Gallium phosphides GAmPn (m + n = 2–5) and their anions: Structures,electron affinities,and vibrational frequencies

Geometries, electronic states, and electron affinities of Ga_mP_n and Ga_mP (m + n = 2–5) clusters have been examined using four hybrid and pure density functional theory (DFT) methods. Structural optimization and frequency analyses are performed with the basis of a 6‐311+G(2df) one‐particle basis set. The geometries are fully optimized with each DFT method independently. Three types of energy separations reported in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The calculation results show that the singlet structures have higher symmetry than that of doublet structures. The best method for predicting molecular structures was found to be BLYP, while other methods generally underestimated bond lengths. The most reliable adiabatic electron affinities and vertical detachment energy, obtained at the BP86 and B3LYP level of theory, are predicted to be 2.22 and 2.10 eV (GaP), 2.51 and 2.46 eV (Ga₂P), 1.86 and 1.94 eV (GaP₂), 1.96 and 2.27 eV (GaP₃), 1.76 and 1.99 eV (Ga₃P), 1.79 and 2.14 eV (Ga₂P₂), 2.85 and 3.67 eV (GaP₄), 2.08 and 2.10 eV (Ga₄P), 2.90 and 3.17 eV (Ga₂P₃), and 2.70 and 3.37 eV (Ga₃P₂), respectively. Those for Ga₂P, Ga₃P, Ga₂P₂, Ga₄P, GaP₄, Ga₂P₃, and Ga₃P₂ are in good agreement with experiment, but the predicted EA_ad values for GaP, Ga₂P, GaP₂, and GaP₃ are larger than the available experimental values. For the vibrational frequencies of the Ga_mP_n series, the B3LYP method produces good predictions with the average error only ～10 cm^?1 from available experimental and theoretical values. The other three methods overestimate or underestimate the vibrational frequencies, with the worst predictions given by the BLYP method. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Formation of color centers and paramagnetic species upon reduction of poly(diphenylene phthalide) with metallic lithium in DMF

Reduction of poly(diphenylene phthalide) (PDP) with metallic lithium in DMF at room temperature was studied by electronic and ESR spectroscopies. The main feature of the process is the presence of a long induction period (about 50 to 80 min) which is probably caused by the formation of small lithium particles and by adsorption of the polymer on the metal. At least four types of nonparamagnetic color centers characterized by overlapping absorption bands at 570, 660, 750, and 810 nm were detected in the reduced solution. The amounts of all types of the color centers in the solution show a complex dynamic behavior. Reduction of the polymer in the bulk of the solution is due to lithium colloid particles which give rise to a narrow asymmetric ESR singlet (g = 2.0023, ΔH = 0.03 mT, A/B ≈ 1.1–1.8) and absorb light in the region λ ～300–400 nm. Paramagnetic species with quartet ESR signal with a splitting of 0.1 mT and g = 2.0045 observed in the solutions being reduced at a polymer concentration of 0.2 mol L^?1 were attributed to radical anions of terminal anthraquinone groups (TAGs). The electron affinities of some molecules simulating the phthalide-containing unit of the polymer backbone, TAG, and a defect anthrone group were calculated in the B3LYP/6-311+G(d,p) approximation. For diphenylphthalide, the vertical electron affinity EA_vert = 0.21 eV, the adiabatic electron affinity EA_ad = 0.66 eV, the effective electron affinity EA_eff (with allowance for cleavage of C-O bond in the phthalide ring) = 1.23 eV. For anthrone group, one has EA_ad ～1.2 eV and for anthraquinone group, EA_ad ～2 eV. The electron affinities of the model compounds were also calculated with inclusion of the energy of solvation in two solvents (DMF and DMSO) and the energy of polarization in the PDP film. The electronic spectra of some compounds chosen as models for the expected products of reduction (anions and dianions) of the main phthalide-containing fragments in the polymer, TAGs, and defect anthrone groups were also calculated by the TD DFT B3LYP/6-311G(d,p) method. The presence of three types of chemical electron traps and the possibility of manifestation of strong absorption bands of these anions and dianions in the spectral region 500–900 nm precludes unambiguous selection and assignment of complex experimental electronic spectra observed in the course of PDP reduction. The possible role of TAGs in the electronic and photophysical processes in PDP is discussed.     

