Stable complex C2H4Al4Li3− and its similarity with bicyclo[2.2.0]hex‐2‐ene: A DFT study

We propose that complexation of all metal antiaromatic Al₄Li with C₂H₄ may lead to stable C₂H₄Al₄Li species [II(b)]. Complexation leads to the electron transfer from Al₄Li moiety to C₂H₄ and development of aromatic character in the Al₄ ring. Our proposed compound C₂H₄Al₄Li [II(b)] is very similar to the existing organic compound bicyclo[2.2.0]hex‐2‐ene [I(b)]. The complex C₂H₄Al₄Li [II(b)] can be imagined as an analogue of bicyclo[2.2.0]hex‐2‐ene [I(b)] achieved by a simple replacement of C₄H₄ in the later with π‐isoelectronic Al₄Li moiety in the former. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Aromaticity of ionic structures: Investigation and application of NICS value and 4n + 2 rule

At DFT/B3LYP/6‐31G** theoretical level, C₆H and C (n = 0, ?2, and +2), C₆H and C (n = 0, ±2, ±4, and ±6), C₆H (n = 0–6), as well as C₆H₆‐A and C₆‐A (A = Be, B, N, O, Mg, Al, Si, S, and Fe) structures were investigated. Comparing NICS values of C₆H and C (n = 0, ?2, and +2), we discovered that C₆H, C₆H were antiaromatic, and C₆H₆, C₆, C, C had aromaticity with negative NICS values. According to research of C₆H and C (n = 0, ±2, ±4, ±6), C₆H (n = 0–6), we sustained that their σ and π orbit were different and the locations of electrons were difficult to confirm in ionic structures. Thus, neither 4n + 2 rule nor NICS values can precisely estimate the aromaticity of ionic structures. Besides, through WBI (NBO) research of C₆H₆‐A and C₆‐A (A = Be, B, N, O, Mg, Al, Si, S, and Fe) structures, we found that C₆H₆ was easy to accept electrons, contrarily, C₆ was prone to bestowing electrons. Moreover, C₆H₆ took the symmetrical carbon atoms form feeble interaction or bond, and C₆ used all carbon atoms to impact with other atom. C₆H₆ generated two contrapuntal single bonds with oxygen, sulfur, and nitrogen atoms, whereas C₆ molecule formed double bond with oxygen and nitrogen atoms, two conjoint single bonds with sulfur atom. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Structure and dissociation energy of weakly bound H (n = 5−8) complexes

The geometrical parameters, vibrational frequencies, and dissociation energies for H (n = 5–8) clusters have been investigated using high level ab initio quantum mechanical techniques with large basis sets. The highest level of theory employed in this study is TZ2P CCSD(T). The C₁ structure of H is predicted to be a global minimum, while the C_s structure of H is calculated to be a transition state. Harmonic vibrational frequencies are also determined at the DZP and TZ2P CCSD levels of theory. The dissociation energies, D_e, for H (n = 5–8) have been predicted using energy differences at each optimized geometry, and zero‐point vibrational energies (ZPVEs) are considered to compare with experimental values. The dissociation energies (D_o) have been predicted to be 1.69, 1.65, 1.65, and 1.46 kcal · mol for H, H, H (C₁ symmetry) and H, respectively, at the TZ2P CCSD(T) level of theory. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Dipole,quadrupole, octupole,and dipole–octupole polarizabilities at real and imaginary frequencies for H,HE, and H2 and the dispersion-energy coefficients for interactions between them

We have calculated certain dynamic polarizabilities (for both real and imaginary frequencies) for H, He, and H₂ and the dispersion-energy coefficients for long-range interactions between them. We have done so in a sum-over-states formalism with explicitly electron-correlated wave functions to describe the states. To be precise, we have determined the dipole (α₁), quadrupole (α₂), and octupole (α₃) polarizabilities of H and He for real frequencies (ω) in a range between zero and the first electronic-transition frequency and for imaginary frequencies (iω) on a 32-point Gauss-Legendre grid running from zero to ?ω = 20 E_h, and for H₂, we have found the dipole (α), quadrupole (C), and dipole–octupole (E) polarizability tensors for the same real and imaginary frequencies. The dispersion-energy coefficients, obtained by combining the sum-over-states for-malism for the polarizabilities with analytic integration over ω, gave values of C₆, C₈, and C₁₀ for the atom–atom systems; C, C, C, C, and C for the atom–diatom systems; and C₆, C and C for the H₂? H₂ system. Nearly all the results are considered to be more reliable than those hitherto published and some have been obtained for the first time, e.g., C(iω), E(ω), and E(iω) for H₂ and C, C, and C for the H? H₂ system. © 1993 John Wiley & Sons, Inc.     

