Augmented Correlation Consistent Basis Sets Research Articles

Ab initio Study of the Fluoride—Ammonia Clusters: F‐—(NH3)n, n = 1—3

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structures and infrared spectra of fluoride–hydrogen sulfide clusters from ab initio calculations: F–-(H2S)n, n= 1–5

Clusters formed between a fluoride anion and several hydrogen sulfide molecules have been investigated via ab initio calculations at the MP2 level of theory, using Dunning's augmented correlation consistent basis sets. Optimised geometries, vibrational frequencies, and enthalpy changes for the ligand association reactions are presented for clusters with up to five H2S ligands interacting with a F- anion. The minimum energy structure for the 1:1 F(-)-H2S complex features proton transfer from the H2S to the F- anion, forming a planar C(s) symmetry FH...SH- structure. For the F(-)-(H2S)2 cluster, the FH...SH- core remains and is solvated by a perturbed H2S ligand. For the larger F(-)-(H2S)(3-5) clusters, in addition to the FH...SH(-)-(H2S)n cluster forms, other minima featuring a 'solvated F-' anion are predicted. Calculated infrared spectra for the minima of each cluster size are presented to aid in assigning spectra from future experimental studies.

Electron Affinities of BN, NO and NF: Coupled Cluster and Multireference Configuration Interaction Calculations

The accurate adiabatic electron affinities (EA) of the BN, NO and NF molecules have been determined using the coupled cluster approach and multireference configuration interaction methods. By combining large doubly augmented correlation-consistent basis sets (through the sextuple zeta) and complete basis set extrapolations with corrections for core-valence correlation and relativistic effects, we find that the RCCSD(T) method gives EA(BN) = 3.153 eV in very close agreement with experiment and predicts EA(NF) = 0.247 eV. The RCCSD(T) and UCCSD(T) EA(NO) results, 0.008 and 0.031 eV, bracket the experimental value. For both the neutral and anionic ground state species the usual spectroscopic constants were derived.

The molecular electric quadrupole moment and electric-field-gradient induced birefringence (Buckingham effect) of Cl2

An ab initio investigation of the molecular properties rationalizing the electric-field-gradient induced birefringence (Buckingham effect) for Cl$_2$ is presented. The quadrupole moment is determined using hierarchies of basis sets and wavefunction models. The electric dipole polarizability, the dipole - dipole - quadrupole and dipole - dipole - magnetic dipole hyperpolarizabilities are determined exploiting a Coupled Cluster Singles and Doubles (CCSD) response approach. The properties are zero-point vibrationally averaged, and the contribution of excited ro-vibrational states accounted for. To this end, the interatomic $^1$Σ$_g^+$ ground state potential has been computed at CCSD plus perturbative triples - CCSD(T) - level employing a large augmented correlation consistent basis set. The effect of relativity is estimated at the Dirac-Hartree-Fock level. Our best value for the quadrupole moment of Cl$_2$ is (2.327 ± 0.010) au and it is in excellent agreement with experiment which, after revision and dependent on the procedure employed for correcting the original estimate of (2.24 ± 0.04) au of Graham et al., [Mol. Phys., 93, 49, (1998)], ranges from (2.31 ± 0.04) au to (2.36 ± 0.04) au.

Density-functional and electron correlated study of five linear birefringences—Kerr, Cotton–Mouton, Buckingham, Jones, and magnetoelectric—in gaseous benzene

We present the results of an extended study of five birefringences--Kerr, Cotton-Mouton, Buckingham, Jones, and Magnetoelectric--on benzene in the gas phase. The relevant molecular quantities--first-order properties, linear, quadratic, and cubic response functions--are computed employing the density-functional theory (DFT) response theory, with a choice of functionals. In some cases, different functionals are employed for the wave-function computational step and for the subsequent analytical response calculation to determine the combination yielding at the same time the optimal energy and energy derivative results. Augmented correlation consistent basis sets of double and triple zeta quality are used. The DFT results are compared to those obtained at the Hartree-Fock level and in some cases within a coupled cluster singles and doubles electronic structure model. The study tries to assess the ability of the DFT response theory to describe a wide range of properties in a system of rather large size and high complexity. The relative strength of the five birefringences for plausible experimental conditions is determined and, when possible, comparison is made with the results of the measurements.

