Valence Triple-zeta Basis Set Research Articles

Collisional excitation of HCNH+ by He and H2: New potential energy surfaces and inelastic rate coefficients.

Protonated molecules have been increasingly detected in the interstellar medium (ISM), and usually astrochemical models fail at reproducing the abundances derived from observational spectra. Rigorous interpretation of the detected interstellar emission lines requires prior calculations of collisional rate coefficients with H2 and He, i.e., the most abundant species in the ISM. In this work, we focus on the excitation of HCNH+ induced by collision with H2 and He. Therefore, we first calculate ab initio potential energy surfaces (PESs) using the explicitly correlated and standard coupled cluster method with single, double, and non-iterative triple excitation in conjunction with the augmented-correlation consistent-polarized valence triple zeta basis set. Both the HCNH+-H2 and HCNH+-He potentials are characterized by deep global minima of 1426.60 and 271.72 cm-1, respectively, and large anisotropies. From these PESs, we derive state-to-state inelastic cross sections for the 16 low-lying rotational energy levels of HCNH+ using the quantum mechanical close-coupling approach. The differences between cross sections due to ortho- and para-H2 impacts turn out to be minor. Using a thermal average of these data, we retrieve downward rate coefficients for kinetic temperatures of up to 100K. As it could be anticipated, differences of up to two orders of magnitude exist between the rate coefficients induced by H2 and He collisions. We expect that our new collision data will help to improve the disagreement between abundances retrieved from observational spectra and astrochemical models.

First-principles evaluation of the second harmonic generation response of reference organic and inorganic crystals.

Using the CRYSTAL17 package at the coupled-perturbed Kohn-Sham (CPKS) level, periodic boundary conditions first-principles calculations are enacted to predict the second harmonic generation second-order nonlinear optical (NLO) susceptibility, χ(2), values of six historical NLO crystals. This selection allowed the comparison between state-of-the-art calculations and experiment. Several computational aspects are tackled to define conditions where the results are converged with respect to the range of lattice summations, to the number of k-points in the first Brillouin zone, to the order of the multipole expansions for evaluating the long-range part of the electrostatic interactions, as well as to the atomic basis set size. A valence triple zeta basis set supplemented with polarization functions has been selected. Then, χ(2) calculations have been performed using a range of exchange-correlation functionals (XCFs). Results show the large impact of the amount of Hartree-Fock (HF) exchange on the amplitude but also on the signon the χ(2) tensor components. To a given extent, these amplitude effects are consistent with results on molecules, but the signreversal effects and the non-monotonic behavior of the χ(2) tensor components as a function of the amount of HF exchange are scarcely found for molecules. Then, using the recommended range-separated hybrid XCFs, the CPKS scheme leads to good agreement with experimental data for potassium dihydrogenophosphate, urea, and χZXX (2) of LiNbO3. The agreement is more questionable for χZZZ (2) of LiNbO3 whereas it remains poor for ammonium dihydrogenophosphate and 2-methyl-4-nitroaniline, with large underestimations by about a factor of 3, opening a path to further fine-tuning of the ranges of inclusion of HF exchange.

Full-dimensional potential energy surface for the photodissociation of HNCO via its S1 band.

A full-dimensional potential energy surface (PES) for the first excited state S1(1A'') of HNCO has been built up by the neural network method based on more than 36 000 ab initio points, which were calculated at the multireference configuration interaction level with Davidson correction using the augmented correlation consistent polarized valence triple zeta basis set. It was found that two minima, namely, trans and cis isomers of HNCO, and another seven stationary points exist on the S1 PES for the two dissociation pathways: HNCO(S1) → H + NCO/NH + CO. Particularly, a new out-of-plane transition state between the two minima was found in this work, thanks to including all the degree of freedoms for this system. The adiabatic excitation energy of the S1(1A'') ← S0(1A') transition and dissociation energies D0(HNCO → H + NCO) and D0((HNCO →NH(a1Δ) + CO) calculated on the PES are in good agreement with experimental results. In addition, based on the newly constructed S1 PES, the percentage of products H + NCO in the photodissociation of HNCO(S1) was obtained by a quasi-classical trajectory method at the photon wavelengths ranging from 190 to 225 nm, which is in reasonably good agreement with earlier theoretical and experimental results. For the dissociation lifetimes of the trajectories, they were calculated to be less than 5 ps, which is also consistent with experimental observations.

