Energetics of proton transfer in liquid water. I. Ab initio study for origin of many-body interaction and potential energy surfaces

The energetics of proton transfer in liquid water investigated by using ab initio calculation. The molecular electronic interaction of hydrated proton clusters in classified into many-body interaction elements by a new energy decomposition method. It is found that up to three-body molecular interaction is essential to describe the potential energy surface. The three-body effect mainly arises from the (non-classical) charge transfer and strongly depends on their configuration. Higher than three-body effects are small enough to be neglected. To simulate the liquid state reactions, two cluster models including all water molecules up to the second shell in the proton transfer reactions are employed. It is shown that these proton transfer reactions only involve small potential energy barriers of a few kcal/mol or less when structural rearrangement of the solvent is induced along the proton movement.     

Single-molecule precipitation of transition metal(I) chlorides in water clusters.

Metal ions in unusual oxidation states can be introduced into water clusters using a standard laser vaporization source. Such nanosolutions of a single ion in typically 50 water molecules are comparable to a 1 M bulk solution, and their chemistry can be studied in the ion trap of a Fourier transform ion cyclotron resonance mass spectrometer. We find that a strong acid like hydrogen chloride oxidizes the early transition metal vanadium to the more common +III state, while later first row transition metals retain their unusual +I oxidation state, and the binary metal chlorides M(I)Cl precipitate.     

The many-body expansion of the potential energy function for elemental clusters

The many-body expansion of the potential energy function of elemental clusters is examined in general terms in regard to its convergence for microclusters and the bulk phase. The systems Be_n and Li_n are examined in detail. For Li it is clear that the many-body expansion has no low-order convergence, but it is shown that a potential of the form gives good binding energies for Li_n (3<n?9) and also a good value for the heat of atomization of the bcc crystal.     

Ab initio potential and dipole moment surfaces for water. II. Local-monomer calculations of the infrared spectra of water clusters

We employ recent flexible ab initio potential energy and dipole surfaces [Y. Wang, X. Huang, B. C. Shepler, B. J. Braams, and J. M. Bowman, J. Chem. Phys. 134, 094509 (2011)] to the calculation of IR spectra of the intramolecular modes of water clusters. We use a quantum approach that begins with a partitioned normal-mode analysis of perturbed monomers, and then obtains solutions of the corresponding Schro?dinger equations for the fully coupled intramolecular modes of each perturbed monomer. For water clusters, these modes are the two stretches and the bend. This approach is tested against benchmark calculations for the water dimer and trimer and then applied to the water clusters (H(2)O)(n) for n = 6-10 and n = 20. Comparisons of the spectra are made with previous ab initio harmonic and empirical potential calculations and available experiments.     

Microsolvation of LiH+ in helium clusters: many-body effects and additivity models for the interaction forces

The ab initio calculation of the interaction forces between the LiH+ molecular ion, at its equilibrium geometry, and several He atoms is carried out in order to isolate and assess the importance of many-body contributions in the search for realistic energy and geometry data. The full potential energy surface (PES) with a single helium partner is obtained first by using an aug-cc-pVQZ basis set for He and higher quality ones for Li and H. The calculations were performed at the CAS-SCF plus MRCI level for the lowest potential energy surface over a total of 480 grid points of the two intermolecular Jacobi coordinates, whereas the excited state surface has also been examined in order to exclude the presence of any significant nonadiabatic interaction between the two PESs. A numerical fit of the lower surface is presented and the general physical changes of the ionic interaction when going from the lower to the upper of the two potentials are described and discussed. The fairly limited importance of many-body effects for such systems is seen from further ab initio calculations including several He atoms: our results suggest that, at least in the present case, no strong charge migration occurs after He attachment, and therefore, one could realistically model larger clusters by implementing a sum-of-potentials approach via the presently computed PES.     

Flexible, ab initio potential, and dipole moment surfaces for water. I. Tests and applications for clusters up to the 22-mer

We report full-dimensional, ab initio potential energy and dipole moment surfaces, denoted PES and DMS, respectively, for arbitrary numbers of water monomers. The PES is a sum of 1-, 2-, and 3-body potentials which can also be augmented by semiempirical long-range higher-body interactions. The 1-body potential is a spectroscopically accurate monomer potential, and the 2- and 3-body potentials are permutationally invariant fits to tens of thousands of CCSD(T)/aug-cc-pVTZ and MP2/aug-cc-pVTZ electronic energies, respectively. The DMS is a sum of 1- and 2-body DMS, which are covariant fits to tens of thousands MP2/aug-cc-pVTZ dipole moment data. We present the details of these new 2- and 3-body potentials and then extensive applications and tests of this PES are made to the structures, classical binding energies, and harmonic frequencies of water clusters up to the 22-mer. In addition, we report the dipole moment for these clusters at various minima and compare the results against available and new ab initio calculations.     

