Valence Triple-zeta Basis Set Research Articles

An AB Initio Study of the Electronic and Geometric Structure of BIS-of Dipivaloylmethane With Manganese, IRON, and Cobalt

An ab initio study of the structure of Mn(thd)2, Fe(thd)2, and Co(thd)2 complexes in different electronic states is carried out. Quantum chemical calculations are performed using the PC GAMESS program with relativistic effective core pseudopotentials and Gaussian valence triple-zeta basis sets. Calculation methods: DFT/ROB3LYP and CASSCF followed by the inclusion of dynamic electron correlation through multiconfiguration quasi-degenerate second order perturbation theory (MCQDPT2). All three complexes are shown to have a low-spin electronic ground state with a planar structure of the bicyclic fragment at D2h molecular symmetry. The M—O bond is mainly ionic, and M(thd)2 molecules can be considered as an M2+ cation coordinated by two negatively charged bidentate ligands.

Matrix-isolation FT-IR study of (CsBr) n and (CsI) n ( n = 1–3)

The species present in the vapours of CsBr and CsI have been isolated in krypton and xenon matrices and were investigated by FT-IR spectroscopy in the range of 180–30 cm −1. The recorded spectra revealed the presence of substantial amounts of dimer beside the alkali halide monomers. The assignment of the bands and characterization of the fundamentals was carried out on the basis of DFT quantum chemical calculations. The applied B3P86 exchange-correlation functional in conjunction with the Stuttgart–Cologne relativistic effective core potentials and polarized triple-zeta valence basis set reproduced the accurate experimental monomer Cs–Br and Cs–I bond distances within 0.001 Å, and the harmonic stretching frequency within 1.1 cm −1. Based on calculations at this level we report reliable geometrical parameters and fundamental frequencies for the dimer and trimer species (CsBr) n and (CsI) n . Utilizing the computed data we propose the identification of the E′ asymmetric stretching mode of the trimer (CsI) 3 trapped in a Xe matrix and that of (CsBr) 3 in Kr and Xe matrices.

Partially Fluorinated Butatrienes: A Coupled Cluster Study

The geometries of 19 different partially fluorinated butatrienes and their related butenyne isomers have been calculated at the Møller-Plesset second order perturbation theory level with Dunning's valence triple-zeta basis set. Final energies were determined at the CCSD(T)/cc-pVQZ level of theory. Increasing fluorine substitution has only a limited effect on the bond lengths but a substantial effect on the angles. The CCC bond angles of 4 of the 5 partially fluorinated butatrienes show a deviation of more than 2 degrees from collinearity, therefore representing angle-strained butatrienes. Increasing degree of fluorination has a substantial effect on the isomerization energies. The energy difference between the least stable enyne nonfluorinated at the acetylenic center and the most stable enyne fluorinated at the acetylenic center decreases from 66.8 kJ/mol, in case of the monofluorinated system, to 29.7 kJ/mol in the triple fluorinated system. The acetylenic F substitution is crucial in raising the energies of fluorinated but-1-en-3-yne relative to their butatriene isomers. Within the triple fluorinated system and unprecedented for all discussed molecules, 1,1,4-trifluoro-but-1-en-3-yne represents the only molecule fluorinated at the acetylenic center that is more stable than its triene isomer.

Variational determination of the second-order density matrix for the isoelectronic series of beryllium, neon, and silicon

The isoelectronic series of Be, Ne, and Si are investigated using a variational determination of the second-order density matrix. A semidefinite program was developed that exploits all rotational and spin symmetries in the atomic system. We find that the method is capable of describing the strong static electron correlations due to the incipient degeneracy in the hydrogenic spectrum for increasing central charge. Apart from the ground-state energy, various other properties are extracted from the variationally determined second-order density matrix. The ionization energy is constructed using the extended Koopmans' theorem. The natural occupations are also studied, as well as the correlated Hartree-Fock-like single-particle energies. The exploitation of symmetry allows to study the basis set dependence and results are presented for correlation-consistent polarized valence double, triple, and quadruple zeta basis sets.