SO 3 revisited: Impact of tight d augmented correlation consistent basis sets on atomization energy and structure

The atomization energy and structure of SO 3 have been calculated using the advanced ab initio method, CCSD(T), in combination with the newly revised families of correlation consistent basis sets, cc-pV( n + d)Z and aug-cc-pV( n + d)Z (where n = D(2), T(3), Q(4), or 5). The impact of these sets upon structure and energy has been examined, as has convergence behavior toward the complete basis set (CBS) limit. Overall, these revised sets have a particularly strong effect upon energies determined using the lower level basis sets, and can reduce the unusually large deviation from experiment by over half.

Ab initio potential energy surface for HeF2 in its ground electronic state

The ground state potential energy surface for He-F 2 has been generated using the coupled-cluster singles and doubles excitation approach with perturbative treatment of triple excitations [CCSD(T)] and multi-reference configuration interaction (MRCI) methodologies, with augmented correlation consistent quadruple zeta basis set and diffused functions. Both the CCSD(T) and MRCI surfaces are compared and the results analyzed. The CCSD(T) surface exhibits van der Waals minima at different distances for different orientations of He approaching F 2 and is adequate to describe accurately only in the region around the equilibrium bond distance of F 2 . The MRCI surface, on the other hand, yields reliable results for a wider range of F-F bond distances leading to the correct asymptote. Davidson correction to the MRCI surface makes it purely repulsive over the regions investigated.

Three-Dimensional ab Initio Potential and Ground State Dynamics of the HeI2 Complex

The interaction potential for the HeI2 molecule is studied using the coupled-cluster (CCSD(T)) method. A correlation-consistent triple-ζ valence basis set in conjunction with a large-core Stuttgart−Dresden−Bonn (SDB) relativistic pseudopotential is used for the iodine atoms, whereas augmented correlation-consistent basis sets, aug-cc-pV5Z, are used for the He atom, supplemented with a set of bond functions. The potential energy surface of the ground electronic state of HeI2 shows a double-minimum topology, with an isomerization barrier of 25.64 cm-1. Bound state calculations are carried out for J = 0, and the lowest vibrational vdW level corresponds to the linear configuration, while a level found only 0.7 cm-1 above is assigned to a T-shaped isomer. The CCSD(T) dissociation energies for the linear and T-shaped configurations are found to be = 15.38 cm-1 and = 14.68 cm-1, with vibrationally averaged structures of R0 = 5.34 and 4.40 A, respectively. The above results are in good accord with experimental in...

A comparative icMRCI study of some NO+, NO and NO− electronic ground state properties

Potential energy, electric field gradient (EFG) at both nuclei, and electric dipole moment functions for the electronic ground states of NO+, NO and NO− were calculated at the internally contracted multireference configuration interaction (icMRCI) level using augmented correlation-consistent basis sets. The changes in the EFG's with internuclear separation R were used to interpret the character of bonding in the triad of NO species. The vibrational dependences of the electric properties were estimated and the EFG's were employed to determine the 14N nuclear quadrupole coupling constants. The effects of the choice of the basis set and reference configuration space were investigated. While the results obtained for NO+ and NO served primarily to assess the quality of calculations by comparison with available experimental and theoretical data, new information was obtained on NO−, including electric property functions and some notions about the existence of metastable states.

Vibrational Spectrum and Thermochemistry of the Formyl (HCO) Radical: A Variational Study by the Coupled Cluster CCSD(T) Method with Complete Basis Set Extrapolation

The potential energy surface for the ground state of HCO was obtained with 133 single-point energies calculated with use of the augmented correlation-consistent polarized basis sets of triple-, quadruple-, and quintuple-ζ quality and extrapolated then to the complete basis set level. Calculations are at the coupled-cluster singles and doubles level augmented by a perturbative correction for connected triple excitations CCSD(T). The relativistic and core−valence corrections were taken into consideration. A variational calculation of the HCO vibrational spectrum was performed in a basis of products of the eigenfunctions of harmonic oscillators expressed through Hermite polynomials. Infrared intensities of the lowest excitations were evaluated through calculations of matrix elements of the dipole moment for the relevant transitions. The expectation values of the structural and rotational parameters of HCO were computed. Values of Cp°, S°, and (HT° − H0°) are presented for temperatures up to 2000 K.