Na clusters on Na-Cl surfaces — the impact of the interface potential

We investigate the structure and energetics of Na clusters on Na-Cl surfaces. The Na-Cl substrate is taken as inert acting on the clusters constituents essentially through its interface potential which consists in a general surface attraction and is modulated by corrugation. The cluster is described as a predominantly electronic system in the spirit of the ultimate jellium model. The strong surface attraction makes planar clusters the preferred choice in any case and non-planar stable isomers do always exist. The corrugation has a large influence on the shapes, particularly for the larger clusters. But the total energy of the clusters is insensitive to these details. It can be described in terms of volume, surface, and interface energy allowing a simple estimate of the preferred geometry in dependence of the strength of the interface potential.     

Effect of nanobubbles on friction forces between hydrophobic surfaces in water

Micro- and nanoscale combined hierarchical polymer structures were fabricated by UV-assisted capillary force lithography. The method is based on the sequential application of engraved polymer molds with a UV-curable resin of polyurethane acrylate (PUA) followed by surface treatment with a trichloro(1H,1H,2H,2H-perfluorooctyl) silane in vapor phase. Two distinct wetting states were observed on these dual-roughness structures. One is “Cassie–Wenzel state” where a water droplet forms heterogeneous contact with microstructures and homogeneous contact with nanostructures. The other is “Cassie–Cassie state” where a droplet makes heterogeneous contact both with micro- and nanostructures. A simple thermodynamic model was developed to explain static contact angle, hysteresis, and wetting transition on dual-roughness structures.     

Assessment of the pairwise additive approximation and evaluation of many-body terms for water clusters

We have tested the ability of four commonly used density functionals (three of which are semilocal and one of which is nonlocal) to outperform accurate pairwise additive approximations in the prediction of binding energies for a series of water clusters ranging in size from dimer to pentamer. Comparison to results obtained with the Weizmann-1 (W1) level of wave function theory shows that while all density functionals are capable of outperforming the accurate pairwise data, the choice of basis set used is crucial to the performance of the method, and if a poor choice of basis set is made the errors obtained with density functional theory (DFT) can be larger than those obtained with the simple pairwise approximation. We have also compared the binding energies and many-body terms determined with DFT to those obtained with W1, and have found that all semilocal functionals have significant errors in the many-body components of the full interactions energy. Despite this limitation, however, we have found that, of the four functionals tested, PBE1W/MG3S is the most accurate for predicting the binding energies of the clusters.     

On the role of anion templates for the self-assembly of octanuclear copper(I) dichalcogenophosph(in)ate clusters

The octanuclear Cu^I cubic clusters [Cu₈(S₂PPh₂)₆]²⁺ (1) and [Cu₈(μ₈-Cl)(S₂PPh₂)₆]⁺ (2) have been prepared and crystallographically characterized, and their cluster bonding modes investigated with density functional theory (DFT) calculations. Both are rare examples of metal dithiophosphinate clusters and 1 is the first example of a non anion-centered or ‘empty’ dithiophosph(in)ate Cu^I₈ cube. DFT calculations indicate that the stability of the empty cluster 1 can be attributed to its strong metal–ligand interactions, with no significant Cu?Cu bonding interactions present. Comparison of the solid-state structures of 1, 2 and the analogous sulfide centered cluster [Cu₈(μ₈-S)(S₂PPh₂)₆] (3) reveals a significant contraction of the octanuclear Cu^I₈ cube upon anion encapsulation. This contraction is shown, using DFT calculations, to be predominately assignable to the ionic interaction between the Cu^I cations and the encapsulated anion center.     

Chemometric study of liquid water simulations. I. The parameters of the TIP4P model potential

The multivariate chemometric techniques two level factorial design (TLFD) and principal component analysis (PCA) were used to investigate the TIP4P model potential behavior with respect to perturbations on all intermolecular interaction parameters. The effects of these perturbations were calculated for the enthalpy of vaporization, the density, the first maximum of the radial distribution functions of the O-H and O-O pairs, and the second maximum of the radial distribution function of the O-H pair obtained from Monte Carlo simulations of liquid water at 25 degrees C. The principal effects were quantified and rationalized in terms of the pair-wise interaction potential of the TIP4P model. They also corroborate previously published sensitivity analysis results using molecular dynamics and other model potentials. In addition, significant interaction effects between some parameters of the TIP4P model potential were observed and quantified, which hardly could be obtained without such a statistic approach. These interaction effects are very regular and systematic, and their behavior has not been encountered in other chemometric studies and cannot be rationalized in terms of the functional form of the pair-wise potential.     