Quantum dynamics of vibrational excitations and vibrational charge transfer processes in H+ + O2 collisions at collision energy 23 eV

Quantum mechanical study of vibrational state-resolved differential cross sections and transition probabilities for both the elastic/inelastic and the charge transfer processes have been carried out in the H+ + O2 collisions at the experimental collision energy of 23 eV. The quantum dynamics has been performed within the vibrational close-coupling rotational infinite-order sudden approximation framework employing our newly obtained quasi-diabatic potential energy surfaces corresponding to the ground and the first excited electronic states which have been computed using ab initio procedures and Dunning’s correlation consistent-polarized valence triple zeta basis set at the multireference configuration interaction level of accuracy. The present theoretical results for elastic/inelastic processes provide an overall agreement with the available state-selected experimental data, whereas the results for the charge transfer channel show some variance in comparison with those of experiments and are similar to the earlier theoretical results obtained using model effective potential based on projected valence bond method and using semi-empirical diatomics-in-molecules potential. The possible reason for discrepancies and the likely ways to improve the results are discussed in terms of the inclusion of higher excited electronic states into the dynamics calculation.

Full-dimensional ab initio potential energy surface and vibrational configuration interaction calculations for vinyl

The potential energy landscape and two permutationally invariant, full-dimensional ab initio-based potential energy surfaces (PESs) for the doublet vinyl radical, C(2)H(3), are described. The first of the two surfaces, denoted as PES/S, describes the equivalent CH(2)CH global minimum and the saddle point separating them, planar and nonplanar H-atom migration saddle points, a methylcarbyne local minimum that is due to a Jahn-Teller conical intersection, and the saddle point connecting it with the global minimum. The second PES, denoted PES/D, contains all stationary points of PES/S and in addition describes dissociation to C(2)H(2)+H fragments, including the saddle point to dissociation along a least-energy path. The surfaces are least-squares fits to electronic energies obtained with use of the spin-restricted coupled cluster singles and doubles with perturbative treatment of triples method and augmented correlation consistent polarized valence triple zeta basis sets, using permutationally invariant polynomials in "Morse variables" and a many-body expansion. PES/S is a fit to roughly 34,000 and PES/D to roughly 50,000 electronic structure energies. PES/S is used in full-dimensional, vibrational configuration interaction calculations of the vinyl zero-point energy and fundamental vibrational energies, which are compared to recent experiments.

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.

Factorial design analysis of the effects of wave function modifications on calculated HC and CC stretching frequencies in H 2C [dbnd]CHX and HC [tbnd]CX

Two-level factorial designs (FD) have been used to determine the effects of wave function modifications on calculated CH and CC harmonic stretching frequencies of the H 2C CHX and HC CX molecules with X = H, CH 3, F, Cl and CN. These modifications were treated at two levels, which consists in: (I) using either a double- or a triple-zeta valence basis set; (II) including or not diffuse functions in basis set, (III) including or not polarization functions in basis set, and (IV) performing a calculation with or without electron correlation beyond the Hartree–Fock level, i.e., MP2 or B3LYP. Our results have shown that valence (Val), diffuse (Dif), polarization (Pol) and electron correlation (Corr) main effects as well as the Pol/Corr second-order interaction effect are significant to build factorial models for these vibrational modes. When valence and diffuse functions are introduced in the basis set, the calculated HC and CC stretching frequencies are decreased in both the HC CX and H 2C CHX molecules. As expected, by far the correlation principal effect is the most important on the frequency values. This effect provokes a decrease of −281.4 cm −1 and −153.3 cm −1 in the C C and C C vibrational frequencies, respectively, using the MP2 calculations, whereas this decrease for the H C oscillator is −156.1 cm −1 and −116.1 cm −1 in HC CX and H 2C CHX, respectively. This same effect produces an important Pol/Corr interaction effect on HC and CC stretching frequencies, increasing their values by +45.3 cm −1 and +18.4 cm −1 in HC CX, respectively, whereas their corresponding values in H 2C CHX are +43.9 cm −1 and +11.0 cm −1, respectively. Finally, algebraic models were then established to explain how calculated HC and CC stretching frequencies in HC CX and H 2C CHX depend on the characteristics of the molecular orbital wave functions.

Penning ionization electron spectra of pyrene, chrysene, and coronene in collision with metastable He(2 3S) atoms in the gas phase

Penning ionization electron spectra (PIES) of pyrene (C(16)H(10)), chrysene (C(18)H(12)), and coronene (C(24)H(12)) in the gas phase are recorded using metastable He(*)(2 (3)S) atoms. The assignments of PIES are presented based on the outer valence Green's function calculations with the correlation consistent polarized valence triple-zeta basis sets and the exterior electron density calculations of contributing molecular orbitals. The definite positions of all of the pi bands in the PIES are identified making use of the large PIES cross sections. Broad bands are observed in low-electron-energy regions for chrysene and coronene and are ascribed to ionization processes of non-Koopmans types from sigma orbitals. The anisotropic interaction potential energy surfaces for the colliding systems are obtained from ab initio model potentials for the related systems with similar outer valences Li(2 (2)S) + C(16)H(10), C(18)H(12), and C(24)H(12), respectively. The attractive well depths in the out-of-plane directions are found to be similar between these molecules, and the repulsive walls embrace the in-plane perimeters uniformly. Collision energy dependencies for partial Penning ionization cross sections and negative peak shifts in PIES for chrysene support these anisotropic interactions. Effects from thermal populations in low-frequency vibrational modes are estimated to be minor in one-electron ionization processes.

