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AB-INITIO STUDIES OF CYCLIC WATER CLUSTERS (H2O)(N), N=1-6 .3. COMPARISON OF DENSITY-FUNCTIONAL WITH MP2 RESULTS

JOURNAL OF CHEMICAL PHYSICS 1995年第11期102卷 4505-4517页

作者： XANTHEAS, SS Theory Modeling and Simulation Environmental Molecular Sciences Laboratory Pacific Northwest Laboratory Richland Washington 99352

The optimal structures and harmonic vibrational frequencies of ring water clusters (H2O)n, n=1–6 are computed using density functional theory (DFT). The exchange functionals of Slater (S), Becke (B), the correlation functionals of Lee–Yang–Parr (LYP), Vosko–Wilk–Nusair (VWN), Perdew’s local (PL), and gradient‐corrected (P86) as well as their combinations are used to perform benchmark calculations on the water monomer and dimer. We use the augmented correlation‐consistent polarized valence orbital basis set of double (aug‐cc‐pVDZ) and triple zeta quality (aug‐cc‐pVTZ) in order to compare the DFT with earlier MP2 results [J. Chem. Phys. 99, 8774 (1993); 100, 7523 (1994)]. Better overall agreement with the MP2 and experimental results for the water monomer and dimer is observed for the B–LYP and B–P86 functional combinations. The optimal structures, harmonic vibrational frequencies, and energetics of the clusters trimer through hexamer are computed at the B–LYP/aug‐cc‐pVDZ level of theory. This functional combination yields structures, energetics, and trends with cluster size that are in good agreement with the corresponding MP2 results. ? 1995 American Institute of Physics.

关键词： WATER COMPARATIVE EVALUATIONS PERTURBATION THEORY STRUCTURE FACTORS OPTIMIZATION HARMONIC OSCILLATORS CORRELATION FUNCTIONS DIMERS POLYATOMIC MOLECULES

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AB-INITIO STUDIES OF CYCLIC WATER CLUSTERS (H2O)N, N = 1-6 .1. OPTIMAL STRUCTURES AND VIBRATIONAL-SPECTRA

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JOURNAL OF CHEMICAL PHYSICS 1993年第11期99卷 8774-8792页

作者： XANTHEAS, SS DUNNING, TH Theory Modeling and Simulation Molecular Science Research Center Pacific Northwest Laboratory Richland Washington 99352

The optimal structures and harmonic vibrational frequencies of cyclic water clusters, (H2O)n, have been determined at the Hartree-Fock (for n = 2-6) and second order perturbation theory (for n = 2-4) levels of theory with an augmented correlation consistent double zeta basis set. At the MP2 level this basis set yields very accurate results for the structure, dipole moment, and polarizability of the water monomer as well as results of comparable accuracy for the structure, binding energy, and harmonic vibrational frequencies of the water dimer. The optimal structure of (H2O)4 and the harmonic frequencies of (H2O)3,4 are the first ones reported at a correlated level for these species. Analysis of the structural trends reveals that the separation between neighboring oxygen atoms decreases exponentially with increasing cluster size. The predicted R0(O-O) for the ring hexamer is less than 0.02 angstrom shorter than the interoxygen separation in ice Ih. Furthermore, the trends in the harmonic vibrational frequencies suggest that, for large clusters, the intramolecular bends are blue shifted by approximately 70 cm-1 with respect to the monomer frequency. The frequencies corresponding to the ''free'' OH stretches show little (less-than-or-equal-to 50 cm-1) shift to the blue for n = 2-6, whereas the ones corresponding to the ''bridge'' hydrogens are shifted to the red by approximately 500 cm-1 with respect to the average of the harmonic stretching frequencies in water.

关键词： AB INITIO CALCULATIONS WATER molecular CLUSTERS OPTIMIZATION GEOMETRY VIBRATIONAL STATES HARMONIC OSCILLATORS HARTREE?FOCK METHOD PERTURBATION THEORY DIPOLE MOMENTS POLARIZABILITY

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Critical study of fluoride water interactions

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JOURNAL OF PHYSICAL CHEMISTRY 1996年第10期100卷 3989-3995页

作者： Xantheas, SS Dang, LX Theory Modeling and Simulation Environmental Molecular Sciences Laboratory Pacific Northwest National Laboratory Richland Washington 99352

A new parametrization of the fluoride-water interaction within a polarizable water model is presented. Because of the absence of accurate experimental data for the enthalpy of formation of the F-(H2O) cluster, the results of ab-initio calculations were used to parametrize the ion-water interaction. The ab-initio results suggest that this interaction is 10% stronger than what was previously thought. The accuracy of the present parametrization was evaluated by comparing the model potential with the ab-initio results along the minimum energy profile for the fluoride-water interaction for various F-O separations. The energetic and structural properties of the clusters F-(H2O)(n), n = 1-10, as well as of aqueous fluoride solution are studied using molecular dynamics simulation techniques. The stronger ion-water interaction results in the appearance of interior states (configurations in which the ion is ''solvated'' by water molecules) for finite clusters with six or more water molecules. The results of the aqueous ionic solution simulations provide a reasonable description of many structural and thermodynamic properties of the solvated ion such as the solvation enthalpy, the radial distribution function, and the hydration number.