Structure and properties of iron oxide clusters: From Fe6 to Fe6O20 and from Fe7 to Fe7O24

Geometrical and electronic structures of the neutral and singly negatively charged Fe₆O_n and Fe₇O_m clusters in the range of 1 ≤ n ≤ 20 and 1 ≤ m ≤ 24, respectively, are computed using density functional theory with the generalized gradient approximation. The largest clusters in the two series, Fe₆O₂₀ and Fe₇O₂₄, can be described as Fe(FeO₄)₅ and Fe(FeO₄)₆ or alternatively as [FeO₅](FeO₃)₅ and [FeO₆](FeO₃)₆, respectively. The Fe₆O₂₀ and Fe₇O₂₄ clusters possess adiabatic electron affinities (EA_ad) of 5.64 eV and 5.80 eV and can be attributed to the class of hyperhalogens since FeO₄ is an unique closed‐shell superhalogen with the EA_ad of 3.9 eV. The spin character of the lowest total energy states in both series changes from ferromagnetic to ferrimagnetic or antiferromagnetic when the first Fe? O? Fe bridge is formed. Oxidation decreases substantially the polarizability per atom of the initial bare clusters; namely, from 5.98 ų of Fe₆ to 2.47 ų of Fe₆O₂₀ and from 5.67 ų of Fe₇ to 2.38 ų of Fe₇O₂₄. The results of our computations pertaining to the binding energies of O, Fe, O₂, and FeO in the Fe₇O_m series provide an explanation for the experimentally observed abundance of the iron oxide nanoparticles with stoichiometric compositions. © 2016 Wiley Periodicals, Inc.     

Structures, electron affinities, and vibrational frequencies of the mono-, di-substituted SF6 radicals

Optimized molecular structures, electron affinities, and IR-active vibrational frequencies have been predicted using five different hybrid Hartree–Fock/density functional theory (DFT) methods for a series of mono-, di-substituted SF₆ compounds. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated [J.C. Rienstra-Kiracofe, G.S. Tschumper, H.F. Schaefer, S. Nandi, G.B. Ellison, Chem. Rev. 102 (2002) 231]. The equilibrium configurations of the anions and are found to be a zigzag geometry with ²A electronic state. Three different types of the neutral-anion energy separation reported in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The most reliable adiabatic electron affinities of the mono-, di-substituted SF₆ compounds obtained at the KMLYP function are 1.48 eV (SF₆), 3.20 eV (SF₅Cl), 3.49 eV (SF₅Br), 1.59 eV (SF₅CF₃), 3.21 eV (CF₃SF₄Cl), 3.59 eV (CF₃SF₄Br), 1.36 eV (CF₃SF₄CH₃), 2.32 eV (CF₃SF₄CF₃), respectively.     

Dissociative Electron Attachment to Hexachlorobenzene

Gas phase molecules of hexachlorobenzene (C₆Cl₆) were investigated by means of dissociative electron attachment spectroscopy (DEAS). Three channels of molecular negative ions decay have been identified: abstraction of Cl⁻ and Cl₂⁻ as well as electron detachment (τ_a∼250 μs at 343 K). All three channels exhibit temperature dependence. The adiabatic electron affinity estimated using a simple but typically accurate Arrhenius model (EA_a=1.6–1.9 eV) turns out to be much higher than the quantum-chemical predictions (EA_a=0.9–1.0 eV). We discuss the possible reasons behind the observed discrepancy.     

Relationship between reduction potentials and electron affinities of fullerenes and their derivatives

A linear relationship was found between the first reduction potentials (E°_red) and electron affinities (EA) for fullerenes C₆₀ and C₇₀, their hydro- and fluoro-derivatives, and aromatic hydrocarbons: E°_red = –3.04 + 0.81·EA. This equation was used to estimate the unknown values of EA = 2.45 eV for C₆₀H₂, 2.47 eV for C₇₀H₂, –0.15 eV for C₇₀H_36—38, –0.41 eV for C₇₀H_44—46, and E°_red = –1.74—–1.91 V (vs. Fc^0/+) for C₆₀H₁₈.     