Quantum chemical studies of the adsorption of single acetone molecules on hexagonal ice Ihand cubic ice Ic

The interaction energies of free acetone molecules with surfaces of two different ice polymorphs have been investigated by quantum chemical methods. Special emphasis has been given to sites for adsorption on the (0001) surface of hexagonal ice (I(h)) and the (1[combining macron]01) surface of cubic ice (I(c)), respectively. The structural optimisations made use of conventional electronic structure methods including HF and B3LYP using moderate basis sets up to 6-31+G(d) as well as local and ONIOM methods using 2 or 3 layers which were treated at different levels of theory. The adsorption energies at T = 0 K were calculated for the optimised adsorption geometries performing single points at the B3LYP, MP2 and LMP2 level in conjunction with valence triple-zeta basis sets up to 6-311+G(d,p). Including corrections for basis set superposition errors (BSSE) the most extensive calculations provide adsorption energies (T = 0 K) of -39.1 and -57.5 kJ mol(-1) for the energetically most favourable sites for adsorption of a single acetone molecule on ice I(h) and ice I(c), respectively. By vibrational analysis this can be transformed to adsorption enthalpies at around a temperature of 200 K yielding values of -31.5 for adsorption on ice I(h) and -49.9 kJ mol(-1) for adsorption on ice I(c). The current results support experimental observations of Behr et al. (J. Phys. Chem. A, 2006, 110, 8098) in which evidence was presented that acetone adsorbs on ice around 200 K at two different sites; each of which has a different adsorption enthalpy.

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.

Calculation of the O−H Stretching Vibrational Overtone Spectrum of the Water Dimer

The O-H stretching vibrational overtone spectrum of the water dimer has been calculated with the dimer modeled as two individually vibrating monomer units. Vibrational term values and absorption intensities have been obtained variationally with a computed dipole moment surface and an internal coordinate Hamiltonian, which consists of exact kinetic energy operators within the Born-Oppenheimer approximation of the monomer units. Three-dimensional ab initio potential energy and dipole moment surfaces have been calculated using the internal coordinates of the monomer units using the coupled cluster method including single, double, and perturbative triple excitations [CCSD(T)] with the augmented correlation consistent valence triple zeta basis set (aug-cc-pVTZ). The augmented correlation consistent valence quadruple zeta basis set (aug-cc-pVQZ), counterpoise correction, basis set extrapolation to the complete basis set limit, relativistic corrections, and core and valence electron correlations effects have been included in one-dimensional potential energy surface cuts. The aim is both to investigate the level of ab initio and vibrational calculations necessary to produce accurate results when compared with experiment and to aid the detection of the water dimer under atmospheric conditions.

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).

Ab initio potential energy surfaces and nonadiabatic collision dynamics in H++O2 system

The adiabatic potential energy surfaces for the lowest five electronic states of (3)A" symmetry for the H(+)+O(2) collision system have been obtained at the multireference configuration interaction level of accuracy using Dunning's correlation consistent polarized valence triple zeta basis set. The radial nonadiabatic coupling terms and the mixing angle between the lowest two electronic states (1 (3)A" and 2 (3)A"), which adiabatically correlate in the asymptotic limit to H((2)S)+O(2) (+)(X (2)Pi(g)) and H(+)+O(2)(X (3)Sigma(g)(-)), respectively, have been computed using ab initio procedures at the same level of accuracy to yield the corresponding quasidiabatic potential energy matrix. The computed strengths of the vibrational coupling matrix elements reflect the trend observed for inelastic vibrational excitations of O(2) in the experiments at collision energy of 9.5 eV. The quantum dynamics has been preformed on the newly obtained coupled quasidiabatic potential energy surfaces under the vibrational close-coupling rotational infinite-order sudden framework at the experimental collision energy of 9.5 eV. The present theoretical results for vibrational elastic/inelastic excitations of O(2) are in overall good agreement with the available experimental data obtained from the proton energy-loss spectra in molecular beam experiments [F. A. Gianturco et al., J. Phys. B 14, 667 (1981)]. The results for the complementary charge transfer processes are also presented at this collision energy.