关键词： Molecules Interaction energies Ab initio calculations Cluster chemistry Enthalpy

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THEORETICAL-STUDIES OF SULFUROUS SPECIES OF IMPORTANCE IN ATMOSPHERIC CHEMISTRY .1. CHARACTERIZATION OF THE HSO AND SOH ISOMERS

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JOURNAL OF PHYSICAL CHEMISTRY 1993年第25期97卷 6616-6627页

作者： XANTHEAS, SS DUNNING, TH Theory Modeling and Simulation Molecular Science Research Center Pacific Northwest Laboratory Richland WA 99352 United States

The molecular structures, relative energies, and vibrational frequencies of the two stable isomers formed by the addition of (H(S))-S-2 to SO(X3SIGMA-), namely, HSO and SOH, are computed using multiconfiguration wave functions and correlation-consistent basis sets of up to quintuple zeta quality. Contrary to results from previous calculations, the HSO isomer is predicted to be more stable than the SOH isomer by 5.4 kcal/mol. The barrier for the migration of the H atom between the two isomers is computed to be 46.3 kcal/mol. The transition state for the isomerization of the two species lies below the dissociation limit to H(S-2) and SO(X3SIGMA-), which is calculated to be 56.2 kcal/mol above the HSO minimum. The minimum energy paths corresponding to the addition of H(S-2) to SO(X3SIGMA-) to form HSO and SOH are also computed;a barrier of 2.4 kcal/mol is predicted for the addition of hydrogen to the oxygen side of SO. Finally, upper limits for DELTAH(f)-degrees-298 for HSO and SOH are estimated at -6.1 +/- 1.3 and -0.7 +/- 1.3 kcal/mol, respectively. The latter implies that HSO can be involved in a catalytic cycle that depletes ozone in the atmosphere.

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COMPUTER-simulationS OF NACL ASSOCIATION IN POLARIZABLE WATER

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JOURNAL OF CHEMICAL PHYSICS 1994年第5期100卷 3757-3766页

作者： SMITH, DE DANG, LX Theory Modeling and Simulation Molecular Science Research Center Pacific Northwest Laboratory Richland Washington 99352

Classical molecular dynamics computer simulations have been used to investigate the thermodynamics and kinetics of sodium chloride association in polarizable water. The simulations make use of the three-site polarizable water model of Dang [J. Chem. Phys. 97, 2659 (1992)], which accurately reproduces many bulk water properties. The model's static dielectric constant and relaxation behavior have been calculated and found to be in reasonable agreement with experimental results. The ion-water interaction potentials have been constructed through fitting to both experimental gas-phase binding enthalpies for small ion-water clusters and to the measured structures and solvation enthalpies of ionic solutions. Structural properties and the potential of mean force for sodium chloride in water have been calculated. In addition, Grote- Hynes theory has been used to predict dynamical features of contact ion-pair dissociation. All of the calculated ionic solution properties have been compared with results from simulations using the extended simple point charge (SPC/E), nonpolarizable water model [J. Phys. Chem. 91, 6296 (1987)]. The dependence on polarizability is found to be small, yet measurable, with the largest effects seen in the solvation structure around the highly polarizable chlorine anion. This work validates the use of some nonpolarizable water models in simulations of many condensed-phase systems of chemical and biochemical interest.

关键词： ASSOCIATION COMPUTERIZED simulation CLASSICAL MECHANICS THERMODYNAMICS KINETICS SODIUM CHLORIDES WATER POLARIZABILITY POTENTIALS ION?MOLECULE COLLISIONS ENTHALPY STRUCTURE FACTORS

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STRUCTURES AND ENERGETICS OF F-(H2O)(N), N=1-3, CLUSTERS FROM AB-INITIO CALCULATIONS

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JOURNAL OF PHYSICAL CHEMISTRY 1994年第51期98卷 13489-13497页

作者： XANTHEAS, SS DUNNING, TH Theory Modeling and Simulation Environmental Molecular Sciences Laboratory Pacific Northwest Laboratory Richland WA 99352 United States

We have computed the optimal structures and harmonic vibrational frequencies of the F-(H2O)(n), n = 1-3, clusters at the MP2 level of theory. For the n = 2 and 3 cases, the minimum-energy configurations correspond to asymmetric structures where the ion sits outside the water cluster. The electronic energy difference between these configurations and the symmetric ones, in which the ion is completely surrounded by water molecules is, however, very small (0.5-1.5 kcal/mol). When zero-point vibrational energy corrections are included, the energy difference becomes negligible and, in the n = 3 case, it is reversed making the symmetric structure favorable by 0.1 kcal/mol. It is therefore concluded that the dynamical effects in addition to the static features of the potential energy surface are important in determining the most probable orientation of the water molecules around the ion. The energy differences between the critical points were analyzed in terms of the relative magnitudes of the second- and higher-order interaction energy terms. We have found that electron correlation is very important in the computation of accurate energy differences and many-body interaction energy terms, especially for the n = 2 and 3 cases.

