Valence Triple-zeta Basis Set Research Articles

Is the bonding cumulenic or polyacetylenic in nonatetraynylidene?

To answer the entitled question, the equilibrium geometry of the linear triplet ground electronic state X∼3Σg- of nonatetraynylidene (1), HC9H, has been theoretically investigated at various levels of theory. The relative energies, optimal geometry parameters, expectation values of S2, rotational constant, spin densities, and harmonic vibrational frequencies with respect to both restricted open-shell Hartree-Fock (ROHF) and unrestricted HF (UHF) at different levels are examined. The methods employed are HF Self-Consistent Field (SCF), Møller-Plesset perturbation level of theory until second-order (MP2), coupled-cluster singles and doubles (CCSD), and CCSD with perturbative triple excitations (CCSD(T)). Correlation consistent polarized valence double and triple zeta (cc-pVXZ; X=D and T) basis sets are used in all calculations and frozen-core approximation is utilized in all post-SCF calculations. Population analysis of the spin densities at CC levels suggest that several valence structures are possible for 1 implying more polyacetylenic character rather than the cumulenic biradical.

The structures and vibrational spectra of the methyl halide dimers. An ab initio study

Four homodimers and six heterodimers of the methyl halides, CH3X (X = F, Cl, Br, I), have been examined by means of ab initio calculations at the second order level of Møller-Plesset perturbation theory and with an augmented correlation-consistent polarized valence triple-zeta basis set. Three families of dimers have been found. All four homodimers optimize as both cyclic doubly hydrogen-bonded CH … X species and as non-hydrogen-bonded van der Waals C … X aggregates. All six heterodimers also optimize with cyclic doubly bonded structures; in addition, three of them are non-hydrogen-bonded with C … X linkages, and the three containing CH3I are singly bonded, with a CH … I interaction. The properties normally regarded as distinguishing features separating red-shifted from blue-shifted hydrogen bond interactions (CH bond length changes, shifts of the CH stretching wavenumbers and infrared CH stretching band intensity ratios) have been determined, and their variations with respect to the structures of the adducts have been rationalized.

The equilibrium geometries of heptatriynylidene, cyclohepta-1,2,3,4-tetraen-6-yne, and heptahexaenylidene

The equilibrium geometries of heptatriynylidene (1), cyclohepta-1,2,3,4-tetraen-6-yne (2), and heptahexaenylidene (3) have been theoretically investigated at various level of theories. The methods employed are Møller–Plesset perturbation level of theory until second-order, coupled-cluster singles and doubles (CCSD), and CCSD with perturbative triple excitations [CCSD(T)]. Correlation consistent polarized valence double and triple zeta (cc-pVXZ; X=D and T) basis sets are used in all calculations, which are compatible with the frozen-core approximation entreated in this study. The relative energies of the ground triplet electronic state (X∼3Σg-) of 1 – the most stable isomer of C7H2 – to the ground singlet electronic states of 2 (X∼1A1) and 3 (X∼1A1) have also been estimated at different levels. With zero-point vibrational energy corrections, 2 and 3 are found to lie ∼12.27 and ∼20.62kcalmol−1, respectively, above 1 at the highest level of theory (CCSD(T)/cc-pVTZ). While 1 and 3 are observed in the laboratory, 2 is a hypothetical molecule hitherto. Since the optimal geometry of 2 suggests the presence of biradical character, the singlet–triplet (X∼1A1–3B1) energy gap for isomer 2 was also calculated at various levels. The ab initio data presented here may be useful for the laboratory detection of 2 and astronomical detection of2and3.

Ab initio adiabatic and quasidiabatic potential energy surfaces of H++ CN system

We present restricted geometry (collinear and perpendicular approaches of proton) ab initio three dimensional potential energy surfaces for H++ CN system. The calculations were performed at the internally contracted multi-reference configuration interaction level of theory using Dunning’s correlation consistent polarized valence triple zeta basis set. Adiabatic and quasidiabatic surfaces have been computed for the ground and the first excited electronic states. Nonadiabatic effects arising from radial coupling have been analyzed in terms of nonadiabatic coupling matrix elements and coupling potentials. We present ab initio three dimensional potential energy surfaces for H+ + CN system. The calculations were performed at the internally contracted multi-reference configuration interaction (icMRCI) level of theory using Dunning’s correlation consistent polarized valence triple zeta (cc-pVTZ) basis set. Adiabatic and quasidiabatic surfaces were computed for ground and first excited electronic states for the collinear and perpendicular approaches of H+. Nonadiabatic effects arising from radial coupling have been analyzed in terms of nonadiabatic coupling matrix elements (NACME) and coupling potentials.

