Potential Energy Surface Of H2O Research Articles

Models for boronic acid receptors II: a computational structural, bonding, and thermochemical investigation of the RB(OH)2∙H2O∙NH3 and RB(−OCH2CH2O−)∙NH3∙H2O potential energy surfaces (R = H, methyl, phenyl, and ortho-methyl-phenyl)

Models for boronic acid receptors II: a computational structural, bonding, and thermochemical investigation of the RB(OH)2∙H2O∙NH3 and RB(−OCH2CH2O−)∙NH3∙H2O potential energy surfaces (R = H, methyl, phenyl, and ortho-methyl-phenyl)

Cuts through the manifold of molecular H2O potential energy surfaces in liquid water at ambient conditions

The fluctuating hydrogen bridge bonded network of liquid water at ambient conditions entails a varied ensemble of the underlying constituting H2O molecular moieties. This is mirrored in a manifold of the H2O molecular potentials. Subnatural line width resonant inelastic X-ray scattering allowed us to quantify the manifold of molecular potential energy surfaces along the H2O symmetric normal mode and the local asymmetric O-H bond coordinate up to 1 and 1.5 Å, respectively. The comparison of the single H2O molecular potentials and spectroscopic signatures with the ambient conditions liquid phase H2O molecular potentials is done on various levels. In the gas phase, first principles, Morse potentials, and stepwise harmonic potential reconstruction have been employed and benchmarked. In the liquid phase the determination of the potential energy manifold along the local asymmetric O-H bond coordinate from resonant inelastic X-ray scattering via the bound state oxygen 1s to [Formula: see text] resonance is treated within these frameworks. The potential energy surface manifold along the symmetric stretch from resonant inelastic X-ray scattering via the oxygen 1s to [Formula: see text] resonance is based on stepwise harmonic reconstruction. We find in liquid water at ambient conditions H2O molecular potentials ranging from the weak interaction limit to strongly distorted potentials which are put into perspective to established parameters, i.e., intermolecular O-H, H-H, and O-O correlation lengths from neutron scattering.

Externally Corrected CCSD with Renormalized Perturbative Triples (R-ecCCSD(T)) and the Density Matrix Renormalization Group and Selected Configuration Interaction External Sources.

We investigate the renormalized perturbative triples correction together with the externally corrected coupled-cluster singles and doubles (ecCCSD) method. We use the density matrix renormalization group (DMRG) and heat-bath CI (HCI) as external sources for the ecCCSD equations. The accuracy is assessed for the potential energy surfaces of H2O, N2, and F2. We find that the triples correction significantly improves upon ecCCSD, and we do not see any instability of the renormalized triples with respect to dissociation. We explore how to balance the cost of computing the external source amplitudes against the accuracy of the subsequent CC calculation. In this context, we find that very approximate wave functions (and their large amplitudes) serve as an efficient and accurate external source. Finally, we characterize the domain of correlation treatable using the ecCCSD and renormalized triples combination studied in this work via a well-known wave function diagnostic.

Models for boronic acid receptors: a computational structural, bonding, and thermochemical investigation of the HB(OH)2∙H2O∙NH3 and HB(-O-CH2-CH2-O-)∙NH3∙H2O potential energy surfaces