Optoelectronic properties of benzotrithiophene isomers: A density functional theory study

Benzotrithiophene (BTT) isomers were investigated using density functional theory (DFT) and time‐dependent DFT (TD‐DFT) with the aim to explore their structures, linear optical properties, vertical and adiabatic ionization potentials (IP_v and IP_a), electron affinities (EA_v and EA_a), and reorganization energies (λ). The computed bond lengths and bond angles at the B3LYP/6–311+G (d, p) level of theory are in good agreement with experimental crystal structures of the known BTTs. These molecules are planar with zero dihedral angle, making them an ideal backbone for high charge mobility. The UV–visible spectra of BTT isomers are in the range 280–360 nm. All BTT isomers have low hole/electron reorganization energies, which is the main characteristic of good hole/electron transporting materials, and these isomers in turn have potential applications in the field of organic materials.     

Lithium–silicon Si n Li (n = 2–10) clusters and their anions: structures, thermochemistry, and electron affinities

The molecular structures, electron affinities, and dissociation energies of neutral Si _n Li (n = 2–10) species and their anions have been studied by the B3LYP and the BPW91 methods in conjunction with a DZP++ basis set. The geometries have been fully optimized with each of the proposed methods. The ground state structure of neutral Si _n Li keeps the corresponding Si _n framework unchanged. For anion, the corresponding Si _n (or ${{\rm Si}_{n}^{-}}$ ) framework changes largely when n ≥ 7. To evaluate the stability of the resulting anions we have calculated the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The dissociating energies of Li from the lowest energy structures of neutral Si _n Li and their anions are calculated to examine relative stabilities.     

Ab initio investigation of 2,2′‐bis(4‐trifluoromethylphenyl)‐5,5′‐bithiazole for the design of efficient organic field‐effect transistors

The initial molecular structure of 2,2′‐bis(4‐trifluoromethylphenyl)‐ 5,5′‐bithiazole has been optimized in the ground state using density functional theory (DFT). The distribution patterns of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have also been evaluated. To shed light on the charge transfer properties, we have calculated the reorganization energy of electron λ_e, the reorganization energy of hole λ_h, adiabatic electron affinity (EA_a), vertical electron affinity (EA_v), adiabatic ionization potential (IP_a), and vertical ionization potential (IP_v) using DFT. Based on the evaluation of hole reorganization energy, λ_h, and electron reorganization energy, λ_e, it has been predicted that 2,2′‐bis(4‐trifluoromethylphenyl)‐5,5′‐bithiazole would be a better electron transport material. Finally, the effect of electric field on the HOMO, LUMO, and HOMO–LUMO gap were observed to check its suitability for the use as a conducting channel in organic field‐effect transistors. © 2015 Wiley Periodicals, Inc.     

Theoretical Studies on Novel Gridspiroarenes: Structures,Noncovalent Interactions and Reorganization Energies

Organic semiconductor materials with low reorganization energy have various applications such as in organic light‐emitting diodes (OLEDs), organic field‐effect transistor (OFETs) and organic solar cells (OSCs). In this work, we have designed a new class of gridspiroarenes (GS‐SFX and GS‐SITF) with #‐shaped structures, which have novel crisscross geometrical structures compared to widely used spirocyclic arenes—SFX and SITF. The structure electronic properties, adiabatic ionization potentials (IP_a), adiabatic electron affinities (EA_a) and reorganization energies (λ) of GS‐SFX and GS‐SITF have been calculated using density functional theory (DFT) method. The calculated HOMO and LUMO spatial distributions suggest that GS‐SFX and GS‐SITF have better transport properties. The noncovalent interaction analysis shows the weak intramolecular interactions between their arms. The results indicate that the reorganization energies of GS‐SFX and GS‐SITF are significantly reduced compared to the dimer structures—DSFX and DSITF. Furthermore, the GS‐SITF1 which is one of the isomers of GS‐SITF exhibits the lowest values for λ(h) (0.067 eV) and λ(e) (0.153 eV). Therefore, we believe the predicted structure, electronic property, and reorganization energy are good indicator for transport materials. This work has systematically studied the effect of gridization, which provides insights to design organic semiconductor materials with excellent charge transport properties.     