Communication: An accurate full 15 dimensional permutationally invariant potential energy surface for the OH + CH4 → H2O + CH3 reaction.

A globally accurate full-dimensional potential energy surface (PES) for the OH + CH4 → H2O + CH3 reaction is developed using the permutation invariant polynomial-neural network approach based on ∼135,000 points at the level of correlated coupled cluster singles, doubles, and perturbative triples level with the augmented correlation consistent polarized valence triple-zeta basis set. The total root mean square fitting error is only 3.9 meV or 0.09 kcal/mol. This PES is shown to reproduce energies, geometries, and harmonic frequencies of stationary points along the reaction path. Kinetic and dynamical calculations on the PES indicated a good agreement with the available experimental data.

Is the reaction between formic acid and protonated aminomethanol a possible source of glycine precursors in the interstellar medium?

Context. One of the most interesting questions in interstellar chemistry concerns whether we can detect the basic building blocks of proteins in astronomical sources. In ascertaining whether amino acids could be possible interstellar molecules, a crucial point is how they could be synthesized in the interstellar medium.Aims. We do a theoretical study of the ion-molecule reaction involving protonated aminomethanol and formic acid to establish its viability in space. This ion-molecule reaction has been proposed by other authors as a possible way to produce glycine in the interstellar medium.Methods. The relevant stationary points on the potential energy surface of the reaction between protonated aminomethanol and formic acid have been theoretically studied by using ab initio methods. The second-order Moller-Plesset level was employed, in conjunction with the correlation-consistent polarized valence triple-zeta (cc-pVTZ) basis set. In addition, the electronic energies were refined by means of single-point calculations at the CCSD(T) level (coupled cluster single and double excitation model augmented with a non-iterative treatment of triple excitations) on the MP2/cc-pVTZ geometries with the aug-cc-pVTZ basis set.Results. Formation of protonated glycine is an exothermic process; however, the process presents a net activation barrier that makes this reaction unfeasible under interstellar conditions.Conclusions. The reaction of protonated aminomethanol with formic acid does not seem to be a plausible source of interstellar glycine. This particular case is a clear example that a detailed study of the potential energy surface is needed to establish the relevance of a process in the interstellar medium.

Rotational excitation of NCO induced by collision with Helium at low temperatures

We report the cross sections and the transitional rates of the first 11 rotational levels of the NCO induced by collision with He at low temperatures. For this purpose, we have calculated the potential energy surface (PES), i.e transitional structure between the NCO(X1Σ) and He() by using the coupled cluster singles and doubles perturbed by triple excitations (CCSD(T)). The augmented correlation consistent polarized valence triple zeta (AVTZ) basis set to which we have associated the mid-bond functions, between the molecule and the projectile for a better description of the van der Waals interaction, was used. The PES was interpolated by the Legendre polynomials, analytically fitted, then used for the evaluation of the integral state-to-state rotational transitions cross sections in the close-coupling approach. The rate coefficients were subsequently computed for low kinetic temperature (T 150K).

The molecular complexes of boron trifluoride with nitrosyl fluoride and nitrosyl chloride. Ion-pair formation

The electron donor–acceptor complexes formed between boron trifluoride and the nitrosyl halides ONF and ONCl have been studied by means of ab initio molecular orbital theory at the second order level of Møller–Plesset perturbation theory and with Dunning’s augmented correlation-consistent polarized valence triple-zeta basis set. The focus of the calculations was on the structures, interaction energies and vibrational spectra of the complexes. A variety of trial structures were examined, with electron donation occurring from the oxygen, nitrogen and halogen atoms, in an attempt to establish the most favorable site for interaction. In addition, a number of rotational isomers for each adduct were investigated. It was found that, in both cases, the halogen atom was the preferred donor atom. Several of the optimized structures suggested that the formation of ion pairs would lead to stable complexes, and four separate ion-pair structures were included among the possible associated species for each combination of interacting molecules. In those cases the computed spectra were more consistent with those of the NO+ and BF4− or BClF3− ions than of the corresponding neutral components. The relative stabilities of the two families of complexes have been rationalized and some differences between the properties of the ONF and ONCl adducts have been observed and explained.