Results of structural and thermochemical calculations involving boronic acid, HB(OH)2, and the corresponding ethylene glycol ester, HB(-O-CH2-CH2-O-), in the presence of explicit NH3 and/or H2O molecules are reported. Calculations were performed in a polarizable continuum model (PCM) water solution and in the gas phase using density functional theory (DFT) and second-order Moller-Plesset perturbation theory (MP2) with the Dunning-Woon aug-cc-pVTZ basis set. Different classes of local minima on the HB(OH)2·NH3·H2O and HB(-O-CH2-CH2-O-)·NH3·H2O potential energy surfaces (PESs) in PCM water solution have been identified: (1) structures with a N→B dative bond, [H3N→BH(OH)2]·H2O, and [H3N→B(H)(-O-CH2-CH2-O-)]·H2O, where the H2O is involved in hydrogen bonding; (2) water-inserted structures involving either a novel O→B dative bond, H3N·H(H)O→BH(OH)2, and H3N···H(H)O→B(H)(-O-CH2-CH2-O-) where the H2O molecule remains essentially intact or lower-energy zwitterionic arrangements in which a water H atom has been transferred to the ammonia, [H4N]+[HO-BH(OH)2]−, and [H4N]+[BH(OH)(-OCH2-CH2-O-)]−; (3) structures where both the NH3 and H2O molecules are exclusively involved in hydrogen bonding. In these simple model systems, arrangements with N→B dative bonds, and some structures with only O···H and N···H hydrogen bonds, are ca. 5–6 kcal/mol lower in energy than either of the corresponding water-inserted structures.

Quantum wave-packet studies on ion–molecule reaction with and without Coriolis-coupling effect

The time-dependent quantum scattering calculation with Chebyshev wave packet propagation scheme has been carried out based on an accurate electronic potential energy surface of H2O+(X4A″). Due to the influence of the deep potential well, the reaction probability of [Formula: see text] shows resonance structures regardless of the Coriolis-coupling (CC) effect or centrifugal sudden (CS) approximation. In the range of collision energy 0.0–1.0 eV, the integral cross section obtained by the CS approximation calculation is smaller than that by the CC calculation, which indicates that the CC effect plays a significant role in the title reaction.

The hydration structure of carbon monoxide by ab initio methods.

The solvation of carbon monoxide (CO) in liquid water is important for understanding its toxicological effects and biochemical roles. In this paper, we use ab initio molecular dynamics (AIMD) and CCSD(T)-F12 calculations to assess the accuracy of the Straub and Karplus molecular mechanical (MM) model for CO(aq). The CCSD(T)-F12 CO-H2O potential energy surfaces show that the most stable structure corresponds to water donating a hydrogen bond to the C center. The MM-calculated surface incorrectly predicts that the O atom is a stronger hydrogen bond acceptor than the C atom. The AIMD simulations indicate that CO is solvated like a hydrophobic solute, with very limited hydrogen bonding with water. The MM model tends to overestimate the degree of hydrogen bonding and overestimates the atomic radius of the C atom. The calculated Gibbs energy of hydration using the TIP3P water model is in good agreement with the experiment (9.3 kJ mol-1 expt. vs 10.7 kJ mol-1 calc.). The calculated diffusivity of CO (aq) in TIP3P-model water was 5.1×10-5 cm2/s calc., more than double the experimental value of 2.3×10-5 cm2/s. The hydration energy calculated using the TIP4P-FB water model is in poorer agreement with the experiment (ΔG = 6.8 kJ/mol) but the diffusivity is in better agreement (D=2.5±0.1×10-5 cm2/s).

Globally accurate ab initio based potential energy surface of H2O+(X 4A″)**Project supported by the National Natural Science Foundation of China (Grant Nos. 11304185 and 11074151), China Postdoctoral Science Foundation (Grant No. 2014M561957), the Postdoctoral Innovation Project of Shandong Province, China (Grant No. 201402013), and the Shandong Provincial Natural Science Foundation, China (Grant No. ZR2014AM022).

A globally accurate potential energy surface is reported for the electronic ground-state H2O+. The ab initio energies utilized to map the potential energy surface are calculated at the multireference configuration interaction method employing the aug-cc-pVQZ basis set and the full valence complete active space wave function as reference. In order to improve accuracy of the resulting raw ab initio energies, they are then extrapolated to the complete basis set limit and most importantly to the full configuration-interaction limit by semiempirically correcting the dynamical correlation using the double many-body expansion-scaled external correlation method. The topographical features of the current potential energy surface were examined in detail, which agree nicely with those of other theoretical work.