Rotational excitation of NS+ by H2 revisited: A new global potential energy surface and rate coefficients.

Due to the lack of specific collisional data, the abundance of NS+ in cold dense interstellar clouds was determined using collisional rate coefficients of CS as a substitute. To better understand the chemistry of sulfur in the interstellar medium, further abundance modeling using the actual NS+ collisional rate coefficients is needed. For this purpose, we have computed the first full 4D potential energy surface of the NS+-H2 van der Waals complex using the explicitly correlated coupled cluster approach with single, double, and non-iterative triple excitation in conjunction with the augmented-correlation consistent-polarized valence triple zeta basis set. The potential energy surface exhibits a global minimum of 848.24 cm-1 for a planar configuration of the complex. The long-range interaction energy, described using multipolar moments, is sensitive to the orientation of H2 up to radial distances of ∼50 a0. From this new interaction potential, we derived excitation cross sections, induced by collision with ortho- and para-H2, for the 15 low-lying rotational levels of NS+ using the quantum mechanical close-coupling approach. By thermally averaging these data, we determined downward rate coefficients for temperatures up to 50K. By comparing them with the previous NS+-H2 data, we demonstrated that reduced dimensional approaches are not suited for this system. In addition, we found that the CS collisional data underestimate our results by up to an order of magnitude. The differences clearly indicate that the abundance of NS+, in cold dense clouds retrieved from observational spectra, must be reassessed using these new collisional rate coefficients.

Collisional excitation of NH by H2: Potential energy surface and scattering calculations.

Collisional data for the excitation of NH by H2 are key to accurately derive the NH abundance in astrophysical media. We present a new four-dimensional potential energy surface (PES) for the NH-H2 van der Waals complex. The ab initio calculations of the PES were carried out using the explicitly correlated partially spin-restricted coupled cluster method with single, double, and perturbative triple excitations [RCCSD(T)-F12a] with the augmented correlation-consistent polarized valence triple zeta basis set. The PES was represented by an angular expansion in terms of coupled spherical harmonics. The global minimum corresponds to the linear structure with a well depth De = 149.10 cm-1. The calculated dissociation energy D0 is found to be 30.55 and 22.11 cm-1 for ortho-H2 and para-H2 complexes, respectively. These results are in agreement with the experimental values. Then, we perform quantum close-coupling calculations of the fine structure resolved excitation cross sections of NH induced by collisions with ortho-H2 and para-H2 for collisional energies up to 500 cm-1. We find strong differences between collisions induced by ortho-H2 and para-H2. Propensity rules are discussed. The cross sections are larger for fine structure conserving transitions than for fine structure changing ones, as predicted by theory. These new results should help in interpreting NH interstellar spectra and better constrain the abundance of NH in interstellar molecular clouds.

Property-optimized Gaussian basis sets for lanthanides

Property-optimized Gaussian basis sets of split-valence, triple-zeta valence, and quadruple-zeta valence quality are developed for the lanthanides Ce-Lu for use with small-core relativistic effective core potentials. They are constructed in a systematic fashion by augmenting def2 orbital basis sets with diffuse basis functions and minimizing negative static isotropic polarizabilities of lanthanide atoms with respect to basis set exponents within the unrestricted Hartree-Fock method. The basis set quality is assessed using a test set of 70 molecules containing the lanthanides in their common oxidation states and f electron occupations. 5d orbital occupation turns out to be the determining factor for the basis set convergence of polarizabilities in lanthanide atoms and the molecular test set. Therefore, two series of property-optimized basis sets are defined. The augmented def2-SVPD, def2-TZVPPD, and def2-QZVPPD basis sets balance the accuracy of polarizabilities across lanthanide oxidation states. The relative errors in atomic and molecular polarizability calculations are ≤8% for augmented split-valence basis sets, ≤ 2.5% for augmented triple-zeta valence basis sets, and ≤1% for augmented quadruple-zeta valence basis sets. In addition, extended def2-TZVPPDD and def2-QZVPPDD are provided for accurate calculations of lanthanide atoms and neutral clusters. The property-optimized basis sets developed in this work are shown to accurately reproduce electronic absorption spectra of a series of LnCp3 '- complexes (Cp' = C5H4SiMe3, Ln = Ce-Nd, Sm) with time-dependent density functional theory.

