglês | MEDLINE | ID: mdl-23039843

RESUMO

The electronic and geometrical structures of the Fe(n), Fe(n)(­), and Fe(n)(+) series (n = 7­20) are studied using all-electron density functional theory with the generalized gradient approximation. Equilibria of the geometrical configurations of the lowest total energy states in all three series are found to be similar except for Fe(9)(­), Fe(9)(+), Fe(10)(­), Fe(10)(+), Fe(15)(­), and Fe(19)(+). Our computed ionization energies of the neutrals, vertical electron detachment energies, and energies of Fe atom abstraction are in good agreement with experiment. It is found that the one-electron model corresponding to the change in the total magnetic moment of ±1.0µ(B) due to either attachment or detachment of an electron is valid in most cases. The exceptions are Fe(4)(+), Fe(10)(­), Fe(10)(+), Fe(12)(­), Fe(13)(+), and Fe(14)(+), where the change in the total magnetic moment is +3µ(B) (Fe(10)(­) and Fe(12)(­)), −3µ(B) (Fe(4)(+), Fe(11)(+), and Fe(14)(+)), and −9µ(B) (Fe(13)(+)). The reason for an anomalously large quenching of the total spin magnetic moment in Fe(13)(+) is explained. Our computed total spin magnetic moments per atom match the recent experimental values within the experimental uncertainty bars.

15.
J Phys Chem A ; 116(5): 1469-74, 2012 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-22216941

RESUMO

Halogens possess among the highest electron affinities of elements in the periodic table. Superhalogen molecules with electron affinities higher than those of halogen atoms have been known to form when a metal atom is surrounded with halogen atoms. Recently, it was discovered that a new class of molecules called hyperhalogens with electron affinities higher than those of superhalogens can form when the latter serve as the building block. By use of density functional theory and B3LYP hybrid exchange-correlation functional we show that molecules with electron affinities even higher can be formed by using hyperhalogens as building blocks. We demonstrate this by using Na and Li as metal atoms and F, BF(4), and Na(BF(4))(2) as halogen, superhalogen, and hyperhalogen building blocks. The predicted electron affinities of Na[Na(BF(4))(2)](2) and Li[Li(BF(4))(2)](2) are 9.18 and 9.01 eV, which are, respectively, 0.85 and 0.5 eV higher than those of their hyperhalogen [Na(BF(4))(2) and Li(BF(4))(2)] counterparts.

16.
J Phys Chem A ; 115(36): 10237-43, 2011 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-21834516

RESUMO

Using density functional theory (DFT), we have systematically calculated the equilibrium geometries, electronic structure, and electron detachment energies of Al(BH(4))(n=1→4) and Al(BF(4))(n=1→4) at the B3LYP/6-311+G(2d,p) level of theory. The electron affinities of Al(BH(4))(n) not only exhibit odd-even alternation, just as seen in (BH(4))(n), but also, for n = 3 and 4, show a remarkable behavior: whereas the electron affinities of BH(3) and BH(4) are, respectively, 0.06 and 3.17 eV, those of Al(BH(4))(3) and Al(BH(4))(4) are 0.71 and 5.56 eV. Results where H is replaced by F are also very different. The electron affinities of BF(3) and BF(4) are, respectively, -0.44 and +6.86 eV, and those of Al(BF(4))(3) and Al(BF(4))(4) are 1.82 and 8.86 eV. The results demonstrate not only marked difference when H is replaced by F but also substantially enhanced electron affinities by almost 2 eV when BH(4) and BF(4) units are allowed decorate a metal atom, confirming the recently observed hyperhalogen behavior of superhalogen building blocks.

