Polarized Valence Triple-zeta Basis Set Research Articles

Calculation of dipole polarizability derivatives of adamantane and their use in electron scattering computations

In this paper we present calculations of the static polarizability and its derivatives for the adamantane molecule carried out at the density functional theory level using the B3LYP exchange-correlation functional and Sadlej’s polarized valence triple zeta basis set. It is shown that the polarizability tensor is necessary to correct long-range behavior of DFT functionals used in electron-molecule scattering calculations. The impact of such a long-range correction is demonstrated on elastic and vibrationally inelastic electron collisions with adamantane, a molecule representing a large polyatomic target for electron scattering calculations.

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.

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.

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.

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.

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.

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.

Open-shell molecular electronic states from the parametric two-electron reduced-density-matrix method

The parametric variational two-electron reduced-density-matrix (2-RDM) method, developed from an analysis of positivity (N-representability) constraints on the 2-RDM, is extended to treat both closed- and open-shell molecules in singlet, doublet, and triplet spin states. The parametric 2-RDM method can be viewed as using N-representability conditions to modify the 2-RDM from a configuration interaction singles-doubles wave function to make the energy size extensive while keeping the 2-RDM approximately N-representable [J. Kollmar, Chem. Phys. 125, 084108 (2006); A. E. DePrince and D. A. Mazziotti, Phys. Rev. A 76, 049903 (2007)]. Vertical excitation energies between triplet and singlet states are computed in a polarized valence triple-zeta basis set. In comparison to traditional single-reference wave function methods, the parametric 2-RDM method recovers a larger percentage of the multireference correlation in the singlet excited states, which improves the accuracy of the vertical excitation energies. Furthermore, we show that molecular geometry optimization within the parametric 2-RDM method can be efficiently performed through a Hellmann-Feynman-like relation for the energy gradient with respect to nuclear coordinates. Both the open-shell extension and the energy-gradient relation are applied to computing relative energies and barrier heights for the isomerization reaction HCN(+)<-->HNC(+). The computed 2-RDMs very nearly satisfy well known, necessary N-representability conditions.

The Benzene−Argon Ground-State Intermolecular Potential Energy Surface Revisited

The benzene-Ar ground-state S(0) intermolecular potential energy surface is evaluated using the coupled cluster singles and doubles model including connected triple corrections and the augmented correlation consistent polarized valence triple-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. The surface is characterized by absolute minima of -390.1 cm(-1) where the argon atom is located on the benzene C(6) axis at distances of +/-3.536 A, and has a general shape close to the available ground-state S(0) and the first singlet S(1) and triplet T(1) excited-state surfaces. Using the potential, the intermolecular level structure of the complex is evaluated. The new intermolecular potential energy surface gives very accurate results and improves those previously available.

Molecular Geometries and Harmonic Frequencies from the Parametric Two-Electron Reduced Density Matrix Method with Application to the HCN ↔ HNC Isomerization

Energies, geometries, and harmonic frequencies of the chemical species in the HCN < = > HNC isomerization including the transition state are computed with the parametric variational two-electron reduced density matrix (2-RDM) method. The parametric 2-RDM method parametrizes the 2-RDM with single- and double-excitation coefficients to be both size-consistent and nearly N-representable [DePrince, A. E., III; Mazziotti, D. A. Phys. Rev. A 2007, 73, 042501.]. With the inclusion of the zero-point energies of both species, the energy of HNC relative to HCN in a polarized valence triple-zeta basis set is 14.2 kcal/mol, which agrees with the experimental value of 14.8 +/- 2 kcal/mol. The present calculations provide the first assessment of the method for computing harmonic frequencies from a molecular geometry optimization. Bond lengths, angles, and harmonic frequencies are also computed for HF, CO, and H2O.

Study of the Xe–NH3 van der Waals complex: High-resolution microwave spectra and ab initio calculations

An ab initio potential energy surface of the Xe-NH(3) van der Waals complex was constructed at the coupled cluster level of theory with single, double, and pertubatively included triple excitations. The small-core pseudopotential and augmented correlation-consistent polarized valence quadruple-zeta basis set was used for the Xe atom and Dunning's augmented correlation-consistent polarized valence triple-zeta basis set for the other atoms. The basis sets were supplemented with midbond functions. Rotational spectra of the Xe-NH(3) van der Waals complex were recorded using a pulsed-nozzle Fourier transform microwave spectrometer. Rotational transitions within two internal rotor states, namely, the Sigma0(0) and Pi1(1) (lower) states, were measured and assigned to the Xe-(14)NH(3) and Xe-(15)NH(3) isotopologues. For the deuterated isotopologues, only the Sigma0(0) states were observed. Two inversion components were observed for each state except for the "s" component of the Sigma0(0) state of the Xe-(14)NH(3) and Xe-(15)NH(3) isotopologues, which has a spin statistical weight of zero. Nuclear quadrupole hyperfine structures arising from the (14)N (nuclear spin angular momentum quantum number I=1) and (131)Xe (I=32) nuclei were detected and analyzed. The observed spectra suggest that the Pi1(1) (lower) state has lower energy than the unobserved Sigma1(1) state, in contrast to the case of Ar-NH(3).