An accurate 5D potential energy surface for H3O+-H2 interaction.

Modeling of the observational spectra of H3O+ allows for a detailed understanding of the interstellar oxygen chemistry. While its spectroscopy was intensively studied earlier, our knowledge about the collision of H3O+ with the abundant colliders in the interstellar medium is rather limited. In order to treat these collisional excitation processes, it is first necessary to calculate the potential energy surface (PES) of the interacting species. We have computed the five-dimensional rigid-rotor PES of the H3O+-H2 system from the explicitly correlated coupled-cluster theory at the level of singles and doubles with perturbative corrections for triple excitations [CCSD(T)-F12] with the moderate-size augmented correlation-consistent valence triple zeta (aug-cc-pVTZ) basis set. The well depth of the PES is found to be rather large, about 1887.2 cm-1. The ab initio potential was fitted over an angular expansion in order to effectively use it in quantum scattering codes. As a first application, we computed dissociation energies for the different nuclear spin isomers of the H3O+-H2 complex.

Rotational de-excitations of C3H+ (1Σ+) by collision with He: new ab initio potential energy surface and scattering calculations

ABSTRACT Molecular ions play an important role in the astrochemistry of interstellar and circumstellar media. C3H+ has been identified in the interstellar medium recently. A new potential energy surface of the C3H+–He van der Waals complex is computed using the ab initio explicitly correlated coupled cluster with the single, double and perturbative triple excitation [CCSD(T)-F12] method and the augmented correlation consistent polarized valence triple zeta (aug-cc-pVTZ) basis set. The potential presents a well of 174.6 cm−1 in linear geometry towards the H end. Calculations of pure rotational excitation cross-sections of C3H+ by He are carried out using the exact quantum mechanical close-coupling approach. Cross-sections for transitions among the rotational levels of C3H+ are computed for energies up to 600 cm−1. The cross-sections are used to obtain the collisional rate coefficients for temperatures T ≤ 100 K. Along with laboratory experiments, the results obtained in this work may be very useful for astrophysical applications to understand hydrocarbon chemistry.

The structural, vibrational and electronic properties of the triel-bonded complexes of boron trifluoride with some cyclic ethers – An ab initio study

The properties (molecular structures, vibrational spectra and electronic distributions) of the triel-bonded complexes of boron trifluoride with the cyclic ethers oxirane, oxetane, tetrahydrofuran and tetrahydropyran have been computed. The calculations were carried out ab initio using the Gaussian 16 program at the second order level of Møller-Plesset perturbation theory (MP2) and with Dunning’s augmented correlation-consistent polarized valence triple-zeta basis sets (aug-cc-pVTZ). The results indicate that, with the exception of the oxirane complex, the interaction energies, the bond length and angle changes and the perturbations of the BF3 fragment vibrational wavenumbers are remarkably invariant to the ring size of the base. The unique position of the oxirane complex is associated with the extent of ring strain in the monomer relative to those of the other three bases.

An accurate potential energy surface and ring polymer molecular dynamics study of the Cl + CH4 → HCl + CH3 reaction.