Addition complex and insertion isomers on the potential energy surface of the reaction of indium dimer with water studied with relativistic ECP

Stationary points on the lowest singlet and triplet In2 + H2O potential energy surfaces (PESs) have been explored using the coupled cluster method, including single and double excitations with perturbative triples (CCSD(T)), and the density functional theory (DFT), employing the effective core potential (ECP) for indium (In), which accounts for scalar relativistic effects, with the triple-zeta quality basis set. The CCSD(T) calculated binding energy and anharmonic ν2-bending mode frequency for the triplet ground-state addition complex, In2… OH2(3B1), are consistent with the complex detected in the matrix isolation infrared (IR) spectroscopic study under the thermal conditions. The two minimum energy crossing points between the triplet and the singlet PESs that have been located between the structures of In2…OH2 and the transition state for the O–H bond breakage are not likely to be thermally accessible under the low-temperature matrix conditions. With the CCSD(T)-calculated In2 + H2O reaction profile and anharmonic vibrational frequencies for several In2(H)(OH) insertion product isomers, we support the IR matrix isolation detection (by two experimental groups) of the lowest energy singlet double-bridged In(μ-H)(μ-OH)In isomer. For the proposed two-step mechanism of H2 elimination from the In2(H)(OH) species, the estimated energy barriers are also compatible with experiment.

Potential energy surface of H2O on Al{111} and Rh{111} from theoretical methods

The potential energy surfaces of molecular water on the Al{111} and on the Rh{111} metal surfaces have been investigated using density functional theory. Similar landscapes were found on both surfaces. In the only minimum found, the water molecule is monocoordinated to the surface via the oxygen atom (top configuration) with its plane nearly parallel to the surface. The maxima are around the bridge and hollow configurations and no local minima or maxima were found. Along the investigated minimum energy pathways, no strong preferential orientation of the water dipole was found, as long as the molecular plane is nearly parallel to the surface.

Dynamical studies and product analysis of O(1D) + H2/D2 reactions

The aim of this study was to analyse the dynamics of O(1D) + H2/D2 reactions using quasiclassical trajectory calculations on a double-valued potential energy surface for H2O. Produced on the photodissociation of stratospheric ozone, the excited oxygen atom is a highly reactive species whose chemistry plays a key role in the ozone depletion cycle. In order to make comparisons with experiment, we studied these reactions at fixed translational collision energies. In particular, we consider the reactive cross sections, the thermal rate constants, the opacity function, and the differential cross sections. In addition, we also study the energy distribution of the products and compare the results with experiment and calculations based on phase space statistical theory. Results for the rotational population of the OH products are also compared with experimental results. The agreement between our results and experiment reinforces the accuracy of the H2O potential energy surface used.

Potential energy surface for H2O(3A″) from accurate ab initio data with inclusion of long-range interactions

A new potential energy surface for the O((3)P) + H(2) system in the lowest (3)A(") state is built using ab initio data calculated by Rogers et al. [J. Phys. Chem. A 104, 2308 (2000)] and the double many-body expansion formalism. It incorporates a semiempirical model of long-range interactions, which should play an important role at low collision energies. Preliminary quasiclassical trajectory results at 12.6 kcal/mol collision energy, show that the deeper van der Waals region described in this new surface translates into a four times higher cross section than that of Rogers' (3)A(") surface. To confirm this hypothesis, a second surface was calibrated. The two surfaces are fitted with rmsd<0.5 kcal/mol and differ mainly on the depth of the van der Waals region. That difference in the van der Waals region corresponds to a 22% lower cross section of the less deep surface, which is still three times higher than the equivalent results from Rogers' (3)A(") surface. This study reflects the importance of a correct description of van der Waals forces on potential energy surfaces.

