J. Fernandez Sanz

On modelling the interaction of CO on the MgO(100) surface

Abstract In this work we discuss the interaction of an adsorbate on an ionic surface taking as representative example CO on a perfect MgO(100) surface. The main goal is to investigate the different contributions to the interaction and how to model them by using a finite cluster model. To this end we use three different ab initio Hartree-Fock approaches. First, we discuss the convergence properties of the array of point charges used to simulate the Madelung potential. Next, we use large cluster models to show that there is an oscillatory behavior of the interaction energy. We show that rather large clusters are needed to avoid such oscillations. Also, we discuss how to represent these large clusters by using model potentials and compare the results with those obtained from periodic Hartree-Fock calculations. The interaction of CO on MgO is found to be weak and of electrostatic origin, with no noticeable chemical contributions.

Induction of thyroid proliferative changes in rats treated with antithyroid compound.

This study was designed to investigate the histologic changes in goitrogen‐induced thyroid growth of the rat. The animals were orally treated by 1 % potassium perchlorate except the controls and were sacrificed in intervals ranging from 1 to 12 months.

Solvent effects on the dissociation of aliphatic carboxylic acids in water—N,N-dimethylformamide mixtures

Abstract The autoprotolysis constants of several water- N,N -dimethylformamide mixtures were determined. The acid dissociation constants of formic, acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, 2-methylbutyric and trimethylacetic acids were evaluated in the same media by potentiometric titration. Empirical equations for the calculation of autoprotolysis constants and acid dissociation constants at 25° C in the mixed solvents are proposed. Approximate solvation numbers were obtained by multiple linear regression analyses of p K a values.

Experimental and molecular dynamics simulation analysis of LaCrO3 precipitation in chromia scales

Experimental characterization of grain and grain boundaries of chromia scales upon addition of La has been carried out with a variety of techniques. The effect of lanthanum addition on the high temperature oxidation is explained based on simulations suggested by the experimental results. The grain boundary precipitation mechanism of perovskite phases suggested by our simulations is through the extraction of Cr atoms from the oxide scale.

A theoretical study of the NaTiO2 (001) rutile interaction

A theoretical study of the reduction of the TiO2 (001) rutile surface by atomic Na is reported. The study is based on ab initio embedded cluster calculations carried out for two different sites of this surface. The first one (A) is represented by a TiO4−4 cluster and the second (B), an oxygen ending site, by a cluster of formula TiO8−6. The calculations show that adsorption of Na is possible on both sites although site A is energetically favored. The electron transfer process has been examined from state averaged complete active self consistent field (CASSCF) calculations. The analysis of the these wave functions shows that the Na 3s electron is transferred to a Ti 3d orbital of the surface only on site A. For site B such a transfer would involve an excited state of the cluster. The dissociation curves for several electronic states are reported.

An iterative algorithm for consistent and unbiased estimation of linear regression parameters when there are errors in both the x and y variables

Abstract This paper describes an algorithm for unbiased estimation of regression parameters dealing with data in which the variances of both the x and y variables are different and heterocedastic. The procedure gives consistent and unbiased estimations of parameters, as well as the elements of the variance-covariance matrix.

Ab initio study of the adsorption of acetone and keto-enol equilibrium on the MgO(100) surface

Abstract An ab-initio quantum mechanical study of the adsorption of acetone and 2-propenol on a clean MgO(100) surface is reported. Ab-initio Hartree-Fock calculations have been carried out using an embedded-cluster approach in which the environment is described by total ion potentials and point charges. Optimized geometries for both acetone and 2-propenol adsorbed on the surface have been obtained using two basis sets and several model clusters. The adsorbate-surface interaction is found to be weak and electrostatic in nature, although there is a relative stabilization of the enol tautomer. The effect of the surface on the keto-enol equilibrium is analyzed and explained on the basis of this differential adsorption. Surface reconstruction induced by the adsorbate is also considered. While the surface relaxation effects are found to be negligible for acetone, they appear to be larger for 2-propenol, and allowing the surface to relax changes the qualitative description of the enolization process since in this case an enolate species is found to be adsorbed on the surface.

An ab initio study of the CH2O adsorption on the MgO (100) surface. Effects of replacing the active Mg2+ ion by different metallic cations

Abstract A theoretical analysis of the interaction between formaldehyde, CH2O, and the MgO (100) surface is reported. Ab initio Hartree-Fock calculations are carried out using an embedded cluster approach in which the environment is described by both total ion potentials and point charges. The cluster selected to describe the CH2O-surface interaction is CH2O[MgO5]8−, in which the formaldehyde oxygen is coordinated to the Mg2+ ion. The effect of the addition of metallic cations to the catalyst is analysed by replacing the cluster Mg2+ ion by Na+, Al3+, Sc3+ and Ti4+ so as to modify the Lewis acid properties of the surface. The different contributions to the adsorbate-surface interaction are analysed, and the theoretical vibrational frequencies are discussed.

Ab initio calculation of the electronic coupling element in bimetallic model compounds [MLM]+, M = Be, Mg, Zn; L = O, S, CH2, CC; electron correlation effects and dependence on the bridge nature

Ab initio calculations of the electron-transfer matrix element Vab in bimetallic model systems [MM]+ and [MLM]+ with M = Be, Zn and L = O, S, CH2 and CC, are reported. Electron correlation effects are estimated through a second-order method in which only the differential space contributing to the transfer integral Hab is considered. Vab is found to be noticeably larger for bridged systems, showing that the through bond mechanism is pre-eminent in these systems. In most of the calculations, electron correlation contributions are found to increase Vab, the corrections in some cases being as large as 35%. Analysis of the second-order contributions in these cases shows that intruder states involving ligand or metal ligand excitations strongly mix with the zeroth-order model wave functions.

Cell Types in the Main Excretory Duct of the Submaxillary Gland of the Rat

This work is an ultrastructural study of the cells of the excretory duct epithelium of the submaxillary gland of the rat. This epithelium undergoes progressive loss of cytoplasm which leads to the presence of three distinct types of cell.