The reaction Cl + CH4 → HCl + CH3, a prototypical bimolecular reaction, has been established as an important proving ground for studying chemical reaction kinetics and dynamics of polyatomic molecules. In this work, a globally accurate full-dimensional potential energy surface (PES) for this reaction is developed by using the permutationally invariant polynomial neural network (PIP-NN) approach based on 74 000 points calculated at the level of the explicitly correlated unrestricted coupled cluster single, double, and perturbative triple level with the augmented correlation corrected valence triple-zeta basis set (UCCSD(T)-F12a/AVTZ). For points in the entrance channel, spin-orbit corrections stemming from Cl(2P) are determined at the level of complete active space self-consistent field (CASSCF) with the AVTZ basis set. With this PES, thermal rate coefficients and kinetic isotope effects are computed for reactions Cl + CH4 → HCl + CH3 and Cl + CD4 → DCl + CD3 using the ring polymer molecular dynamics (RPMD) method, which can provide reliable estimations for thermal rate coefficients effectively. Generally, the agreement with the scattered experimental results is reasonably satisfactory.

A Comparison of NH2+5 and CH+5 Ions and Deuterated Variants of NHxD2+(5− x): Real or Artefactual Rotation?

Protonated NH 5 2+ has unusual vibrational and rotational behavior because its three nonequivalent equilibrium structures have nearly identical energies and its five protons scramble freely, while in the CH 5 + structure, five hydrogen atoms are bonded to the carbon atom by sharing eight valence electrons. Although a few theoretical papers have been published on quantum mechanics of those systems. Better understanding requires spectral and conformational analyses. CASSCF (8, 9) calculations with the correlation consistent polarized valence double and triple zeta basis sets are accomplished for estimating the vibrational data and zero-point energies of those two ions. The present results indicate that normal modes agree qualitatively with NHxD (5- ) 2+ and one of the normal modes indicates that NH 5 2+ is highly fluxional and has a complex spectrum while the broken N-H bonds are reformed all the time. The spectrum of mode 10 is highly complex with red and some blue shifts. In particular, modes 6 and 12 are attributed to the rapid coupling of the N-H stretching normal mode to motions more closely related to isomerization, i.e., bending or rocking. There have been long debates whether NH 5 2+ has a structure at all or not and if the rotation is real or artefactual.

A Continuum from Halogen Bonds to Covalent Bonds: Where Do λ3 Iodanes Fit?

The intrinsic bonding nature of λ 3 -iodanes was investigated to determine where its hypervalent bonds fit along the spectrum between halogen bonding and covalent bonding. Density functional theory with an augmented Dunning valence triple zeta basis set ( ω B97X-D/aug-cc-pVTZ) coupled with vibrational spectroscopy was utilized to study a diverse set of 34 hypervalent iodine compounds. This level of theory was rationalized by comparing computational and experimental data for a small set of closely-related and well-studied iodine molecules and by a comparison with CCSD(T)/aug-cc-pVTZ results for a subset of the investigated iodine compounds. Axial bonds in λ 3 -iodanes fit between the three-center four-electron bond, as observed for the trihalide species IF 2 − and the covalent FI molecule. The equatorial bonds in λ 3 -iodanes are of a covalent nature. We explored how the equatorial ligand and axial substituents affect the chemical properties of λ 3 -iodanes by analyzing natural bond orbital charges, local vibrational modes, the covalent/electrostatic character, and the three-center four-electron bonding character. In summary, our results show for the first time that there is a smooth transition between halogen bonding → 3c–4e bonding in trihalides → 3c–4e bonding in hypervalent iodine compounds → covalent bonding, opening a manifold of new avenues for the design of hypervalent iodine compounds with specific properties.

Dissection of the multichannel reaction of acetylene with atomic oxygen: from the global potential energy surface to rate coefficients and branching dynamics.

The O(3P) + C2H2 reaction is the first step in acetylene oxidation. The accurate kinetic data and the understanding of the reaction dynamics is of great importance. To this end, a full-dimensional global potential energy surface (PES) for the ground triplet state of the O(3P) + C2H2 reaction is constructed based on approximately 85 000 ab initio points calculated at the level of explicitly correlated unrestricted coupled cluster single, double, and perturbative triple excitations with the explicitly correlated polarized valence triple zeta basis set (UCCSD(T)-F12b/VTZ-F12). The PES is fit using the permutation invariant polynomial-neural network (PIP-NN) approach with a total root mean square error of 0.21 kcal mol-1. The key topographic features of the PES, including multiple potential wells and saddle points along different reaction pathways, are well represented by this fit PES. The kinetics and dynamics of the O(3P) + C2H2 reaction are investigated using the quasi-classical trajectory (QCT) method. The calculated rate coefficients are in good agreement with experimental data over a wide temperature range, especially when the temperature is lower than 1500 K. The product branch ratio has also been determined, which indicates the H + HCCO channel as the dominant reaction pathway at 298-3000 K, accounting for 80-90% of the overall rate coefficient, in agreement with experimental observations. The dynamics of the reaction is analyzed in detail.