Electronic structure of spheroidal metal containing carbon shells: study of the LaC60 and C60 clusters and their ions within the local density approximation

Ionization thresholds and electron affinities have been calculated within the Local Density Approximation (LDA) for the neutral, positively and negatively charged clusters of LaC₆₀ and C₆₀. The evaluated energies are found to be in good agreement with available experimental data. More accurate measurements are however necessary to verify the suggested spheroidal cage structure for these molecules.     

Spectroscopic constants of SiH2, GeH2, SnH2, and their cations and anions from density functional computations

Local (LSD ) and nonlocal (NLSD ) spin density calculations using different exchangecorrelation functionals have been performed to determine equilibrium geometries, harmonic vibrational frequencies (ωe), ionization potentials (IP ), electron affinities (EA ), dipole moments (μ), and singlet-triplet energy gaps (Δ E_ST) of SiH₂, GeH₂, and SnH₂. Geometrical structures as well as vibrational frequencies are in agreement with the available experimental data and compare favorably with the most sophisticated postHartree-Fock computations performed until now. Both computed IPS (9.15 and 9.25 eV for SiH₂ and GeH₂, respectively) and EA of SiH₂ (1.17 eV) compare favorably with experimental data (9.17, 9.21, and 1.2 eV). Accurate values are obtained also for singlet-triplet energy gaps. We report for the first time the electron affinities of all neutral systems and the spectroscopic constants of the cations and anions. © 1995 John Wiley & Sons, Inc.     

The determination of intrinsic reaction coordinates by density functional theory

The first implementation of the intrinsic reaction coordinate (IRC ) method within the density functional theory (DFT ) framework is presented. The implementation has been applied to four different types of chemical reactions represented by the isomerization process, HCN ? HNC (A); the S_N2 process, H^? + CH₄ ? CH₄ + H^? (B); the exchange process, H˙ + HX ? HX + H˙ (X ? F,Cl) (C); and the elimination process, C₂H₅Cl ? C₂H₄ + HCl (D). The present study presents for each process optimized structures and calculated harmonic vibrational frequencies for the reactant(s), the transition state, and the product(s) along with the IRC path connecting the stationary points. The calculations were carried out within the local density approximation (LDA ) as well as the LDA/NL scheme where the LDA energy expression is augmented by Perdew's and Becke's nonlocal (NL ) corrections. The LDA and LDA/NL results are compared with each other as well as the best available ab initio calculations and experimental data. For reaction (D), ab initio calculations based on MP 2 geometries and MP 4SDTQ energies have been added due to the lack of accurate published post-HF calculations on this process. A detailed discussion is provided on the efficiency of the IRC algorithms, the relative accuracy of the DFT and ab initio schemes, as well as the reaction mechanisms of the four reactions. It is concluded that the LDA/NL scheme affords the same accuracy as does the MP 4 method. The post-HF methods seem to overestimate activation energies, whereas the corresponding LDA/NL estimates are too low. The LDA activation energies are even lower than the LDA/NL counterparts. The incorporation of the IRC method into the DFT framework provides a promising and reliable tool for probing the chemical reaction path on the potential energy surfaces, even for large-size systems. IRC calculations by ab initio methods of an accuracy similar to the LDA/NL scheme, such as the MP 4 scheme, are not feasible. © John Wiley & Sons, Inc.     

Study of the structure and stability of compounds PF n,n=1–5, and their anions by the density functional method

The electronic and geometrical structure of phosphorus fluorides PF_n, n = 1–5, and their singly-charged negative ions was calculated using the density functional method. Both the ground and low-lying excited states of the two series were considered. The structural parameters of neutral radicals PF₂, PF₄, and their anions were obtained for the first time. The adiabatic and vertical electron affinities (EA) of the neutral phosphorus fluorides, and the first ionization potentials of the anions were calculated. According to the calculation results, all the phosphorus fluorides have positive EA_ad, except for PF₃, which has an EA of about zero, and requires further investigation. The dissociation energies of both the neutral and negatively charged phosphorus fluorides were calculated through different channels. All the PF_n and PF _n ^– , n = 1–5, are stable in the gaseous phase. The PF^–, PF ₂ ^– , PF ₃ ^– , and PF ₅ ^– anions have excited states which are stable with respect to both the splitting off of an outer electron and to dissociation.Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2219–2232, October, 1992.     