Theoretical study of one‐electron bonds in a series of high‐spin lithium–beryllium–hydrogen clusters: “Valence shell single‐electron repulsion” rule and electron localization function analysis

A series of high‐spin clusters containing Li, H, and Be in which the valence shell molecular orbitals (MOs) are occupied by a single electron has been characterized using ab initio and density functional theory (DFT) calculations. A first type (⁵Li₂, ⁿ⁺¹LiH_n+ (n = 2–5), ⁸Li₂H) possesses only one electron pair in the lowest MO, with bond energies of ～3 kcal/mol. In a second type, all the MOs are singly occupied, which results in highly excited species that nevertheless constitute a marked minimum on their potential energy surface (PES). Thus, it is possible to design a larger panel of structures (⁸LiBe, ⁷Li₂, ⁸Li, ⁴LiH⁺, ⁶BeH, ⁿ⁺³LiH (n = 3, 4), ⁿ⁺²LiH (n = 4–6), ⁸Li₂H, ⁹Li₂H, ²²Li₃Be₃ and ²²Li₆H), single‐electron equivalent to doublet “classical” molecules ranging from CO to C₆H₆. The geometrical structure is studied in relation to the valence shell single‐electron repulsion (VSEPR) theory and the electron localization function (ELF) is analyzed, revealing a striking similarity with the corresponding structure having paired electrons. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

The adsorption of CO2, H2CO3, HCO3− and CO32− on Cu2O (111) surface: First‐principles study

The adsorption of CO₂, and its derivatives, H₂CO₃, HCO, and CO, on Cu₂O (111) surface has been investigated by first‐principles calculations based on the density functional theory at B3LYP hybrid functional level. The Cu₂O (111) surface has been modeled using an embedded cluster method,in which the quantum clusters plus some ab initio ion model potentials were inserted in an array of point charges. On the surface, H₂CO₃ was dissociated into an H⁺ and an HCO ion. Among the CO₂ species, HCO was the only activated species on the surface. The results suggest that the reduction of CO₂ on Cu₂O (111) surface can start from the form of HCO. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Evaluation of two‐center,three‐ and four‐electron integrals over Slater‐type orbitals in elliptical coordinates

An algorithm for evaluation of two‐center, three‐electron integrals with the correlation factors of the type rr and rrr as well as four‐electron integrals with the correlation factors rrr and rrr in the Slater basis is presented. This problem has been solved here in elliptical coordinates, using the generalized and modified form of the Neumann expansion of the interelectronic distance function r for k ≥ ?1. Some numerical results are also included. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Theoretical study on the gas‐phase reactivity of halogenated alkylperoxyl radicals toward alkenes

The electrophilic additions of hydroperoxyl (HO ${}_{\text{2}}^{\text{⋅}}$), alkylperoxyl (RO ${}_{\text{2}}^{\text{⋅}}$), and halogenated alkylperoxyl radicals to ethylene were studied using the AM1 and PM3 semiempirical MO methods at the SCF/UHF level. Reactantlike transition states were predicted for the title additions. The AM1 activation enthalpies (ΔH ${}_{\text{f}}^{\text{*}}$) were found to be increased in the order HO ${}_{\text{2}}^{\text{⋅}}$<CH₃O ${}_{\text{2}}^{\text{⋅}}$<C₂H₅O ${}_{\text{2}}^{\text{⋅}}$<i‐C₃H₇O ${}_{\text{2}}^{\text{⋅}}$. The reactivity of an alkylperoxyl radical toward ethylene was found to be increased as the degree of halogen substitution on the alkyl group increased. A good correlation was established between ΔH ${}_{\text{f}}^{\text{*}}$ and the Taft polar substituent constants, σ*. The Evans–Polanyi correlation between ΔH ${}_{\text{f}}^{\text{*}}$ and ΔH ${}_{\text{r}}^{\text{°}}$ was justified and the validity of the Hammond postulate was indicated. The calculated results were compared with the available experimental findings. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 273–283, 1999     

Ab initio studies of negative ion-molecule(s) clusters present in the atmosphere. II. OH−(H2O)n for n = 0, 2, 3, 4

Ab initio calculations are performed with 6–31G basis set to study the geometry and binding of the H₃O, H₅O, H₇O, and H₉O complexes. The H₃O complex is also investigated with the 6–31 G* basis set and MP 2 (Moller–Plesset perturbation theory of second order).     