Density functional theory and multireference configuration interaction studies on low-lying excited states of TiO2

Using density functional theory at the BPW916-311+G(3df) level, optimized geometries and energies of the lowest singlet, triplet, and quintet A(1), A(2), B(1), B(2)(C(2v)) states of the TiO(2) molecule were obtained. TiO(2) has a (1)A(1) ground state in C(2v) symmetry. Adiabatic excitation energies of the low-lying singlet and triplet states range from 2.1 to 3.0 eV. The (1,3)A(2) states optimize at bond angles of about 140 degrees , lying only 0.06 eV below linear (1,3)Delta(u), whereas (1,3)B(1) and (1,3)B(2), with bond angles of 120 degrees and 96 degrees , respectively, lie 0.3-0.4 eV below the respective (1,3)Pi(u) or (1,3)Delta(u) states. Minima with short O-O distances of approximately 1.46 A, at energies of 4.2 and 4.7 eV, were found for (1)A(1) and (3)A(1). The C(2v) minima of the lowest (1)B(1) and (3)B(1) states are saddle points, suggesting lower-energy structures in C(s) symmetry. The C(2v) quintet states start at energies of 5.7 eV. Multireference configuration interaction (MRCI) methods, employing a polarized valence triple-zeta basis set, lead to similar geometries and energies. MRCI vertical excitation energies up to 4.6 eV and oscillator strengths are given. The calculated excitation energy of 2.2 eV for (1)B(2) agrees well with 2.3 eV from a fluorescence spectrum. The vertical electron detachment energy of TiO(2) (-) is 1.5 eV, in good agreement with 1.6 eV from anion photoelectron spectroscopy. An observed second photoelectron band corresponds to (1)B(2) and/or (3)B(2), but the assignment of a third band could not be verified. Vibrational frequencies, ionization energies, electron affinities, and dissociation energies are given.

Microwave and ab initio studies of the Xe–CH4 van der Waals complex

An ab initio potential-energy surface of the Xe-CH4 van der Waals complex was constructed at the coupled cluster level of theory with single, double, and perturbatively included triple excitations. The recently developed small-core pseudopotential and augmented correlation-consistent polarized valence quadruple-zeta basis set was used for the xenon atom and Dunning's augmented correlation-consistent polarized valence triple-zeta basis set for the other atoms. The basis sets were supplemented with bond functions. Dipole moments were also calculated at various configurations. Rotational spectra of the Xe-CH4 van der Waals complex were recorded using a pulsed-nozzle Fourier transform microwave spectrometer. The isotopomers studied include those of CH4,13CH4,CD4,CH3D, and CHD3 with the five most abundant Xe isotopes. Transitions within three internal rotor states, namely, the j=0,K=0; j=1,K=0; and j=2,K=1 states, were observed and assigned. Nuclear quadrupole hyperfine structures due to the presence of 131Xe(I=3/2) were detected and analyzed. It was found that the j=1,K=0 state is perturbed by a Coriolis interaction with a nearby j=1,K=1 state. For isotopomers containing CH3D and CHD3, the j=2 states are no longer metastable and could not be observed. The spectroscopic results were used to derive structural and dynamical information of the Xe-CH4 complex.

Microwave spectra of the Xe–N2 van der Waals complex: A comparison of experiment and theory

