(Pdf) metal dissolution in aqueous electrolyte semi-empirical hartree-fock and ab initio md calculations gasbuddy

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The results of electronic structure calculations for different terminations of SrTiO3 (100) and (110) perovskite gas oil ratio thin films are discussed. These calculations are based on the ab initio Hartree-Fock (HF) me- thod and Density Functional Theory (DFT). Results are compared with previous ab initio plane-wave LDA and classical Shell Model (SM) calculations. Calculated considerable increase of the Ti – O chemical bond covalency nearby the surface is confirmed by experimental data. Our quantum chemical calculations performed by means of the intermediate neglect of differential overlap (INDO) method confirm the exis- tence of self-trapped electrons in KNbO3, KTaO3 and BaTiO3 crystals. The relevant lattice relaxation en- ergies are 0.21 eV, 0.27 eV and 0.24 eV, and the optical absorption energies 0.78 eV, 0.75 eV and 0.69 eV, respectively. We suggest a theoretical interpretation of the so-called green luminescence (2.2 – 2.3 eV) in ABO3 perovskite crystals as a result of the recombination of electrons and holes forming the Charge – Transfer-Vibronic-Exciton (CTVE). The calculated luminescence energies for SrTiO3, BaTiO3, KNbO3 and KTaO3 perovskite crystals are in a good agreement with the experimentally observed energies.

We have used the classical molecular dynamics technique to simulate the ordering of a water film adsorbed on an atomic model of a tip of a scanning tunneling microscope approaching a planar metal surface. For this purpose, we have developed a classical model for the water–substrate interactions that solely depends on the coordinates of the particles and electricity transmission efficiency does not require the definition of geometrically smooth boundary surfaces or image planes. The model includes both an electrostatic induction for the metal atoms (determined by means of an extended Lagrangian technique) and a site‐specific treatment of the water–metal chemisorption. As a validation of the model we have investigated the structure of water monolayers on metal substrates of various topology [the (111), (110), and (100) crystallographic faces] and composition (Pt, Ag, Cu, and Ni), and compared the results to experiments. The modeling of the electrostatic induction is compatible with a finite external potential imposed on the metal. This feature is used to investigate the structural rearrangements of the water bilayer between the pair of scanning tunneling microscope electrodes in response to an applied external voltage difference. We find significant asymmetry in the dependence on the sign of the applied voltage. Another result of the calculation is an estimate of the perturbation to the work gas prices going up or down function caused by the wetting film. For the conditions typical for operation of a scanning tunneling microscope probe, the change in the work function is found to be comparable to the applied voltage (a few hundred millivolts). © 1995 American Institute of Physics.

The adsorption of Cl-, Br- and I- anions on cluster models of the Ag(100) and the Pt(100) surfaces has been studied by means of ab initio wavefunctions. Potential energy curves have been determined for various adsorption sites, allowing a direct comparison of the adsorption properties of silver and platinum surfaces. The bonding mechanism has been analysed in detail by means of a technique which allows one to decompose the interaction energy into the sum of various contributions. Three dominant mechanisms contribute to determine the adsorption energy: the Pauli or exchange repulsion, the metal polarization, and the partial dative bonding from the anion to the surface. On Ag clusters the trend in stability of the various adsorption sites, bridge four-fold hollow top, closely follows the order electricity prices over time of polarizability of the sites. On Pt, the preferred site is determined by the Pauli repulsion more than by the substrate polarization, providing an indication of the importance of relativistic effects in Pt. Copyright (C) 1996 Elsevier Science Ltd