Convergence accelerator approach for the evaluation of some three‐electron integrals containing explicit rij factors

A simplified analysis is presented for the evaluation of the three‐electron one‐center integrals of the form ∫rrrrrred r ₁d r ₂d r ₃, for the cases i, j, k, ≥−2, l=−2, m≥−1, n≥−1. These integrals arise in the calculation of lower bounds for energy levels and certain relativistic corrections to the energy when Hylleraas‐type basis sets are employed. Convergence accelerator techniques are employed to obtain a reasonable number of digits of precision, without excessive CPU requirements. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 93–99, 1999     

Correlated n1,3S states for coulomb three‐body systems

n^1,3S (n = 1 ? 4) states for atomic three‐body systems are studied with the Angular Correlated Configuration Interaction method. A recently proposed angularly correlated basis set is used to construct, simultaneously and with a single diagonalization, ground and excited states wave functions which: (i) satisfy exactly Kato cusp conditions at the two‐body coalescence points; (ii) involve only linear parameters; (iii) show a fast convergency rate for the energy; and (iv) form an orthogonal set. The efficiency of the method is illustrated by the study a variety of three‐body atomic systems [m m m] with two negatively charged light particles, with diverse masses m and m, and a heavy positively charged nucleus m. The calculated ground 1¹S and excited n^1,3S (n = 2 ? 4) state energies are compared with those given in the literature, when available. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

The formation of highly excited H in the reaction H2+(v) + H2 → H + H

A quasiclassical trajectory surface hopping method has been used to study H(v) + H₂ → H + H for v = 0, 3, 7, 10, 13, and 17 with an emphasis on determining the H internal energy and angular momentum distributions for high v. For v = 13 and 17, significant cross sections are found for producing H at energies above its dissociation energy. An average metastable H lifetime of 11.5 ps for v = 13 and 4.7 ps for v = 17 is found, but there is also a much longer lived component to the lifetime distributions that is more important for v = 13 than for v = 17. Some of the longer lived metastables correspond to high angular momentum orbiting states of H, but other sources of metastability are also present.     

Role of angular electron pair correlation in stabilizing C

A pseudo‐potential that was successfully employed in an earlier study by the Compton group is used to describe the binding of a single electron to a C₆₀ molecule to form C. Then, the interaction of a second electron with the C anion is treated in two manners. First, as performed in the earlier Compton study, a mean‐field (i.e., Hartree–Fock) approach is used to estimate the C‐to‐C energy difference for the singlet state of the dianion and, much as in the earlier study, this dianion is predicted to be unstable by ∼0.4 eV. Second, for this same singlet state, a configuration interaction wave function is employed that allows for the angular correlation of the two excess electrons, allowing them to avoid one another by moving on opposite sides of the C₆₀ skeleton. The energy of the dianion is lowered by 0.3 eV when angular correlation is included, suggesting that the singlet dianion is unstable with respect to electron loss by only ∼0.1 eV. A Coulomb barrier (>1 eV high) and angular momentum barriers then combine to trap electrons of singlet C from detaching, thus producing the very long observed lifetimes. In addition, the energy of the lowest triplet state of C is also discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Ab initio calculation of electronic states of the ions H4+ and H5+

Electronic state calculations for the ions H₄⁺ (with symmetries D ₄ and C _2v) and H (with symmetries D ₅ and D _2d) are made using the valence-bond method. All the configurations obtained from the given set of 1s-functions of Slater type are taken into account. Space functions are used throughout the computation (“spin-free quantum chemistry”). Preliminary quasidiagonalization of the secular equation is implemented by the construction of the multiplet eigenfunctions ^2S+1Γ^(α) from the initial variational functions. The results of the calculations are as follows: the ion H is unstable, the ion H is stable with equilibrium nuclear conformation of symmetry D _2d and with the energy of dissociation into H and H₂ near 4 eV.     

Dipole,quadrupole, octupole,and dipole–dipole–quandrupole polarizabilities and second hyperpolarizabilities at real and imaginary frequencies for helium in the 23S state: Dispersion-energy coefficients for interactions between He(23S) and H(12S), He(11S), He(23S), or H2(X1∑g+)

We have determined the dynamic dipole (α₁), quadrupole (α₂), octupole (α₃), and dipole–dipole–quadrupole (B) polarizabilities and the second hyperpolarizability tensor (γ) for the helium atom in its lowest triplet state (2³S). We have done so for both real and imaginary frequencies: in the former case, for a range of frequencies (ω) between zero and the first electronic-transition frequency, and in the latter case for a 32-point Gauss–Legendre grid running from zero to ?ω = 20 E_h. We have also determined the dispersion-energy coefficients C₆, C₈, and C₁₀ for the systems H(1²S)? He(2³S), He(1¹S)? He(2³S), and He(2³S)? He(2³S) and the C, C, C, C, and C coefficients for the interaction He(2³S)? H₂(X¹∑). Our values of the higher-order multipolar polarizabilities and of γ for the 2³S state of helium are, we believe, the first to be published. © 1993 John Wiley & Sons, Inc.     