A comparison of NH52+ and CH5+ ions and deuterated variants of NHx D(5–x)2+: Real or artefactual rotation?

Protonated NH52+ has unusual vibrational and rotational behavior because its three nonequivalent equilibrium structures have nearly identical energies and its five protons scramble freely, while in the CH5+ structure, five hydrogens are bonded to the carbon atom by sharing eight valence electrons. Although a few theoretical papers have been published on the quantum mechanics of those systems. Better understanding requires spectral and conformational analysis. CASSCF (8, 9) calculations with the correlation consistent polarized valence double and triple zeta basis sets are accomplished for estimating the vibrational data and zero-point energies of two those ions .The present results indicate the normal modes agree qualitatively with NHxD(5-x)2+ and one of the normal modes indicates that NH52+ is highly fluxional and has a complex spectrum while the broken N—H bonds are reformed all the time. The spectrum of mode 10 is highly complex with red and some blue shifts. In particular, modes 6 and 12 are attributed to the rapid coupling of the N—H stretching normal mode to motions more closely related to isomerization, i.e., bending or rocking. There have been long debates whether NH52+ has a structure at all or not and if the rotation is real or artefactual.

Study of $${\text{CD}}_{5}^{ + }$$ Ions and Deuterated Variants( $${\text{C}}{{{\text{H}}}_{x}}{\text{D}}_{{(5 - x)}}^{ + }$$ ): An Artefactual Rotation

Deuterated methane, $${\text{CD}}_{5}^{ + }$$ , has unusual vibrational and rotational behavior because its three nonequivalent equilibrium structures have nearly identical energies and its five protons scramble freely. Although a few theoretical papers have been published on the quantum mechanics of these systems, a better understanding requires spectral and conformational analysis. Post Hartree-Fock, Moller-Plesset and DFT calculations with the correlation consistent polarized valence double and triple zeta basis sets have been accomplished for estimating the thermodynamic data and zero-point energies of $${\text{C}}{{{\text{H}}}_{x}}{\text{D}}_{{(5 - x)}}^{ + }$$ . The present results indicates the normal modes agree with qualitative of $${\text{C}}{{{\text{H}}}_{x}}{\text{D}}_{{(5 - x)}}^{ + }$$ which modes 10 indicates $${\text{CD}}_{5}^{ + }$$ is highly fluxional and has a complex spectrum while the C–D bonds which are broken and reformed all the time. The spectrum of mode 12 is highly complex with red-and some blue shifts. In particular, modes 8 and 10 be attributed to the rapid coupling of the CD-stretching normal mode to motions more closely related to isomerization, i.e., bending or rocking. There has thus been a long debate whether $${\text{CD}}_{5}^{ + }$$ has a structure at all or not and is it real rotational motions or artefactual.

On symmetry breaking of CH5+ ions and deuterated variants (CHxD (5-x) +): real or artefactual rotational motions?

Protonated methane, CH5 + , has unusual vibrational and rotational behavior because its three nonequivalent equilibrium structures have nearly identical energies and its five protons scramble freely. Although a few theoretical papers have been published on the quantum mechanics of these systems, a better understanding requires spectral and conformational analysis. Post hartree-fock, Moller-Plesset and DFT calculations with the correlation consistent polarized valence double and triple zeta basis sets have been accomplished for estimating the thermodynamic data and zero-point energies of CH x D (5-x) + .The present results indicates the normal modes agree with qualitative of CH x D (5-x) + which modes 10 indicates CH 5 + is highly fluxional and has a complex spectrum while the C-H bonds which are broken and reformed all the time. The spectrum of mode 12 is highly complex with red-and some blue shifts. In particular, modes 8 and 10 be attributed to the rapid coupling of the CH-stretching normal mode to motions more closely related to isomerization, i.e., bending or rocking. There has thus been a long debate whether CH5+ has a structure at all or not and is it real rotational motions or artefactual.