TABS: A database of molecular structures

A database of minimum energy structures for 1641 molecules is constructed using the B3LYP density functional with an augmented, correlation consistent, polarized, valence triple-zeta basis set. The molecules all contain one or more carbon atoms and may have one or more H, N, O, F, S, Cl, and Br atoms. The molecules contain up to 34 atoms and 246 electrons. The database contains at least 25 molecules representing each of 24 functional categories. The database provides a reasonably large, moderately accurate, balanced, and consistent set of molecular structures that is useful for the study of inter-relationships among properties of molecules of organic, biochemical, and pharmaceutical interest.

The evolution of the structural, vibrational and electronic properties of the cyclic ethers – on ring size. An ab initio study

The molecular structures, vibrational spectra and atomic charges of the alicyclic ethers containing from two to five carbon atoms have been determined by means of ab initio calculations, at the level of second order Møller–Plesset perturbation theory and using Dunning’s augmented correlation-consistent polarized valence triple-zeta basis set. Two isomers of the oxetane, tetrahydrofuran and tetrahydropyran molecules have been identified and their relative energies determined. Structural properties, such as the COC bond angles and the CH bond lengths, are found to increase steadily with increasing ring size and with decreasing ionization energy. The mean CH2 stretching and bending wavenumbers exhibit the reverse behaviour, while the mean wavenumbers of the CH2 wagging and twisting modes follow the same trend as the structural features. The ring mode wavenumbers vary in a less regular way. The charges of the oxygen, α-carbon and axial and equatorial α- and β-hydrogen atoms also do not show systematic dependences on ring size or ionization energy. The trends in the values of these properties have been rationalized.

Synthesis and aggregation behavior of zinc phthalocyanines substituted with bulky naphthoxy and phenylazonaphthoxy groups: An experimental and theoretical study

Zinc (II) phthalocyanines, bearing peripherally β-naphthol and ({1-[(Z or E)-phenylazo]-2-naphthyl}oxy) have been synthesized and characterized. Aggregation properties of these compounds were investigated in different concentration ranges. The molecular orbital properties and ultraviolet–visible spectra of these phthalocyanines were studied using density functional and time-dependent density functional theories. The computed electronic spectra are in good agreement with the experimental data. Moreover, dimerization of these phthalocyanine complexes in solvent (tetrahydrofuran) medium was investigated by counterpoise corrected interaction energy calculations employing dispersion corrected Becke's 1997 hybrid functional with valence triple-zeta basis set. These calculations revealed that aggregation in these complexes are prevented due to the strong solvent–phthalocyanine interactions and this finding was supported by our experiments.

Communication: An accurate global potential energy surface for the OH + CO → H + CO2 reaction using neural networks

We report a new global potential energy surface of the HOCO system based on the F12 correction of unrestricted coupled-cluster with singles doubles and approximative triples using the augmented correlation-consistent polarized valence triple-zeta basis set (UCCSD(T)-F12/AVTZ), fitted by using the neural networks. Quantum dynamics calculations confirmed the satisfactory convergence of surface with respect to the number of data points and fitting process. It is found that the total reaction probabilities and complex-formation probabilities obtained on the present surface differ considerably with those obtained on the potential energy surface recently reported by Li et al. [J. Chem. Phys. 136, 041103 (2012)]. Various comparisons revealed that the present surface is substantially more accurate than that surface, representing the best available potential energy surface for this benchmark complex-forming four-atom system.

An ab initio study of the properties of some lithium-bonded complexes – Comparison with their hydrogen-bonded analogues

Ab initio calculations have been carried out on a series of complexes formed between lithium fluoride, chloride and bromide on the one hand, and ammonia, water, phosphine and hydrogen sulfide on the other. The calculations were performed using the Gaussian-09 program, at the second order level of Møller–Plesset perturbation theory and with Dunning’s augmented correlation-consistent polarized valence triple-zeta basis set. The properties studied were the molecular structures, interaction energies and vibrational spectra. The results have been compared with those for an analogous set of complexes formed between the three acids hydrogen fluoride, chloride and bromide, and the same four Lewis bases. Common features between the properties of both sets of complexes have been highlighted, and the differences rationalized.