Structure and stability of B6, B,and B clusters

We investigated various isomers of B₆, B, and B clusters with ab initio [Hartree–Fock (HF), MP2)] and density functional theory (DFT) methods. Ten B₆ isomers, 6 B isomers, and 6 B isomers are determined to be local minima on their potential energy hypersurfaces by the HF, B3LYP, B3PW91, and MP2 methods. Fourteen of these structures are first reported. The most stable neutral B₆ cluster is the capped pentagonal pyramid (C_5v), in agreement with the results reported previously. Hexagon B (C_2h) isomer and fan‐shaped B (C_2v) isomer are found to be the most stable on the cationic and anionic energy hypersurfaces, respectively. Natural bond orbital analysis suggests that there are three‐centered bonds in the most stable B₆ neutral and ionic clusters. The multicentered bonds are responsible for the special stability of the lowest‐energy isomer. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 269–278, 2003     

Theoretical predictions of the structures and electronic spectra of C60NH with comparisons with the isoelectronic molecules C60O and C60CH2

Intermediate neglect of differential overlap (INDO ) calculations were used to study two structures of C₆₀NH: one of C_2ν, geometry with a bridging NH across the bond between two fused six-membered rings in C₆₀ and the other of C_s geometry with a bridging NH across the bond between a five- and a six-membered ring. We calculated the most stable isomer of C₆₀NH to be of C_2ν, symmetry. It was found that the C_2ν isomer has a protonated aziridine structure with a bridging C? C bond length of 0.1520 nm. The electronic spectra of both isomers of C₆₀NH were calculated. Comparisons were made with the isoelectronic molecules C₆₀O and C₆₀CH₂, cases in which the calculated electronic spectra for the most stable isomers C₆₀O (C_2ν) and C₆₀CH₂ (C_2ν) are in good agreement with recent experimental results. © 1995 John Wiley & Sons, Inc.     

Mechanistic investigation of vibrational fine structure in e‐H2 scattering using local complex potential‐based time dependent wave packet approach

The structural features of vibrational excitation cross‐sections in resonant e‐H₂ scattering have been investigated using a time dependent wave packet approach and a local complex potential to describe the ²Σ H anion. An analysis of the partial contributions to the vibrational excitation cross‐sections reveals that all features of the excitation profile result from simple interference between bound vibrational levels of H₂ and H. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

An Ab initio theoretical investigation on the geometrical and electronic structures of BAun−/0 (n = 1–4) clusters

An ab initio theoretical investigation on the geometrical and electronic structures and photoelectron spectroscopies (PES) of BAu_n^?/0 (n = 1–4) auroboranes has been performed in this work. Density functional theory and coupled cluster method (CCSD(T)) calculations indicate that BAu (n = 1–4) clusters with n‐Au terminals possess similar geometrical structures and bonding patterns with the corresponding boron hydrides BH. The PES spectra of BAu (n = 1–4) anions have been simulated computationally to facilitate their future experimental characterizations. In this series, the T_d BAu anion appears to be unique and particularly interesting: it possesses a perfect tetrahedral geometry and has the highest vertical electron detachment energy (VDE = 3.69 eV), largest HOMO‐LUMO gap (ΔE_gap = 3.0 eV), and the highest first excitation energy (E_ex = 2.18 eV). The possibility to use the tetrahedral BAu unit as the building block of Li⁺[BAu₄]^? ion‐pair and other [BAu₄]^?‐containing inorganic solids is discussed. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

The proton affinity and the structure of protonated species of methylsilane

An ab initio LCAO-MO-SCF calculation was made on the proton affinity (PA ) of methylsilane (CH₃SiH₃) by using STO -3G, MIDI -1, and MIDI -1* basis sets. Three types of protonated methylsilane are taken into account, and their geometrical parameters are optimized. The calculated PA of CH₃SiH₃ is 160.5 kcal/mol, which exceeds that of SiH₄ by 11.5 kcal/mol. The protonated species (I) which refers to Si—C bond protonation is shown to be most favorable, and to be a weak σ-complex between CH₄ and SiH. Other two species are also σ-complexes between H₂ molecule and SiH₃CH or CH₃SiH, and similar to CH, SiH, GeH, and C₂H.