Double-valued potential energy surface for H2O derived from accurate ab initio data and including long-range interactions

In a recent work we have been able to model the long-range interactions within the H2O molecule. Using these long-range energy terms, a complete potential energy surface has been obtained by fitting high-quality ab initio energies to a double-valued functional form in order to describe the crossing between the two lowest-potential-energy surfaces. The two diabatic surfaces are represented using the double many-body expansion model, and the crossing term is represented using a three-body energy function. To warrant a coherent and accurate description for all the dissociation channels we have refitted the potential energy functions for the H2(3Σu+), OH(2Π), and OH(2Σ) diatomics. To represent the three-body extended Hartree–Fock nonelectrostatic energy terms, V1, V2, and V12, we have chosen a polynomial on the symmetric coordinates times a range factor in a total of 148 coefficients. Although we have not used spectroscopic data in the fitting procedure, vibrational calculations, performed in this new surface using the DVR3D program suite, show a reasonable agreement with experimental data. We have also done a preliminary quasiclassical trajectory study (300 K). Our rate constant for the reaction O(1D)+H2(1Σg+)→OH(2Π)+H(2S), k(300 K)=(0.999±0.024)×10−10 cm3 molecule−1 s−1, is very close to the most recent recommended value. This kinetic result reinforces the importance of the inclusion of the long-range forces when building potential energy surfaces.

Microsolvation of the water cation in neon: Infrared spectra and potential energy surface of the H2O+–Ne open-shell ionic complex

The intermolecular potential of the H2O+–Ne open-shell ionic dimer in its doublet electronic ground state has been investigated by infrared spectroscopy in the vicinity of the O–H stretch vibrations (ν1 and ν3) and ab initio calculations at the unrestricted Møller–Plesset second-order (MP2) level with a basis set of aug-cc-pVTZ quality. The rovibrational structure of the photodissociation spectrum is consistent with a proton-bound planar H–O–H–Ne structure and a Ne–H separation of R0=1.815(5) Å. The complexation-induced redshifts are Δν1=−69 cm−1 and Δν3=−6 cm−1, respectively. Tunneling splittings observed in the perpendicular component of the ν3 hybrid band of H2O+–Ne are attributed to hindered internal rotation between the two equivalent proton-bound equilibrium structures. The interpretation of the H2O+–Ne spectrum is supported by the spectrum of the monodeuterated species, for which both the proton-bound and the deuteron-bound isomers are observed (DOH+–Ne, HOD+–Ne). The equilibrium structure of the calculated potential energy surface of H2O+–Ne has a slightly translinear proton bond, which is characterized by a Ne–H separation of Re=1.77 Å, a bond angle of φe=174°, and dissociation energies of De=756 cm−1 and D0=476 cm−1. According to the calculated potential, the exchange tunneling between the two equivalent minima occurs via the planar bridged transition state with C2v symmetry and a barrier of 340 cm−1. In general, the calculated properties of H2O+–Ne show good agreement with the experimental data. Initial steps in the microsolvation of the water cation in neon are discussed by comparing the calculated and experimental properties of H2O+–Nen (n=0–2) with neon matrix isolation data (n→∞).

Diatomics-in-molecules applied to solid hydrogen doped with

An accurate diatomics-in-molecules (DIM) representation of the first five potential energy surfaces of H2O in the singlet state is embedded in a DIM model (with induction interactions) for O(1Dg) in a solid hydrogen environment. We suggest that the absence of a barrier to formation of H2O from O(1Dg) + H2 in the isolated triatomic system is fully compatible with the existence of a stable O(1Dg) atom at a substitution site in the solid hydrogen crystal. This results from the requirement that, along the path to formation of H2O, the wave function must acquire ionic character, since H2O is a very polar molecule, but these ionic structures are penalised energetically in the many-body environment because of 3-body electrostatic interactions, effectively blocking the reaction path and conferring stability upon the O(1Dg) atom.