Potential energy surface and rovibrational states of the ground Ar–HI complex

A potential energy surface for the ground electronic state of the Ar-HI van der Waals complex is calculated at the coupled-cluster with single and double excitations and a noniterative perturbation treatment of triple excitations [CCSD(T)] level of theory. Calculations are performed using for the iodine atom a correlation consistent triple-zeta valence basis set in conjunction with large-core Stuttgart-Dresden-Bonn relativistic pseudopotential, whereas specific augmented correlation consistent basis sets are employed for the H and Ar atoms supplemented with an additional set of bond functions. In agreement with previous studies, the equilibrium structure is found to be linear Ar-I-H, with a well depth of 205.38 cm(-1). Another two secondary minima are also predicted at a linear and bent Ar-H-I configurations with well depths of 153.57 and 151.57 cm(-1), respectively. The parametrized CCSD(T) potential is used to calculate rovibrational bound states of Ar-HI/Ar-DI complexes, and the vibrationally averaged structures of the different isomers are determined. Spectroscopic constants are also computed from the CCSD(T) surface and their comparison with available experimental data demonstrates the quality of the present surface in the corresponding configuration regions.

Evaluation of carbohydrate molecular mechanical force fields by quantum mechanical calculations

A quantitative evaluation of 20 second-generation carbohydrate force fields was carried out using ab initio and density functional methods. Geometry-optimized structures (B3LYP/6-31G(d)) and relative energies using augmented correlation consistent basis sets were calculated in gas phase for monosaccharide carbohydrate benchmark systems. Selected results are: (i) The interaction energy of the α- d-glucopyranose·H 2O heterodimer is estimated to be 4.9 kcal/mol, using a composite method including terms at highly correlated (CCSD(T)) level. Most molecular mechanics force fields are in error in this respect; (ii) The 3E envelope ( south) pseudorotational conformer of methyl 5-deoxy-β- d-xylofuranoside is 0.66 kcal/mol more stable than the 3E envelope ( north) conformer and the α-anomer of methyl d-glucopyranoside is 0.82 kcal/mol more stable than the β-anomer; (iii) The relative energies of the ( gg, gt and tg) rotamers of methyl α- d-glucopyranoside and methyl α- d-galactopyranoside are (0.13, 0.00, 0.15) and (0.64, 0.00, 0.77) kcal/mol, respectively. The results of the quantum mechanical calculations are compared with the results of calculations using the 20 second-generation carbohydrate force fields. No single force field is consistently better than the others for all the test cases. A statistical assessment of the performance of the force fields indicates that CHEAT(95), CFF, certain versions of Amber and of MM3 have the best overall performance, for these gas phase monosaccharide systems.

Franck-Condon simulation of the single vibronic level emission spectra of HSiF and DSiF including anharmonicity.

Potential energy functions (PEFs) of the X (1)A(') and A (1)A(") states of HSiF have been computed using the coupled-cluster single-double plus perturbative triple excitations and complete-active-space self-consistent-field multireference internally contracted configuration interaction methods, respectively, employing augmented correlation-consistent polarized-valence quadruple-zeta basis sets. For both electronic states of HSiF and DSiF, anharmonic vibrational wavefunctions and energies of all three modes have been calculated variationally with the ab initio PEFs and using Watson's Hamiltonian for nonlinear molecules. Franck-Condon factors between the two electronic states, allowing for Duschinsky rotation, were computed using the calculated anharmonic vibrational wavefunctions. These Franck-Condon factors were used to simulate the single vibronic level (SVL) emission spectra recently reported by Hostutler et al. in J. Chem. Phys. 114, 10728 (2001). Excellent agreement between the simulated and observed spectra was obtained for the A (1)A(")(1,0,0)-->X (1)A(') SVL emission of HSiF. Discrepancies between the simulated and observed spectra of the A (1)A(")(0,1,0) and (1,1,0) SVL emissions of HSiF have been found. These are most likely, partly due to experimental deficiencies and, partly to inadequacies in the ab initio levels of theory employed in the calculation of the PEFs. Based on the computed Franck-Condon factors, minor revisions of previous vibrational assignments are suggested. The calculated anharmonic wave functions of higher vibrational levels of the X (1)A(') state show strong mixings between the three vibrational modes of HSi stretching, bending, and SiF stretching.

