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1.
J Mol Model ; 19(12): 5579-86, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-24257902

RESUMO

The geometrical structures, energetics properties, and aromaticity of C(36-n) Si(n) (n ≤ 18) fullerene-based clusters were studied using density functional theory calculations. The geometries of C(36-n) Si(n) clusters undergo strong structural deformation with the increase of Si substitution. For the most energy favorable structures of C(36-n) Si(n) , the silicon and carbon atoms form two distinct homogeneous segregations. Subsequently, the binding energy, HOMO-LUMO energy gap, vertical ionization potential, vertical electron affinity, and chemical hardness for the energetic favorable C(36-n) Si(n) geometries were computed and analyzed. In addition, the aromatic property of C(36-n) Si(n) cagelike clusters was investigated, and the result demonstrate that these C(36-n) Si(n) cagelike structures possess strong aromaticity.

2.
J Chem Phys ; 138(7): 074307, 2013 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-23445009

RESUMO

The length modulation of electron transport properties for molecular devices based on fused oligothiophenes has been investigated theoretically using a combination of non-equilibrium Green's functions and first-principles density functional theory. The results show that the lengths of the molecules have a distinct influence on the position of negative differential resistance (NDR) of the molecular devices. By exploring the effect on transmission properties of substituent groups, hexathieno[3,2-b:2',3'-d]thiophene with -NH2 and -NO2 substituents (model L) can be regard as a good candidate of multifunctional molecular device, which shows excellent rectifying performance (the largest rectification ration is 14.3 at 1.2 V) and clear NDR behavior (at 1.4 V).

3.
Phys Chem Chem Phys ; 14(47): 16476-85, 2012 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-23131708

RESUMO

Stimulated by the preparation and characterization of the isolated pentagon rule (IPR) violating chlorofullerene: C(60)Cl(8) (Nat. Mater. 2008, 7, 790-794), we have performed a systematic investigation on the structural stabilities, electronic and optical properties of the IPR-violating C(60)X(8) (X = H, F, and Cl) fullerene compounds via density functional theory. The large energy gaps between the highest occupied and the lowest unoccupied molecular orbitals provide a clear indication of high chemical stabilities of C(60)X(8) derivatives, and moreover, the C(60)X(8) molecules present great aromatic character with the negative nucleus independent chemical shift values. In the addition reactions of C(60) (C(2v)) + 4X(2) → C(60)X(8), a series of exothermic processes are involved, with high reaction energies ranging from -71.97 to -233.16 kcal mol(-1). An investigation on the electronic property shows that C(60)F(8) and C(60)Cl(8) could be excellent electron acceptors as a consequence of large vertical electron affinities. The density of state analysis suggests that the frontier molecular orbitals of C(60)X(8) are mainly from the carbon orbitals of two separate annulene subunits, and the influence from X atoms is secondary. In addition, the ultraviolet-visible spectra and second-order hyperpolarizabilities of C(60)X(8) are calculated by means of time-dependent density functional theory and a finite field approach, respectively. Both the average static linear polarizability <α> and second-order hyperpolarizability <γ> of C(60)X(8) increase greatly compared to those of C(60).

4.
J Comput Chem ; 32(4): 658-67, 2011 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-20845421

RESUMO

Stimulated by the recent isolation and characterization of C56Cl10 chlorofullerene (Tan et al., J Am Chem Soc 2008, 130, 15240), we perform a systematic study on the geometrical structures, thermochemistry, and electronic and optical properties of C56X10 (X = H, F, and Cl) on the basis of density functional theory (DFT). Compared with pristine C56, the equatorial carbon atoms in C56X10 are saturated by X atoms and change to sp³ hybridization to release the large local strains. The addition reactions C56 + 5X2 --> C56X10 are highly exothermic, and the optimal temperature for synthesizing C56X10 should be ranged between 500 and 1000 K. By combining 10 X atoms at the abutting pentagon vertexes and active sites, C56Cl10 molecules exhibit large energy gaps between the highest occupied and lowest unoccupied molecular orbitals (from 2.84 to 3.00 eV), showing high chemical stabilities. The C56F10 and C56Cl10 could be excellent electron acceptors for potential photonic/photovoltaic applications in consequence of their large vertical electron affinities. The density of states is also calculated, which suggest that the frontier molecular orbitals of C56X10 are mainly from the carbon orbitals of two separate annulene subunits, and the contributions derived from X atoms are secondary. In addition, the ultraviolet-visible spectra and second-order hyperpolarizabilities of C56X10 are calculated by means of time-dependent DFT and finite field approach, respectively. Both the average static linear polarizability <α> and second-order hyperpolarizability <γ> of these compounds are larger than those of C60 due to lower symmetric structures and high delocalization of π electron density on the two separate annulene subunits.