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AB-INITIO STUDIES OF CYCLIC WATER CLUSTERS (H2O)(N), N=1-6 .2. ANALYSIS OF MANY-BODY INTERACTIONS

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JOURNAL OF CHEMICAL PHYSICS 1994年第10期100卷 7523-7534页

作者： XANTHEAS, SS Theory Modeling and Simulation Molecular Science Research Center Pacific Northwest Laboratorya) Richland Washington 99352

The magnitudes of the two- through six-body energy terms and their contribution to the interaction energy of small ring water clusters (n=2-6) are computed at the Hartree-Fock (HF) and, second-through fourth-order many-body perturbation (MP2, MP4) levels of theory. The analysis is performed at the minimum energy geometries reported earlier [J. Chem. Phys. 99, 8774 (1993)]. The correlation correction is found to account for a 10%-20% increase in the individual two-body terms and a much larger increase of 75% for the three-body and 200% for the small four-body terms. The MP4 results are found to differ only slightly (<2%) from the corresponding MP2 results. We have found that three-body terms have a significant contribution as high as 30% to the interaction energy of the larger clusters and that four-body and higher order-terms are negligible. The total and incremental association energies for;the processes n H2O-->(H2O)(n) and (H2O)(n-1) + H2O-->(H2O)(n), n=2-6 are also reported.

关键词： AB INITIO CALCULATIONS WATER molecular CLUSTERS MANY?BODY PROBLEM HARTREE?FOCK METHOD PERTURBATION THEORY CORRELATIONS BINDING ENERGY

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THEORETICAL ESTIMATE OF THE ENTHALPY OF FORMATION OF HSO AND THE HSO SOH ISOMERIZATION ENERGY

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JOURNAL OF PHYSICAL CHEMISTRY 1993年第1期97卷 18-19页

作者： XANTHEAS, SS DUNNING, TH Theory Modeling and Simulation Molecular Science Research Center Pacific Northwest Laboratory Richland WA 99352 United States

The enthalpy of formation of HSO is estimated to be -5.4 +/- 1.3 kcal/mol through a series of multireference configuration interaction (MR-CI) calculations that systematically expand the orbital basis set. The estimated value of DELTAH(f)degrees suggests that HSO may well be involved in a catalytic cycle that depletes ozone in the atmosphere. In contrast to all earlier theoretical studies, the computed energy difference between the HSO and SOH isomers is estimated to be 5.4 kcal/mol, with the HSO isomer being more stable.

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STRUCTURES OF ANION WATER CLUSTERS - H-(H2O)N, N = 1-3

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JOURNAL OF PHYSICAL CHEMISTRY 1992年第19期96卷 7505-7506页

作者： XANTHEAS, SS DUNNING, TH Theory Modeling and Simulation Molecular Science Research Center Pacific Northwest Laboratory Richland WA 99352 United States

The structures of hydride ion-water clusters with up to three water molecules have been computed using accurate ab initio techniques. The water molecules are not distributed symmetrically around the anion. Rather, they cluster on one side of the anion so as to retain a measure of hydrogen bonding. The calculated binding energies (including zero-point energies) for successive addition of water molecules to the hydride ion are 17.4, 14.8, and 13.7 kcal/mol.

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THE STRUCTURE OF THE WATER TRIMER FROM ABINITIO CALCULATIONS

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JOURNAL OF CHEMICAL PHYSICS 1993年第10期98卷 8037-8040页

作者： XANTHEAS, SS DUNNING, TH Theory Modeling and Simulation Molecular Science Research Center Pacific Northwest Laboratorya) Richland Washington 99352

The first fully optimized structure of the water trimer at the MP2 level of theory is reported. It corresponds to a cyclic chiral structure in which all O-O separations are equal to 2.80 angstrom, the O(alpha)H ... O(beta) hydrogen bonds are nonlinear, and two of the terminal hydrogens lie on one side of the O-O-O plane and the third lies on the other. This structure is in qualitative agreement with that reported recently by Pugliano and Saykally [Science 257, 1937 (1992)]. However, the calculations predict the O-O separations to be substantially shorter than those used to fit the far-infrared vibration-rotation-tunneling spectrum. Nonetheless, the computed structure reproduces the measured rotational constants of (D2O)3;the errors are < 1% for A and B and 6% for C An energy analysis yields a three-body term of 2.3 kcal/mol (approximately 15% of D(e) with respect to three isolated water molecules).

关键词： WATER POLYATOMIC MOLECULES AB INITIO CALCULATIONS OPTIMIZATION HYDROGEN BONDS THREE?BODY PROBLEM molecular STRUCTURE BINDING ENERGY

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