Computer simulation of chemisorption on strained metals

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The general nature of the adsorption influence of environments on the mechanical properties of the metals is extensively studied both in practice and theoretically [1]. In the theoretical analysis, the application of quantumchemical methods enables one to reproduce a clear unambiguous picture of interatomic interactions in terms of the theory of electronic structure on the basis of the results of computer simulations [2]. The analysis of interaction of metals with gaseous hydrogen is especially important for the solution of various problems in materials science.Earlier, we successfully used the semiempirical quantum-chemical cluster methods for the evaluation of the influence of the level of strains in metals on the energy and geometric parameters of the adsorption of atoms and molecules of simple gases, including hydrogen [3]. However, the investigation of the problem only for some metals cannot be regarded as a well-justified basis for making the conclusion concerning the general nature of activation of the surface interactions in the process of deformation of the crystal lattice.For this reason, in the present work, we consider a much larger number of metals from the periodic table interacting with hydrogen. For numerical computations, we use a more accurate (from the theoretical point of view) nonempirical ab initio method in the unrestricted Hartree-Fock approximation (UHF) with STO-G3 basis orbitals (Slater-type orbitals--3 Gaussians) [4]. It is worth noting that the semiempirical methods are parametrized only for several elements excluding, in fact, transition metals. All numerical computations were carried out on a Pentium-166 personal computer by using the GAMESS software package [5]. Cluster Model of Interaction of Molecular Hydrogen with MetalsFor the numerical simulation of metal clusters, we take elementary cells depicted in Fig. 1. An atom of hydrogen is adsorbed on the (100) face for metals with bcc or fcc lattice and on the (1000) face for metals with hexagonal lattice. In these cases, the heats of adsorption take their maximum values. Results of Numerical Calculations and Their AnalysisAs shown in [3,6], the multicoordination positions are characterized by the maximum heats of adsorption of hydrogen. This observation is confirmed by the rigorous nonempirical approach. On the (100) face (for metals with cubic lattice) and (1000) face (for metals with hexagonal lattice), the roles of these positions are played by 4-and 3-coordination positions, respectively (see Fig. 1). The difference between the values of the heat of adsorption on the three nearest low-index (100), (110), and (111) faces is insignificant (5-7%). For this reason, the choice of the (100) face as basic enables us to reveal the regularities of changes in the energy and geometric parameters of adsorption depending on the nature of the metal. In addition, for the major part of metals, the heat of adsorption of hydrogen is maximum on this face. Moreover, the structure of the cluster with absorption on this face enables one to simulate s...

“…As shown in [3,6], the multicoordination positions are characterized by the maximum heats of adsorption of hydrogen. This observation is confirmed by the rigorous nonempirical approach.…”

Section: Results Of Numerical Calculations and Their Analysismentioning

confidence: 99%

Section: Influence Of Strainsmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

See 2 more Smart Citations

Heats of adsorption of hydrogen on metals

Kopylets¹

1999

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“…Our analysis of the effect of elastic deformation on the adsorption energy and structure of surface complexes, performed by quantum-chemical semiempirical cluster methods, revealed significant activation of the chemisorption process [3,4]. However, the accumulation of experimental data on the energetics of adsorption on deformed oriented metallic single crystals requires precise experiments and is rather complicated.…”

Section: Introductionmentioning

confidence: 94%

Quantum-chemical simulation of selective dissolution of brass and zinc-aluminum alloy

Pokhmurs'kyi¹,

Kopylets²,

Kornii³

1998

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Vibration spectra of molecules adsorbed on deformed metals

Kopylets¹

1998

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A quantum-chemical cluster model for calculating the vibration spectra of water and hydrogen sulfide molecules adsorbed on nickel and copper is developed and substantiated. The effect of noticeable shifts of the major vibration peaks during deformation of metals is demonstrated.The universality of the phenomenon of the adsorptive effect of a medium on the mechanical properties of solids (the Rebinder effect) and its fundamental importance in solving practical problems made it necessary to thoroughly study its nature.From the standpoint of thermodynamics, this effect is caused by a decrease in the interfacial surface energy at a solid-medium interface [ 1 ]. On the other hand, real patterns of deformation and breakdown of the lattice of a solid, nucleation and propagation of cracks with the participation of surface-active particles of the medium were reproduced by the method of molecular dynamics [3] with the use of a detailed numerical analysis at the atomic-molecular level. However, the application of the concepts of molecular mechanics with complete replacement of the complex energy interaction by simple interatomic potentials does not allow one to consider, in this method and in similar ones, the chemical character of the influence of adsorbed particles and the surface of the solid on the structure and strength of bonds between them.By employing the quantum-chemical semiempirical cluster methods, we calculated the effect of elastic deformation on the adsorption energy and structure of surface complexes. This enabled us to establish significant activation of the chemisorption process [3,4]. However, the obtained results, despite a satisfactory qualitative agreement with experimental data, do not offer a detailed quantitative explanation of the real dynamics of surface phenomena occurring in mechanical force fields. Therefore, taking quantum-chemical cluster calculations as a base, we must study the dynamic characteristics of particles chemisorbed on the surface of a solid under deformation of the crystalline lattice. Among these characteristics, vibration spectra of simple molecules are the most available.To simulate vibrations, we chose the following simple chemisorption systems: water and hydrogen sulfide molecules on nickel and copper clusters. Calculations were performed with an IBM 486 DX4-100 personal computer by a specially parametrized (for obtaining spectra) semiempirical method ZINDO/S [5]. Clusters were composed of 2, 4, and 11 atoms of the metal, which simulate the surface (111) (Fig. 1). Since a change in the electronic structure is rather local during chemisorption, the calculation of small clusters reproduces it rather adequately [6]. A quantum-chemical approach is expedient when the major characteristics of the vibration spectrum can be obtained for small clusters. Then details can be refined in calculations with large clusters. Here, we deal with actually short-range chemical forces. Preliminary calculations of an equilibrium geometry were performed for simple systems (Table 1). Both molecules ...