The lower C2v potential energy surfaces of the doublet states of H2O+: A computational study

In this paper we extend our previous study (F. Schneider, F. Di Giacomo, and F. A. Gianturco, J. Chem. Phys. 104, 5153) on the topology of the electronic states of the neutral H2O molecule in C2v symmetry by examining the lowest ten potential energy surfaces of the water molecular cation in its doublet states. The relevant electronic energy surfaces of H2O+ are shown as 2D contour maps where possible reaction pathways for several low-lying potential energy surfaces of H2O+ are clearly seen and therefore can be discussed and analyzed in some detail. The present results were obtained using ab initio multireference configuration interaction calculations at 184 nuclear arrangements, as described in our previous paper dealing with the neutral H2O.

Diatomics-in-molecules models for H2O and H2O−. II. A self-consistent description of the 1A′, 1A″, 3A′, and 3A″ states of H2O

This paper describes a small (6 to 9 basis functions) model for the potential energy surfaces relevant to the chemical reaction O(1D)+H2→OH(X 2Π)+H. The model is optimized with respect to the 1A′ and 1A″ states correlating with the reagents and products of this reaction; this is done in such a way as to simultaneously provide a qualitatively correct description of the 3A′ and 3A″ states of H2O. In this sense the model is self-consistent. In agreement with other semiempirical work, the results indicate that two 1A′ surfaces and one 1A″ surface are pertinent for a dynamical study of this reaction. The model adequately represents the most important features of H2O potential energy surfaces and is at the same time small enough to be used directly in a trajectory calculation of the reaction cross section.

A theoretical study of the interaction of N2 with water molecules. (H2O)n:N2, n=1–8.

A b initio molecular orbital calculations including correlation energy have been carried out on the interaction of a single H2O molecule with N2. The potential energy surface for H2O:N2 is found to have a minimum corresponding to a HOH ⋅⋅⋅ N2 structure with a weak (&amp;lt;2 kcal mol−1) hydrogen bond. A second, less stable, configuration corresponding to a H2O ⋅⋅⋅ N2 structure with N2 bonded side on to the oxygen of H2O was found to be either a minimum or a saddle point in the potential energy surface depending on the level of calculation. The minimal STO-3G basis set was used to investigate the interaction of up to eight H2O molecules with N2. Two types of clusters, one containing only HOH ⋅⋅⋅ N2 interactions and the other containing both HOH ⋅⋅⋅N2 and H2O ⋅⋅⋅ N2 interactions, were investigated for [N2:(H2O)n, n=2–8].

Diatomics-in-molecules calculation of the potential energy surface of H2O+: linear approach

A diatomics-in-molecules calculation of the potential energy surface for O++H2 to OH++H (linear approach) yields a 22 kcal mole-1 activation barrier. This is in contrast to a previous ab initio calculation by Chambaud et al. (1974) in which the intermediate species (O . . . H . . . H)+ is found to be bound with respect to reactants and products.

The quartic force field of H2O determined by many-body methods that include quadruple excitation effects

Many-body perturbation theory (MBPT) and coupled cluster methods are employed in an investigation of the potential energy surface of H2O in the vicinity of its equilibrium geometry. The basis set of 39 Slater-type orbitals is the same as that previously used in a configuration interaction study (limited to all single and double excitations, SD-CI) of this surface, and is capable of accounting for 80% of the total correlation energy of the molecule. Detailed comparisons among the results of the various methods are presented, with particular reference to the role of size extensivity in providing a reliable model for the prediction of the shape of the surface. The predicted quartic force field obtained by the coupled cluster doubles (CCD) and by several MBPT models is in very good agreement with experiment. The inclusion of quadruple excitations, which account for about 5% of the correlation energy, is found to have a significant effect on the shape of the surface, bringing the predicted force field into substantially better agreement with experiment than that obtained with SD-CI.

Potential energy surface of H2O+: linear approach

An SCF+CI calculation of the potential energy surface of H2O+ in Cinfinity v symmetry (linear approach) is reported. No energy barrier has been found for the chemical reaction O++H2 to OH++H. Instead, the energy of the intermediate species (O...H...H)+ is found to be 12 kcal/mole below the energy of the input products. This leads to the conclusions that the reaction can actually occur at low temperatures (interstellar clouds) and that the complete potential energy surface is worth computing.