Toward accurate thermochemical models for transition metals: G3Large basis sets for atoms Sc–Zn

An augmented valence triple-zeta basis set, referred to as G3Large, is reported for the first-row transition metal elements Sc through Zn. The basis set is constructed in a manner similar to the G3Large basis set developed previously for other elements (H-Ar, K, Ca, Ga-Kr) and used as a key component in Gaussian-3 theory. It is based on a contraction of a set of 15s13p5d Gaussian primitives to 8s7p3d, and also includes sets of f and g polarization functions, diffuse spd functions, and core df polarization functions. The basis set is evaluated with triples-augmented coupled cluster [CCSD(T)] and Brueckner orbital [BD(T)] methods for a small test set involving energies of atoms, atomic ions, and diatomic hydrides. It performs well for the low-lying s-->d excitation energies of atoms, atomic ionization energies, and the dissociation energies of the diatomic hydrides. The Brueckner orbital-based BD(T) method performs substantially better than Hartree-Fock-based CCSD(T) for molecules such as NiH, where the starting unrestricted Hartree-Fock wavefunction suffers from a high degree of spin contamination. Comparison with available data for geometries of transition metal hydrides also shows good agreement. A smaller basis set without core polarization functions, G3MP2Large, is also defined.

Quantum dynamics of inelastic excitations and charge transfer processes in the H++NO collisions

State-resolved differential cross section, integral cross section, average vibrational energy transfer, and the relative transition probability are computed for the H(+)+NO system using our newly obtained ab initio potential energy surfaces (PES) at the multireference configuration interaction level of accuracy employing the correlation consistent polarized valence triple zeta basis set. The quantum dynamics is treated within the vibrational close-coupling rotational infinite-order sudden approximation using the coupled ground state and first excited state ab initio quasidiabatic PES. The computed collision attributes for the inelastic vibrational excitation are compared with the state-to-state scattering data available at E(c.m.)=9.5 eV and E(c.m.)=29.03 eV and are found to be in overall good agreement with those of the experiments. The results for the vibrational charge transfer processes at these collision energies are also presented.

Ab initio potential energy surfaces and nonadiabatic interactions in the H++NO collision system

Ab initio calculations on the H(+)+NO system have been carried out in Jacobi coordinates at the multireference configuration interaction level employing Dunning's correlation-consistent polarized valence triple zeta basis set to analyze the role of low-lying electronic excited states in influencing the collision dynamics relevant to the experimental collision energy range of 9.5-30 eV. The lowest two adiabatic potential energy surfaces, asymptotically correlating to H(+)+NO(X (2)Pi) and H((2)S)+NO(+)(X (1)Sigma(+)), have been obtained. Using ab initio procedures, the (radial) nonadiabatic couplings and the mixing angle between the lowest two electronic states (1 (2)A' and 2 (2)A') have been obtained to yield the corresponding quasidiabatic potential energy matrix. The strengths of the computed vibrational coupling matrix elements reflect a similar trend, as has been observed experimentally in the magnitudes of the state-to-state transition probability for the inelastic vibrational excitations [J. Krutein and F. Linder, J. Chem. Phys. 71, 559 (1979); F. A. Gianturco et al., J. Phys. B 14, 667 (1981)].

Ab initio characterization of XH3 (X = N,P). Part II. Electric, magnetic and spectroscopic properties of ammonia and phosphine

The coupled cluster theory in conjunction with core valence triple and quadruple zeta basis sets has been employed for investigating electric, magnetic and spectroscopic properties of ammonia and phosphine. Namely molecular dipole and quadrupole moments, NMR shielding and spin-rotation constants, as well as spectroscopic properties such as rotational and centrifugal distortion constants as well as harmonic and anharmonic frequencies of NH3 and PH3 have been determined at a high level of accuracy. To obtain parameters directly comparable to experiment, vibrational effects have also been taken into account. In addition, the basis set convergence has been investigated for the molecular dipole moment.

Calculations of Polarizabilities and Their Gradients for Electron Energy-Loss Spectroscopy

We illustrate for a set of small hydrocarbons, CH4, C2H4, C3H6 and C3H8, the important role of the electric dipole polarizability tensor and its geometric derivatives in theoretical models of electron energy-loss spectra (EELS). The coupled cluster linear response method together with Sadlej's polarized valence triple zeta basis set of atomic orbitals were used to calculate the polarizabilities and polarizability gradients. Incorporation of these ab initio data into the discrete momentum representation method (DMR) leads to perfect agreement between theory and collision experiments.