The adsorption of water and hydroxyl on the (111) surface of Ni is treated using a many-electron embedding theory to describe the electronic bonding, modelling the lattice as a 28-atom, three layer cluster. Ab initio valence orbital configuration interaction (multiple parent) calculations carried out on a local surface region permit an accurate description of bonding at the surface. Molecular H2O adsorbed on the Ni(111) surface is found to prefer an atop atom site with an adsorption energy of 12 kcal/mol and a Ni-O equilibrium distance of 2.06 Å. The equilibrium geometry of H2O is calculated to lie in a plane inclined by about 25° to the normal to the surface, but tilting the plane of the molecule from 0° to 50° or rotating the molecule about the Ni-O axis changes the energy only slightly. The OH radical binds strongly to the Ni(111) surface at both three-fold and bridge sites with adsorption energies of 87 kcal/mol and Ni-O bond lengths from 2.02–2.08 Å. The OH axis of adsorbed OH is inclined about 10° from the surface normal at a three-fold site. Dissociation of H2O to OH and H adsorbed at nearby three-fold sites is exothermic, and for OH and H at a large distance of separation, the reaction H2O(ads) α OH(ads) + H(ads) is 52 kcal/mol exothermic. A high energy barrier is found at the initial stage of dissociation. The work function decreases by ∽0.5 eV on H2O online electricity bill payment adsorption and increases by ~0.2 eV on OH adsorption.

We studied the charge and potential distribution near the (100) GaP surfaces which bear the characteristic features common to polar surfaces of semiconductors. A self-consistent periodic quantum-chemical technique and a slab model are employed and the atomic and electronic structures for several surface stoichiometries are calculated. We compare these results with the predictions of the model approaches in order to check the limits of applicability of simplified models such as the electron-hole counting model or the model suggested by Nosker, Mark and Levine. We have found that zero dipole moment of the slab is an important criterion of the surface stability. The charges of the surface ions are flexible in our model and decrease strongly at the surface with respect to the bulk values j gastroenterol. Therefore this criterion does not impose such severe restrictions on the surface stoichiometry, composition, and structure as are suggested in other models. We conclude that structure and stability of polar surfaces are determined by a balance of stoichiometric factors and electron density redistribution which should both be taken into account in a self-consistent manner.

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 … [Show full abstract] corresponds to water donating a hydrogen bond to the C center. The MM-calculated surface it 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 electricity worksheets grade 6 radius of the C atom. The calculated Gibbs energy of hydration is in good agreement with experiment (9.3 kJ/mol calc. vs 10.7 kJ/mol exptl.). The calculated diffusivity of CO(aq) in TIP3P-model water was 5.19 x 10-5 cm2/s calc., more than double the experimental value of 2.32 x 10-5 cm2/s Read more

Genetic algorithm is employed to survey an empirical potential energy surface for small NaxKy clusters with x + y ≤ 15, providing initial conditions for electronic structure methods. The minima of such empirical potential are assessed and corrected using high level ab initio methods such as CCSD(T), CR-CCSD(T)-L and MP2, and benchmark results are obtained for specific cases. The results are the … [Show full abstract] first calculations for such small alloy clusters and may serve as a reference for further studies. The validity and choice of a proper functional and basis set for DFT gas to liquid calculations are then explored using the benchmark data, where it was found that the usual DFT approach may fail to provide the correct qualitative result for specific systems. The best general agreement to the benchmark calculations is achieved with def2-TZVPP basis set with SVWN5 functional, although the LANL2DZ basis set (with effective core potential) and SVWN5 functional provided the most cost-effective results. Read more

This contribution is devoted to the impact of density functional theory in the most important building blocks of a comprehensive theoretical characterization and analysis of processes involving open-shell species. After a discussion of the theoretical background, I report the essentials of a number of case studies selected to show the potentialities and limits of local and gradient corrected … [Show full abstract] density functionals in dealing with structural, spectroscopic, thermochemical and kinetic aspects. At the same time I introduce self-consistent hybrid methods obtained by adding some Hartree–Fock exchange to gradient-corrected functionals. The results hp electricity bill payment online obtained at this level for a number of properties are competitive with the most sophisticated post-Hartree–Fock approaches. The speed of the computations and the availability of analytical first and second derivatives allow the complete characterization of stationary points and the analysis of significant regions of potential energy surfaces for systems much larger than those which can be dealt with by conventional ab-initio methods. This paves the route toward the study of large amplitude motions, from conformational transitions to true chemical reactions. Read more Discover more