Assuntos
Fulerenos/química , Elétrons , Modelos Moleculares , Fenômenos Ópticos , Teoria Quântica , Espectrofotometria
5.
J Comput Chem ; 31(14): 2650-7, 2010 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-20740565

RESUMO

Electronic structures and nonlinear optical properties of two highly deformed halofullerenes C(3v) C(60)F(18) and D(3d) C(60)Cl(30) have been systematically studied by means of density functional theory. The large energy gaps (3.62 and 2.61 eV) between the highest occupied and lowest unoccupied molecular orbitals (HOMOs and LUMOs) and the strong aromatic character (with nucleus-independent chemical shifts varying from -15.08 to -23.71 ppm) of C(60)F(18) and C(60)Cl(30) indicate their high stabilities. Further investigations of electronic property show that C(60)F(18) and C(60)Cl(30) could be excellent electron acceptors for potential photonic/photovoltaic applications in consequence of their large vertical electron affinities. The density of states and frontier molecular orbitals are also calculated, which present that HOMOs and LUMOs are mainly distributed in the tortoise shell subunit of C(60)F(18) and the aromatic [18] trannulene ring of C(60)Cl(30), and the influence from halogen atoms is secondary. In addition, the static linear polarizability and second-order hyperpolarizability of C(60)F(18) and C(60)Cl(30) are calculated using finite-field approach. The values of and for C(60)F(18) and C(60)Cl(30) molecules are significantly larger than those of C(60) because of their lower symmetric structures and high delocalization of pi electrons.


Assuntos
Elétrons , Fulerenos/química , Óptica e Fotônica , Simulação de Dinâmica Molecular , Teoria Quântica
6.
Phys Chem Chem Phys ; 12(36): 10846-56, 2010 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-20657941

RESUMO

Singlet and triplet potential energy surfaces for the reactions of oxygen atoms ((3)P and (1)D) with CF(3)CN have been studied computationally to evaluate the reaction mechanisms, possible products, and rate constants. On the triplet surface, six kinds of pathway are revealed, namely: direct fluorine abstraction, C-addition/elimination, N-addition/elimination, substitution, insertion and F-migration. The results show that the reaction should occur mainly through the C-addition/elimination mechanism involving the chemically activated CF(3)C(O)N* intermediate, and the major products are CF(3) and NCO. The rate constants for C-addition/elimination channel of the reaction of O((3)P) with CF(3)CN have been determined by using RRKM statistical rate theory and compared with the experimental data. On the singlet surface, the atomic oxygen can easily insert into the C-F or C-C bond of CF(3)CN, forming the insertion intermediates FOCF(2)CN and CF(3)OCN, and O((1)D) can add to the carbon or nitrogen atom of the CN group in CF(3)CN, forming the addition intermediates CF(3)C(O)N and CF(3)CNO; both approaches are found to be barrierless. The decomposition and isomerization of some intermediates were also modeled at the QCISD(T)/6-311+G(2df)//B3LYP/6-311+G(d) level for the better understanding of the O((1)D) with CF(3)CN chemistry. The decomposition products CF(3) and NCO arising from CF(3)OCN and CF(3)NCO are the dominant species. Further comparison with similar reactions is also summarized.

7.
J Mol Graph Model ; 28(8): 891-8, 2010 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-20430661

RESUMO

A systematic study on the geometrical structures and electronic properties of C(68)X(4) (X=H, F, and Cl) fullerene compounds has been carried out on the basis of density functional theory. In all classical C(68)X(4) isomers with two adjacent pentagons and one quasifullerene isomer [C(s):C(68)(f)] containing a heptagon in the framework, the C(s):0064 isomers are most favorable in energy. The addition reaction energies of C(68)X(4) (C(s):0064) are high exothermic, and C(68)F(4) is more thermodynamically accessible. The C(68)X(4) (C(s):0064) possess strong aromatic character, with nucleus independent chemical shifts ranging from -22.0 to -26.1 ppm. Further investigations on electronic properties indicate that C(68)F(4) and C(68)Cl(4) could be excellent electron-acceptors for potential photonic/photovoltaic applications in consequence of their large vertical electron affinities (3.29 and 3.15 eV, respectively). The Mulliken charge populations and partial density of states are also calculated, which show that decorating C(68) fullerene with various X atoms will cause remarkably different charge distributions in C(68)X(4) (C(s):0064) and affect their electronic properties distinctly. Finally, the infrared spectra of the most stable C(68)X(4) (C(s):0064) molecules are simulated to assist further experimental characterization.