Collisional excitation of interstellar PO(X2Π) by He: new ab initio potential energy surfaces and scattering calculations.

We present the first ab initio potential energy surfaces (PESs) for the PO(X2Π)-He van der Waals system. The PESs were obtained using the open-shell partially spin-restricted coupled cluster approach with single, double and perturbative triple excitations [UCCSD(T)]. The augmented correlation-consistent polarized valence triple-zeta (aug-cc-pVTZ) basis set was employed supplemented by mid-bond functions. Integral and differential cross sections for the rotational excitation in PO-He collisions were calculated using the new PES and compared with results in similar systems. Finally, our work presents the first hyperfine-resolved cross sections for this system that are needed for accurate modelling in astrophysical environments.

Computational study on the molecular conformations of phenolic compounds

The study of the conformation of eight phenolic compounds (i.e. phenol, guaiacol, syringol, pyrocatechol, o-, m-, p-cresol and vanillin) was carried out using B3LYP (Becke, 3-parameter, Lee-Yan-Parr) method and cc-pVTZ (correlation consistent polarized polarisation Valence triple zeta) basis set. Potential energy surfaces were plotted in order to identify the minimum energy structures and the transition states. For the first time, structures of vanillin and syringol were completely determined. Moreover, our work also confirms that the most stable conformations of m-cresol and p-cresol are obtained when the methyl group presents a hydrogen atom at the perpendicular of the benzene ring. The possibility of intramolecular hydrogen bonding was also investigated. Guaiacol, pyrocatechol, syringol and vanillin present a structure stabilized by the presence of a moderate hydrogen bond. Finally, potential energy barriers and rotational potential functions were calculated. The comparison of the rotational potential parameters for each molecule highlights the presence of similarities specific to each substituent and their neighbours.

Ionic species in vapour over barium diiodide: Quantum chemical study of structure and thermodynamic properties

The cluster ions Ba2I3+, Ba3I5+ and Ba4I7+ were detected earlier in saturated vapour over barium diiodide using high temperature mass spectrometric technique. In this work the structure and thermodynamic properties of the species BaI3−, Ba2I3+, Ba3I5+, Ba4I7+, and Ba5I9+ have been studied theoretically by using the density functional theory (DFT/B3P86) and Møller–Plesset perturbation theory (MP2 and MP4) with triple-zeta valence basis sets. The enthalpies of ion molecular reactions have been determined both theoretically and based of available experimental data; the enthalpies of formation of the cluster ions are found as follows (in kJmol−1): −709±6, (BaI3−), −96±10 (Ba2I3+), −654±15 (Ba3I5+), −1177±20 (Ba4I7+) and −1686±20 (Ba5I9+).

Structure and thermodynamic properties of cluster ions in saturated vapour over barium dibromide

The structure and thermodynamic properties of cluster ions detected earlier in saturated vapour over barium dibromide were studied theoretically. The equilibrium geometrical parameters and vibrational spectra were computed for the ions BaBr3−, Ba2Br3+, Ba3Br5+, Ba4Br7+ and Ba5Br9+; the DFT and MP2 methods with triple-zeta valence basis sets were used. The enthalpies of ion molecular reactions were obtained both theoretically through the total energies of participants and based on experimental data. The theoretical results were scrutinized with respect to methods of computation (DFT, MP2, and MP4). The enthalpies of formation ΔfHo(0) of the ions have been determined (in kJmol−1): −858±6 (BaBr3−); −293±10 (Ba2Br3+); −982±20 (Ba3Br5+); −1644±30 (Ba4Br7+); −2282±17 (Ba5Br9+).