Structure and energetics of small iron clusters

Electronic properties of Fe(2-10) clusters and their ions are described by an all-electron ab initio density functional theory computational analysis using the Handy's OPTX exchange and the gradient-corrected correlation functional of Perdew, Burke and Ernzerhof with a triple-zeta valence basis set plus polarization functions. Ground state structures, magnetic moments, dissociation energies, binding energies, IR vibrational spectra, vertical and adiabatic ionization energies, and electron affinities are reported. Two possible states for Fe(2) which are separated by 81.54 meV are described as possible Fe(2), while the septet (ground state) yields an accurate bond distance (error of 0.02Å); the nonet yields a precise vibrational frequency (error of 10.1cm(-1)). Fe(2) binding energy (0.05 eV/atom error) more closely resembles experimental data than any other previously reported computational methods. In addition, the Fe(6) is found to be the most stable cluster within our set being analyzed.

Ab initio studies of the properties of some halogen-bonded complexes of ammonia, water, phosphine and hydrogen sulphide

Ab initio calculations, at the second order level of Møller–Plesset perturbation theory and with Dunning’s augmented correlation-consistent polarised valence triple-zeta basis set, have been carried out on two series of molecular complexes. One set consists of the common bases ammonia, water, phosphine and hydrogen sulphide and the electron-acceptor halogens difluorine, dichlorine and dibromine, and the other comprises the interhalogens bromine fluoride, chlorine fluoride and bromine chloride as electron acceptors, with the same set of four bases. The interaction energies, molecular structures, vibrational spectra and charge distribution properties of the complexes have been computed, and the adducts have been characterised as halogen-bonded complexes. The trends in the values of these properties correlate with systematic changes in the base and the halogen species. The computed physical data are in quite good agreement with such experimental results as are available, while the anomalous features of some of the properties of the complexes with phosphine have been rationalised.

Theoretical study of spectroscopy, interaction, and dissociation of linear and T-shaped isomers of RgClF (Rg = He, Ne, and Ar) van der Waals complexes

Spectroscopy, interaction energy, and dissociation of linear and T-shaped isomers of HeClF, NeClF, and ArClF van der Waals complexes in their ground state have been studied in detail using MP2 and CCSD(T) methods in conjunction with correlation consistent valence triple and quadruple zeta basis sets. A method, called potential method, has been developed to remove the discrepancy between theoretical and experimental values for the depth of the potential well and dissociation energies for these complexes. This is also supported by the supermolecular approach. Most of the structural and spectroscopic properties of these complexes are first reported and the rest agree very well with the experimental and theoretical values wherever available. Two local minima corresponding to linear and asymmetric T-shaped are found for RgClF complexes. For NeClF complex, the predicted values for the equilibrium bond length and well depth are R NeCl = 3.096 A and $$ D_{\text{e}}^{\text{p}} $$ = 161.50 cm−1 for the linear isomer and R NeCl = 3.503 A and $$ D_{\text{e}}^{\text{p}} $$ = 126.10 cm−1 for the T-shaped isomer. Various dissociation channels are also investigated in detail.

New vibrational assignments for the ν 1 to ν 17 vibrational modes of aziridine and first analysis of the high-resolution infrared spectrum of aziridine between 720 and 1050 cm−1

Fourier transform spectra of aziridine (C2H4NH) were recorded at high resolution (0.002 or 0.003 cm−1) in the 600–1750 and 1750–4000 cm−1 regions, using a Bruker IFS125HR (an upgraded version of the IFS120HR) spectrometer, located at the LISA facility in Creteil. In parallel, the harmonic force field of aziridine was evaluated analytically at the optimized geometry with second-order Møller–Plesset perturbation theory (MP2) together with the correlation-consistent polarized valence triple zeta basis sets cc-pVTZ. These ab initio predictions were used to perform consistent vibrational assignments for the ν 1 to ν 17 fundamental bands of aziridine observed in the infrared spectra recorded during this study. Finally, a first detailed rotational assignment was performed for two B-type bands located at 772.3571 cm−1 (ν 10, CH2 rock) and 997.1592 cm−1 (ν 8, NH bend) and for an A-type band located at 904.0429 cm−1 (ν 17, ring deform). We noticed that the ν 10 band is weakly perturbed, presumably because the v 10 = 1 rotational levels are coupled with those of the v 18 = 1 dark band located around 817 cm−1 through B-type and C-type Coriolis resonances.