The binding energies of the D2d and S4 water octamer isomers: high-level electronic structure and empirical potential results.

The MP2 complete basis set (CBS) limit for the binding energy of the two low-lying water octamer isomers of D2d and S4 symmetry is estimated at -72.7+/-0.4 kcal/mol using the family of augmented correlation-consistent orbital basis sets of double through quintuple zeta quality. The largest MP2 calculation with the augmented quintuple zeta (aug-cc-pV5Z) basis set produced binding energies of -73.70 (D2d) and -73.67 kcal/mol (S4). The effects of higher correlation, computed at the CCSD(T) level of theory, are estimated at <0.1 kcal/mol. The newly established MP2/CBS limit for the water octamer is reproduced quite accurately by the newly developed all atom polarizable, flexible interaction potential (TTM2-F). The TTM2-F binding energies of -73.21 (D2d) and -73.24 kcal/mol (S4) for the two isomers are just 0.5 kcal/mol (or 0.7%) larger than the MP2/CBS limit.

Ab initio potential energy and dipole moment surfaces, infrared spectra, and vibrational predissociation dynamics of the Cl−35⋯H2/D2 complexes

Three-dimensional potential energy and dipole moment surfaces of the Cl−–H2 system are calculated ab initio by means of a coupled cluster method with single and double excitations and noniterative correction to triple excitations with augmented correlation consistent quadruple-zeta basis set supplemented with bond functions, and represented in analytical forms. Variational calculations of the energy levels up to the total angular momentum J=25 provide accurate estimations of the measured rotational spectroscopic constants of the ground van der Waals levels n=0 of the Cl−⋯H2/D2 complexes although they underestimate the red shifts of the mid-infrared spectra with v=0→v=1 vibrational excitation of the monomer. They also attest to the accuracy of effective radial interaction potentials extracted previously from experimental data using the rotational RKR procedure. Vibrational predissociation of the Cl−⋯H2/D2(v=1) complexes is shown to follow near-resonant vibrational-to-rotational energy transfer mechanism so that more than 97% of the product monomers are formed in the highest accessible rotational level. This mechanism explains the strong variation of the predissociation rate with isotopic content and nuclear spin form of the complex. Strong deviation of the observed relative abundances of ortho and para forms of the complexes from those of the monomers is qualitatively explained by the secondary ligand exchange reactions in the ionic beam, within the simple thermal equilibrium model. Positions and intensities of the hot v=0, n=1→v=1, n=1 and combination v=0, n=0→v=1, n=1 bands are predicted, and implications to the photoelectron spectroscopy of the complex are briefly discussed.

Structure and bonding of ArClF: Intermolecular potential surface

AbstractThe ground‐state potential surface of the Ar‐ClF complex is determined by restricted coupled‐cluster with single and double excitations and a noniterative perturbation treatment of triple excitation (RCCSD(T)) calculations, using augmented correlation consistent basis sets supplemented with an additional set of midbond functions. Three local minima are found for the Ar‐ClF, which correspond to linear Ar‐Cl‐F and Ar‐F‐Cl configurations and a near T‐shaped structure. The well depths and the equilibrium distances are 283.62 cm−1 at 3.84 Å and 128.96 cm−1 at 4.31 Å for the linear ones and 173.13 cm−1 at 3.58 Å for the one at θ = 107.5°.Bound‐state calculations are carried out and the linear Ar‐Cl‐F structure is found to be the most stable one, in accordance with the experiment. Dissociation energies, intermolecular distances, and vibrational frequencies are computed and compared with available experimental data.