Rotational transitions for the Xe-N2 complex were measured in the frequency region from 4 to 18 GHz using a pulsed-nozzle Fourier-transform microwave spectrometer. Twelve (four) a-type transitions were recorded for the 132Xe-14N2 and 129Xe-14N2 (131Xe-15N)) isotopomers. In addition, the nuclear quadrupole hyperfine structures due to the presence of the 14N (nuclear-spin quantum number I=1) and 131Xe (I=32) nuclei were detected and analyzed. Two ab initio potential-energy surfaces were calculated at the coupled-cluster level of theory with single, double, and pertubatively included triple excitations. Dunning's augmented correlation-consistent polarized valence triple-zeta basis set was used for the nitrogen atoms. For the first surface, a well-tempered basis set with additional polarization functions was used for the Xe atom; for the second surface, a newly developed augmented correlation-consistent polarized valence quintuple-zeta basis set employing small-core relativistic pseudopotentials was used for the Xe atom. The basis sets were supplemented with bond functions for the van der Waals bond. The counterpoise correction was applied to reduce the basis-set superposition error. The resulting two surfaces both have a single minimum at a T-shaped geometry, with well depths of 122.4 and 119.3 cm(-1), respectively. Bound-state energies supported by the potential-energy surface were determined. The quality of the ab initio potential-energy surfaces was evaluated by comparison of the experimental transition frequencies and rotational and centrifugal distortion constants with those derived from the bound-state energies. A scaled potential-energy surface was obtained which has excellent agreement with the experimental data.

Direct ab initio dynamics study on the rate constants and kinetics isotope effects of CH3O+H→CH2O+H2 reaction

We present a direct ab initio dynamics study of thermal rate constants of the hydrogen abstraction reaction of CH(3)O+H-->CH(2)O+H(2). The unrestricted Becke's half-and-half hybrid functional using the Lee-Yang-Parr correlation functional with Dunning's correlation consistent polarized valence double-zeta basis set, the unrestricted quadratic configuration interaction calculation including single and double substitutions with Dunning's correlation consistent polarized valence double-zeta basis set, and the unrestricted quadratic configuration interaction calculation including single and double substitutions with a triples contribution with Dunning's correlation consistent polarized valence triple-zeta basis set methods were employed to optimize the structures and to calculate frequencies for all stationary points. Minimum energy paths were obtained by the unrestricted Becke's half-and-half hybrid functional using the Lee-Yang-Parr correlation functional and the unrestricted quadratic configuration interaction calculation including single and double substitutions with the same Dunning's correlation consistent polarized valence double-zeta basis set levels of theory. No barrier is found at the unrestricted Becke's half-and-half hybrid functional using the Lee-Yang-Parr correlation functional with Dunning's correlation consistent polarized valence double-zeta basis set level of theory in contrast to a small barrier of 1.43 kcal mol(-1) at the unrestricted quadratic configuration interaction calculation including single and double substitutions with Dunning's correlation consistent polarized valence double-zeta basis set level of theory. In particular, the barrier vanishes as the energies along the minimum energy path MEP are refined at the unrestricted quadratic configuration interaction calculation including single and double substitutions with a triples contribution with Dunning's correlation consistent polarized valence triple-zeta basis set level of theory. Smaller barriers of 0.47 and 0.17 kcal mol(-1) were obtained at the unrestricted quadratic configuration interaction calculation including single and double substitutions with a triples contribution with Dunning's correlation consistent polarized valence triple-zeta basis set and the unrestricted quadratic configuration interaction calculation including single and double substitutions with a triples contribution with Dunning's correlation consistent polarized valence triple-zeta basis set based on the geometries at the unrestricted quadratic configuration interaction calculation including single and double substitutions with Dunning's correlation consistent polarized valence triple-zeta basis set levels of theory, respectively. The forward rate constants are evaluated with the canonical variational transition state theory in the temperature range of 300-2500 K. The calculated forward rate constants at the unrestricted quadratic configuration interaction calculation including single and double substitutions with a triples contribution with Dunning's correlation consistent polarized valence triple-zeta basis set based on the geometries at the unrestricted quadratic configuration interaction calculation including single and double substitutions with Dunning's correlation consistent polarized valence double-zeta basis set level of theory are in good agreement with the available experimental data. The kinetic isotope effects are estimated.

Lifetime of Trimethylene Calculated by Variational Unimolecular Rate Theory

The calculation was undertaken to establish an RRKM prediction of the lifetime of trimethylene for comparison to the experimental result of Zewail and co-workers, 120 ± 20 fs. Nine stationary points on the C3H6 potential energy surface were located using 2,2-CASSCF or 4,4-CASSCF and a polarized valence triple-zeta basis set consisting of [4s3p2d] on C and [3s1p] on H. These included two minima and four saddle points associated with trimethylene previously reported by others. Two saddle points associated with propene formation were located, involving direct 1,2-H transfer and 1,3-H transfer to ethylcarbene, which was also optimized. Three intrinsic reaction coordinate paths were computed for cyclization to cyclopropane using 2,2-CASSCF/6-31G*, and microcanonical variational transition states were located with RRKM theory at seven values of the total energy. Under experimental conditions the lifetime is computed to be 118 fs. The match to experiment suggests that variational RRKM theory may be useful for biradicals even on this short time scale.