Assuntos
Fulerenos/química , Modelos Moleculares , Algoritmos , Eletroquímica , Estrutura Molecular , Termodinâmica
8.
J Chem Phys ; 130(12): 124705, 2009 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-19334870

RESUMO

Stimulated by the mass spectroscopic observation of the metallofullerene Ca@C(44), we have performed a systematic investigation to search for the most stable isomer using HF/3-21G approximately LanL2DZ, HF/6-31+G(d), B3LYP/6-31+G(d), and MP2/6-31+G(d)//B3LYP/6-31+G(d) methods. The Ca@C(44) (D(2):53) isomer with eight adjacent pentagons in the fullerene framework is predicted to possess the lowest energy. The thermodynamics stability explorations of Ca@C(44) isomers at different temperatures show that Ca@C(44) (D(2):53) is the most thermodynamically stable in the temperature range of absolute zero to 4000 K. The encapsulation of Ca atom in C(44) fullerene is exothermic, and the electronic structure of Ca@C(44) (D(2):53) can be described formally as Ca(2+)@C(44) (2-). Further analysis on the frontier molecular orbitals and density of states of Ca@C(44) (D(2):53) suggests that both highest occupied molecular orbital and lowest unoccupied molecular orbital are carbonlike with low Ca character, and the carbon cage possesses high chemical activity. In addition, the vibrational spectrum of Ca@C(44) (D(2):53) has been simulated and analyzed to gain an insight into the metal-cage vibrations.

9.
J Comput Chem ; 29(16): 2631-5, 2008 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-18484630

RESUMO

To determine the geometries of the most stable hept-C(62)X(2) (X = F, Cl, and Br) isomers, all 967 possible hept-C(62)F(2) isomers have been orderly optimized using AM1, HF/STO-3G, B3LYP/3-21G, and B3LYP/6-31G* methods, and chlorofullerenes and bromofullerenes, which are isostructural with five most stable hept-C(62)F(2) isomers, were regarded as candidates of the most stable isomer, and optimized at the B3LYP/6-31G* level. The results reveal that 2,9- and 9,62-hept-C(62)X(2) (X = F, Cl, and Br) are the two most stable isomers with slight energy difference. The halogenation releases strain energy of hept-C(62), and all halogenated fullerenes are more chemically stable than hept-C(62) with lower E(HOMO) and higher E(LUMO). All five most stable hept-C(62)X(2) (X = F, Cl, and Br) isomers are energetically favorable, and their thermodynamic stability decreases along with the increase of sizes of addends. Only hept-C(62)F(2) isomers show high thermodynamic stability, and they are potentially synthesized in experiments. 59,62-squ-C(62)X(2) (X = F, Cl, and Br) were computed for comparison, and they are found to be more stable than their heptagon-containing isomers.

10.
J Phys Chem A ; 112(14): 3186-91, 2008 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-18324796

RESUMO

The magnetic-structural correlation in magnetic switchable dinickel(II) complex [LNi2(N3)3] (L- is a pyrazolate-based compartmental ligand) has been investigated on the basis of various unrestricted density functional theory (UDFT) combined with the broken symmetry (BS) approach. The calculated exchange coupling constants were in good agreement with experimental result by using the PBE0 method with LANL2DZ basis set. The antiferromagnetic interaction between the Ni(II) ions is mainly due to the large energy difference of the singly occupied molecular orbitals (SOMOs), and the p orbital overlap for nitrogen atoms on azido and the pyrazolate bridge groups. The analysis of the spin density distribution reveals that both the spin polarization and spin delocalization contribute to the antiferromagnetic interaction. Furthermore, the bistable magnetic behavior for this system (strong antiferromagnetic interaction in low-temperature phase and the week antiferromagnetic in high-temperature phase) results from the change of the Ni-NNN-Ni dihedral angle (tau) in mu1,3-N3. The increase of tau is the key role in decreasing the SOMOs energy difference and weakening the antiferromagnetic interaction. Therefore, the abrupt modulation of the magnitude of M-NNN-M dihedral angle tau in the binuclear-azide complex by external perturbations provides new possibilities for the design of molecular magnetic switching devices.

11.
J Chem Phys ; 124(14): 144108, 2006 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-16626181

RESUMO

An investigation of C(36)X(n) (X=F,Cl,Br; n=2,4,6,12) formed from the initial C(36) fullerene with D(6h) symmetry has been performed using the MP2 theory. Their equilibrium structures, reaction energies, strain energies, lowest unoccupied molecular orbital-highest occupied molecular orbital (LUMO-HOMO) gap energies, and aromaticities have been studied. The calculation results showed that those addition reaction were highly exothermic and C(36)X(n) were more stable than C(36). Moreover, from the view of thermodynamics it should be possible to detect C(36)X(6). The LUMO-HOMO gap energies of C(36)X(n) were higher than D(6h)C(36) and the redox characteristics of C(36)X(n) were weaker comparing to D(6h)C(36). The analyses of pi-orbital axis vector indicated that the chemical reactivity of C(36) was the result of the high strain, and the nucleus independent chemical shifts research showed that the stabilities of the C(36)X(6) were correlative with the conjugation effect.

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