Functionalized thiosemicarbazone clusters of copper(I) and silver(I)

Reaction of [Cu(MeCN)(4)](+) with thiosemicarbazones bearing groups such as phenol, pyridine, or ferrocene gives tetranuclear or hexanuclear clusters with functional substituents; analogous air stable fluorescent clusters can also be prepared with Ag(I).     

Development of transferable interaction potentials for water. V. Extension of the flexible, polarizable, Thole-type model potential (TTM3-F, v. 3.0) to describe the vibrational spectra of water clusters and liquid water

We present a new parametrization of the flexible, polarizable Thole-type model for water [J. Chem. Phys. 116, 5115 (2002); J. Phys. Chem. A 110, 4100 (2006)], with emphasis in describing the vibrational spectra of both water clusters and liquid water. The new model is able to produce results of similar quality with the previous versions for the structures and energetics of water clusters as well as structural and thermodynamic properties of liquid water evaluated with classical and converged quantum statistical mechanical atomistic simulations. At the same time it yields accurate redshifts for the OH vibrational stretches of both water clusters and liquid water.     

Interaction forces between poly(amidoamine) (PAMAM) dendrimers adsorbed on gold surfaces

Interaction forces between two gold surfaces with adsorbed poly(amidoamine) (PAMAM) dendrimers (generations G3.0 and G5.0) have been investigated using colloidal probe atomic force microscopy (AFM). In the absence of dendrimers or at their low concentrations, an attractive force derived from the van der Waals interaction was observed. On the other hand, this attractive interaction changed to repulsion with increasing dendrimer concentration. The origin of the repulsion can be attributed to either an electric double layer interaction or a steric effect of the adsorbed dendrimers, depending on the concentration of dendrimer. The steric hindrance was also influenced by the generation of the dendrimer; the force-detectable distance in the presence of PAMAM G5.0 dendrimer was slightly longer than that in the presence of G3.0 dendrimer. In order to estimate the occupied area of each dendrimer adsorbed on gold, quartz crystal microbalance (QCM) measurement was also carried out.     

The role of exchange-correlation functionals in the potential energy surface and dynamics of N(2) dissociation on W surfaces

We study the dissociative adsorption of N(2) on W(100) and W(110) by means of density functional theory and classical dynamics. Working with a full six-dimensional adiabatic potential energy surface (PES), we find that the theoretical results of the dynamical problem strongly depend on the choice of approximate exchange-correlation functional for the determination of the PES. We consider the Perdew-Wang-91 [Perdew et al., Phys. Rev. B 46, 6671 (1992)] and Perdew-Burke-Ernzerhof (RPBE) [Hammer et al., Phys. Rev. B 59, 7413 (1999)] functionals and carry out a systematic comparison between the dynamics determined by the respective PESs. Even though it has been shown in earlier works that the RPBE may provide better values for the chemisorption energies, our study brings evidence that it gives rise to a PES with excessive repulsion far from the surface.     

Polarizable interaction potential for molecular dynamics simulations of actinoids(III) in liquid water

In this work, we have developed a polarizable classical interaction potential to study actinoids(III) in liquid water. This potential has the same analytical form as was recently used for lanthanoid(III) hydration [M. Duvail, P. Vitorge, and R. Spezia, J. Chem. Phys. 130, 104501 (2009)]. The hydration structure obtained with this potential is in good agreement with the experimentally measured ion-water distances and coordination numbers for the first half of the actinoid series. In particular, the almost linearly decreasing water-ion distance found experimentally is replicated within the calculations, in agreement with the actinoid contraction behavior. We also studied the hydration of the last part of the series, for which no structural experimental data are available, which allows us to provide some predictive insights on these ions. In particular we found that the ion-water distance decreases almost linearly across the series with a smooth decrease of coordination number from nine to eight at the end.     

Simulation analysis of contact angles and retention forces of liquid drops on inclined surfaces

A simulation study of liquid drops on inclined surfaces is performed in order to understand the evolution of drop shapes, contact angles, and retention forces with the tilt angle. The simulations are made by means of a method recently developed for dealing with contact angle hysteresis in the public-domain Surface Evolver software. The results of our simulations are highly dependent on the initial contact angle of the drop. For a drop with an initial contact angle equal to the advancing angle, we obtain results similar to those of experiments in which a drop is placed on a horizontal surface that is slowly tilted. For drops with an initial contact angle equal to the mean between the advancing and the receding contact angles, we recover previous results of finite element studies of drops on inclined surfaces. Comparison with experimental results for molten Sn-Ag-Cu on a tilted Cu substrate shows excellent agreement.     

The semiclassical determination of potential surfaces from observed spectra. I

A semiclassical method of calculating polyatomic molecular potential energy surfaces from observed vibration-rotation data is presented. It is based on EBK quantization of invariant tori and on a classical analogue of the Hellman-Feynman theorem. Applications to model potentials and the diatomics CO and I₂ compared well with other calculations.