Oxygen diffusion through the Ag(111) surface: A quantum chemical study by the NDDO/MC method

Atomic forms of oxygen on the (111) face of metallic silver are studied by the NDDO/MC semiempirical method. The surface (above the octahedral void) and subsurface (within the void) positions of oxygen between the first and second layers of the (111) face are investigated. The potential surface cross section is calculated for the subsurface position of oxygen. A new approach is used to take into account surface relaxation due to reaction with adsorbate. The barrier of atomic oxygen diffusion through the surface is much lower than the banier of its desorption from the surface. The correlation correction to the diffusion and desoption barrier energies is estimated by the double CI (DCIP) method. The greatest correlation effects are obtained in the desorption banier calculation. Translated fromZhumal Stmktunoi Khimii, Vol. 41, No. 2, pp. 248-254, March–April, 2000.     

Scaling the Coulomb interaction in calculations of electron spectra of transition metal complexes

A simple technique of scaling two-electron integrals in ab initio calculations of the electronically excited states of transition metal complexes is proposed. This technique uses the fact that one-center two-electron integrals depend linearly on the scaling factor when Slater type functions are subjected to scaling transformation. This leads to a linear dependence of the d—d transition energy on the “scale” of Coulomb interaction, which allows one to affect the calculation result by varying the Slater exponential. To test the technique, ab initio configuration interaction and full active space calculations of the low excited states of the CrF ₆ ^3- , MnF ₆ ^2- , and VF ₆ ^3- complexes are performed. For transition elements, a basis of Slater type effective functions chosen from the optical spectra of the atoms and ions of transition elements is used. It is shown that in the STO-6G basis with effective exponentials, experimental transitions are reproduced with an accuracy of about 2000 cm^-1 even with the use of small active space determined by the orbitals localized on the central atom of the complex.     

NDDO/MC: A new semiempirical SCFMO method for transition metal complexes

A new semiempirical SCF MO procedure available for prediction of the transition-metal complexes' binding energy and molecular geometry is developed. The features of the method are (i) an explicit account of the orthogonality of the basis set; (ii) use of a new formula for the resonance integral; and (iii) an effective account of the Coulomb correlation of electrons in the calculation of the two-electron integrals based on approach of a model Coulomb hole function. The parameterization for H, C, N, O, Co, and Ni atoms is presented. The results of NDDO /MC (NDDO for Metal Compounds) calculations of molecular geometries and binding energies for a number of organic compounds and more than 30 cobalt and nickel complexes are compared with the available experimental and ab initio data. The average absolute errors for the binding energies of organic molecules and metal complexes are 8.8 and 5.0 kcal/mol, respectively. © 1992 John Wiley & Sons, Inc.     

Numerical investigation of natural and forced solutal convection above the surface of a growing crystal

Numerical simulation of the solution dynamics (natural and forced convection) above the surface of growing aqueous-soluble KDP crystals is carried out. A flow of supersaturated solution falling on the crystal surface through the multi-nozzle feeder is considered. An effective method based on time-dependent Navier–Stokes and energy equations in Boussinesq approximation has been developed for numerical investigation. Parametrical calculations of different regimes of hydrodynamics and mass transfer in a crystallization chamber are performed. Some important quantitative characteristics for high-rate growth technology development are obtained.     

Daubechies wavelets as a basis set for density functional pseudopotential calculations

Daubechies wavelets are a powerful systematic basis set for electronic structure calculations because they are orthogonal and localized both in real and Fourier space. We describe in detail how this basis set can be used to obtain a highly efficient and accurate method for density functional electronic structure calculations. An implementation of this method is available in the ABINIT free software package. This code shows high systematic convergence properties, very good performances, and an excellent efficiency for parallel calculations.     

Closed and open-shell atomic oxygen on silver: two distinct patterns of the O<Subscript>1s</Subscript> binding energy and X-ray absorption O <Emphasis Type="Italic">K</Emphasis>-edge spectra as revealed by density functional theory

The electronic structure of atomic oxygen adsorbed species is studied by means of the density functional theory in the context of the ethylene epoxidation on the silver surface. The adsorbed oxygen species are modeled by the Ag₂O molecule either in its closed (¹A₁) or open-shell states (³B₁ and ¹B₁). In both open-shell states the 1s level appears to be lower than that in ¹A₁ by about 2 eV. This is apparently a sequence of the separation of electron pair, occupying the *-type highest occupied molecular orbital (HOMO), decreasing the electron density at the oxygen center. Such variation of the O_1s level for closed and open-shell Ag₂O states seems to explain the X-ray photoelectron spectroscopy (XPS) data concerning two distinct atomic oxygen species on silver surface having the O_1s binding energy of about 528 and 530 eV, called nucleophilic and electrophilic oxygen, respectively. The X-ray absorption O K-edge spectra (XANES) calculated for two types of the Ag₂O states by means of multiple-scattered-X-based approach appears to be in a qualitative agreement with those experimentally recorded for nucleophilic and electrophilic oxygen.     

Charge sensing amplification via weak values measurement

A protocol employing weak values (WVs) to obtain ultrasensitive amplification of weak signals in the context of a solid-state setup is proposed. We consider an Aharonov-Bohm interferometer where both the orbital and the spin degrees of freedom are weakly affected by the presence of an external charge to be detected. The interplay between the spin and the orbital WVs leads to a significant amplification even in the presence of finite temperature, voltage, and external noise.     

Structure and Properties of Exotic Nano- and Mesodiamonds with Pentagonal Symmetry

Russian Physics Journal - A comprehensive critical survey of structures of exotic nano-, meso- and microdiamonds with dodecahedral and icosahedral symmetry (N/MDPS) is presented. Due to their high...