A CSF-based multi-reference coupled pair approximation III. An application to F2, As2 and As+2

Using the newly developed multi-reference coupled pair approximation program code, the adiabatic potential curves of the ground states of F ₂, As ₂ and As ₂ ⁺ were calculated. Computed spectroscopic constants of these molecules were found to be in good agreement with experimental values. The resulting binding energy of As ₂ (3.86 eV) was compared with the experimental value of 3.99 eV [15] and the best multi-reference configuration interaction value (3.58 eV) reported previously by the present authors. The calculated first adiabatic ionization potential of As ₂ (9.67 eV) was found to be in good agreement with the experimental result. Received: 5 July 1997 / Accepted: 27 August 1997     

The structures,thermochemistry, and electron affinities of hydrogenated silicon clusters Si6Hn/Si6H (n = 3–14)

The hydrogenated silicon clusters structures, electron affinities, and dissociation energies of the Si₆H_n/Si₆H (n = 3?14) species have been systematically investigated by means of three density functional theory (DFT) methods. The basis set used in this work is of double‐ζ plus polarization quality with additional diffuse s‐ and p‐type functions, denoted DZP++. The geometries are fully optimized with each DFT method independently. Three different types of energy separations presented in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The first Si? H dissociation energies D_e (Si₆H_n→ Si₆H_n?1+H) for the neutral Si₆H_n and D_e (Si₆H→Si₆H+H) for the anionic Si₆H species have also been reported. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Unimolecular Reaction Mechanism of an Imidazolin‐2‐ylidene: An iPEPICO Study on the Complex Dissociation of an Arduengo‐Type Carbene

The photoionization and dissociative photoionization of Im(iPr)₂, 1,3‐diisopropylimidazolin‐2‐ylidene, was investigated by imaging photoelectron photoion coincidence (iPEPICO) with vacuum ultraviolet (VUV) synchrotron radiation. A lone‐pair electron of the carbene carbon atom is removed upon ionization and the molecular geometry changes significantly. Only 0.5 eV above the adiabatic ionization energy, IE_ad=7.52±0.1 eV, the carbene cation fragments, yielding propene or a methyl radical in parallel dissociation reactions with appearance energies of 8.22 and 8.17 eV, respectively. Both reaction channels appear at almost the same photon energy, suggesting a shared transition state. This is confirmed by calculations, which reveal the rate‐determining step as hydrogen‐atom migration from the isopropyl group to the carbene carbon center forming a resonance‐stabilized imidazolium ion. Above 10.5 eV, analogous sequential dissociation channels open up. The first propene‐loss fragment ion dissociates further and another methyl or propene is abstracted. Again, a resonance‐stabilized imidazolium ion acts as intermediate. The aromaticity of the system is enhanced even in vertical ionization. Indeed, the coincidence technique confirms that a real imidazolium ion is produced by hydrogen transfer over a small barrier. The simple analysis of the breakdown diagram yields all the clues to disentangle the complex dissociative photoionization mechanism of this intermediate‐sized molecule. Photoelectron photoion coincidence is a promising tool to unveil the fragmentation mechanism of larger molecules in mass spectrometry.     

Superalkali Cations with Trivalent Anion MF<Subscript>6</Subscript><Superscript>3−</Superscript> (M = Al,Ga, Sc) as Central Core

A new series of polynuclear cations MF₆Li₄⁺ (M?=?Al, Ga, Sc) have been theoretically investigated based on density functional theory calculations. The regular octahedral MF₆ groups, although maintained their integrity, distorted to some degree upon the introduction of Li ligands. It has been found that the Li ligands prefer to occupy the bridge- or hollow-site of the MF₆ core. According to the MP2 results, the MF₆Li₄⁺ cations have lower vertical electron affinities (EA_vert, 2.618–3.212 eV) than the threshold of 3.89 eV, verifying their superalkali identity. Besides, the MF₆Li₄⁺ configurations with more dispersive Li ligands possess lower EA_vert values. More importantly, large HOMO–LUMO gaps, binding energies per atom (E_b), and positive fragmentation energies ensure the stability of these cations.