On the influence of basis sets and quantum chemical methods on the prediction accuracy of COSMO-RS

This paper examines how the accuracy of activity coefficients at infinite dilution calculated from the conductor-like screening model for real solvents (COSMO-RS) depends on the basis set and the quantum chemical method used. Activity coefficients at various temperatures serve as experimental parameters for optimising the COSMO-RS parameters. A modification of the electrostatic misfit term of the energy function of COSMO-RS is presented that leads to a slightly higher accuracy. COSMO-RS parameter sets for nine different systematically varied basis sets using the density functional theory with the BP86 functional show that at least a valence double-zeta basis set is necessary for good accuracy. Larger basis sets show no advantages. Investigations of eight different quantum chemical calculation methods using a valence triple-zeta basis set are documented. Hartree-Fock and local density approximations give relatively poor results. The gradient-corrected density functionals investigated and the B3LYP hybrid functional show practically identical accuracy. The most accurate parameterisation was obtained with MP2.

Theoretical Study of Alkali Metal Complexes of Porphyrin (М2Р), Porphyrazine (М2Рz) and Phthalocyanine (М2Рc), М=Li, Na, K

The information about geometrical and electronic structure of free molecules M 2 Pz, Na 2 Pc, K 2 Pc is not available. The data concerning structure of Li 2 P complex are not definite. The electronic spectra of M 2 P, M 2 Pz, Na 2 Pc and K 2 Pc are not reported. Here the systematic study of the electronic and geometrical structures of M 2 P, M 2 Pz and M 2 Pc complexes is performed. Density functional theory (three-parameter hybrid functional B3LYP), MollerPlesset perturbation theory (MP2) and correlation-consisted valence triple-zeta basis sets (cc-pvtz) are used. All calculations are carried out using PC GAMESS program. For all molecules several geometrical configurations with different positions of alkali atoms relatively the macrocycle plane are optimized. The structures with alkali atoms adjacent to the same side of the macrocycle (C 2v symmetry) and with alkali atoms lying inside of the macrocycle (D 2h ) correspond to saddle points on PES and possess high relative energies (>150 kJ/mol). More energetically favourable configuration of all complexes excepting Li 2 P possesses D 4h symmetry with alkali atoms taking up symmetrical positions at different sides of the macrocycle. According to B3LYP method the equilibrium structure of Li 2 P is the C 2h geometry originating from distorted D 4h configuration. However MP2 calculation leads to the conclusion about D 4h symmetry of equilibrium structure. Perhaps more sophisticated calculations are needed to determine shape equilibrium configuration in the case of Li 2 P. Analysis of all trends is performed for D 4h configuration and is based on the data obtained at B3LYP level. The geometrical parameters of the macrocycle change systematically in the line Li 2 L → Na 2 L → K 2 L (L=P, Pz, Pc): R e (N-C α ) and ϕ e (C α NC α ) increase by ~0.01 A and ~2o, respectively; R e (C α C β ) decreases by ~0.01 A. R e (C α -X m ) value and the macrocycle cavity size (R e (N⋅⋅⋅N)) increase by 0.011÷0.016 A and 0.11÷0.15 A, respectively. R e (Li-Li) does not change practically in the row Li 2 P → Li 2 Pz → Li 2 Pc (increasing 0.006A). Unlike the R e (Li-Li) trend the magnitudes of R e (Na-Na) and R e (K-K) distances in the similar rows increase by 0.134 and 0.249 A. Perhaps, so different trends can be explained by decreasing of the macrocycle cavity size in M 2 P → M 2 Pc → M 2 Pz line and increasing of the alkali atom radius. Natural net charges on the alkali atoms in all studied compounds are situated in the small range 0.90 ÷ 0.96 ē. Extra negative charge (~2ē) of the macrocycle is located on four pyrrol cycles in M 2 P complexes or on four nitrogen meso-atoms in M 2 Pc and M 2 Pz complexes. According to NBO analysis the bond orders of M-M and М-N are close to zero. Thus the М-N bond is ionic bond. The

Ab initiopotentials ofF+Li2accessible at ultracold temperatures

Ab initio calculations for the strongly exoergic ${\mathrm{Li}}_{2}+\mathrm{F}$ harpoon reaction are presented using density-functional theory, complete active space self-consistent field, and multireference configuration interaction methods to argue that this reaction would be an ideal candidate for investigation with ultracold molecules. The lowest six states are calculated with the aug-correlation-consistent polarized valence triple-zeta basis set and at least two can be accessed by a ground rovibronic ${\mathrm{Li}}_{2}$ molecule with zero collision energy at all reaction geometries. The large reactive cross section (characteristic of harpoon reactions) and chemiluminescent products are additional attractive features of these reactions.