17.
J Comput Chem ; 32(14): 2974-82, 2011 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-21793005

RESUMO

The electronic and geometrical structures of neutral and negatively charged AlO(5), AlO(6), AlO(7), AlO(8), AlO(9), AlO(10), AlO(11), AlO(12), AlO(15), AlO(16), and AlO(18) along with the corresponding series of ScO(n) and ScO n- oxides were investigated using density functional theory with generalized gradient approximation. We found that these species possess geometrically stable isomers for all values of n = 5-12, 15, 16, 18 and are thermodynamically stable for n = 5-7. The species with n = 16 are found to be octa-dioxides M(η(1)-O(2))(8) while the species with n = 15 and 18 are penta-ozonides (η(2)-O(3))M(η(1)-O(3))(4) and hexa-ozonides M(η(1)-O(3))(6), respectively. Geometrical configurations of a number of the lowest total energy states of Al and Sc oxides are different. Especially, drastic differences are found for the anion AlO n- and ScO n- pairs at n = 9, 10, and 11. The Sc-O bonds are longer than the Al-O bonds by ≈0.2 Å, which, in turn, slightly affects the corresponding interoxygen bond lengths. The charges on metal atoms are close to +2e in both Al series and to +1.5e in both Sc series. As an extra electron is delocalized over ligands in the presence of a large positive charge on the metal atom of the anions, the electron affinity (EA) of the neutrals along with the ionization energies of the anions are large and exceed the EAs of the halogen atoms in a number of cases.

18.
Inorg Chem ; 50(13): 6347-52, 2011 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-21644536

RESUMO

We employed infrared spectroscopy along with complementary lattice dynamics and spin density calculations to investigate pressure-driven local structure distortions in the copper coordination polymer Cu(pyz)F(2)(H(2)O)(2). Here, pyz is pyrazine. Our study reveals rich and fully reversible local lattice distortions that buckle the pyrazine ring, disrupt the bc-plane O-H···F hydrogen-bonding network, and reinforce magnetic property switching. The resiliency of the soft organic ring is a major factor in the stability of this material. Interestingly, the collective character of the lattice vibrations masks direct information on the Cu-N and Cu-O linkages through the series of pressure-induced Jahn-Teller axis switching transitions, although Cu-F bond softening is clearly identified above 3 GPa. These findings illustrate the importance of combined bulk and local probe techniques for microscopic structure determination in complex materials.

19.
J Chem Phys ; 135(24): 244312, 2011 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-22225161

RESUMO

Using a combination of density functional theory and anion photoelectron spectroscopy experiment, we have studied the structure and electronic properties of CuCl(n)(-) (n = 1-5) and Cu(2)Cl(n)(-) (n = 2-5) clusters. Prominent peaks in the mass spectrum of these clusters occurring at n = 2, 3, and 4 in CuCl(n)(-) and at n = 3, 4, and 5 in Cu(2)Cl(n)(-) are shown to be associated with the large electron affinities of their neutral clusters that far exceed the value of Cl. While CuCl(n) (n ≥ 2) clusters are conventional superhalogens with a metal atom at the core surrounded by halogen atoms, Cu(2)Cl(n) (n ≥ 3) clusters are also superhalogens but with (CuCl)(2) forming the core. The good agreement between our calculated and measured electron affinities and vertical detachment energies confirm not only the calculated geometries of these superhalogens but also our interpretation of their electronic structure and relative stability.

20.
J Phys Chem A ; 114(34): 9014-21, 2010 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-20666568

RESUMO

The electronic and geometrical structures of oxygen-rich neutral and negatively charged FeO(5), FeO(6), FeO(7), FeO(8), FeO(9), FeO(10), FeO(11), and FeO(12) clusters were obtained using density functional theory with generalized gradient approximation. With the exception of FeO(11) and FeO(12), all clusters are found to possess a large number of isomers composed of oxo, peroxo, superoxo, and ozonide fragments that are closely spaced in total energy, especially for n = 7 and 8. The preferable structures of FeO(12) are composed of superoxo groups with different orientations. All the neutral species possess rather large electron affinities, which range from 3.24 eV (FeO(8)) to 3.95 eV (FeO(5)). Although all of the lowest energy states were found to possess positive vibrational frequencies and thus are geometrically stable, the states are thermodynamically unstable against dissociation to FeO(4) + (n - 4)/2 O(2) for n = 6, 8, 10, and 12 and FeO(5) + (n - 5)/2 O(2) for n = 7, 9, and 11. In particular, the decay of FeO(12) is exothermic by 34 kcal/mol.


Assuntos
Compostos Férricos/química , Oxigênio/química , Análise Espectral , Modelos Moleculares , Conformação Molecular , Termodinâmica , Vibração
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