SO 2 revisited: Impact of tight d augmented correlation consistent basis sets on structure and energetics

The total energies, atomization energies, molecular structures, and harmonic vibrational frequencies of SO2 have been determined using the newly revised correlation consistent basis sets, cc-pV(n+d)Z, with n=2–5. The impact of the additional tight d functions on the energies, structures, and frequencies as well as the convergence of these quantities to the complete basis set (CBS) limit is examined. Overall, the revised sets result in faster convergence to the CBS limit. The effect of the additional tight d function is particularly dramatic for the lower level, double zeta and triple zeta, basis sets.

Structural and thermochemical properties of the hydroxymethyl (CH2OH) radical: A high precision ab initio study

The variational solution of the CH2OH nuclear problem was performed by treatment of CH2OH as a planar molecule with highly anharmonic vibrations. A sophisticated dynamic model to describe the structural flexibility of CH2OH was applied. The detailed analysis of the rovibrational Hamiltonian is shown. The electron problem solution was obtained by use of the coupled cluster electron correlation technique and the augmented correlation-consistent polarized basis sets of triple- and quadruple-ζ qualities. The geometry and energy parameters were extrapolated to the complete basis set limit. The partition functions of CH2OH were calculated by the explicit summation of vibrational and rotational levels. The heat of formation of CH2OH, ΔfH∘(298.15 K)=−17.0±0.7 kJ/mol, was calculated by a study of the CH2OH→CH2O+H reaction using the augmented basis set of quintuple-ζ quality and the relativistic and core-valence corrections of the total energies. Some structural and thermodynamic properties of CH2O are reported.

Ab Initio Study of the Interaction Hyperpolarizabilities of HCN−HF and HNC−HF Complexes

The effects of the intermolecular interaction on dipole moment (μ), the mean (a) and anisotropy (Δα) of the polarizability, and the first and second hyperpolarizabilities (β and y, respectively) of HCN-HF and HNC-HF complexes have been calculated in finite-field approach. The augmented correlation-consistent basis sets x-aug-cc-pVXZ (x = s, d, t; X = D, T, Q) are employed to study the effects of the basis sets. Using the d-aug-cc-pVTZ basis set, we calculated the electric properties at the coupled-cluster theory with single and double substitutions and perturbatively linked triple excitations, CCSD(T) level. The electron correlation effects for those electric properties are discussed. The value of each electric property calculated for HCN-HF is less than that for HNC-HF. The μ = 2.2918 au, a = 23.186 au, Δα = 14.393 au, β = -6.03 au, and γ = 2553.4 au for HCN-HF; μ = 2.3338 au, a = 24.383 au, Δα = 14.875 au, β = 7.60 au, and y = 3049.3 au for HNC-HF. The electric properties coming from the interaction parts are as follows: μ i n t ) = 0.3908 au (17.1%), α i n t = 0.181 au (0.8%), Δα i n t = 4.300 au (29.9%), β i n t = 6.02 au (-99.8%), and γ i n t = -492.0 au (-19.3%) for HCN-HF; μ i n t = 0.4080 au (17.5%), α i n t = -0.084 au (0.3%), Δα i n t = 5.041 au (33.9%), β i n t = -7.20 au (-94.7%), and γ i n t = -931.7 au(-30.6%) for HNC-HF. The estimated electron correlation corrections are β c o r r = 6.59 au and γ c o r r = 549.2 au for HCN-HF and β c o r r = -9.49 au and γ c o r r = 1056.5 au for HNC-HF.

Development of Quantum Chemistry-Based Force Fields for Poly(ethylene oxide) with Many-Body Polarization Interactions

A methodology for consistent development of the quantum chemistry-based force fields with and without many-body polarizable terms is described. Adequate levels of theory and basis sets for determination of the relative conformational energetics, repulsion and dispersion nonbonded parameters, dipole moments, and molecular polarizability are established. Good agreement between the quantum chemistry-based repulsion and dispersion parameters and those previously obtained by fitting crystal structures of poly(oxymethylene) is obtained. Hartree−Fock (HF) calculations with augmented correlation consistent basis sets are adequate for the determination of repulsion parameters, whereas a double extrapolation to improved treatments of electron correlations and larger basis sets is needed to obtain dispersion parameters. Partial charges are obtained by fitting to the electrostatic grid of model compounds. Atomic polarizabilities are fitted to reproduce polarization energy around the model compounds. The density funct...