Perspective on "Self-consistent molecular Hartree-Flock-Slater calculations", Baerends,EJ, Ellis,de, Ros,P (1973) Chem Phys 2:41

This paper discusses the title paper by Baerends, Ellis, and Ros. We show the role it has played in the development of density functional theory and the further work it has initiated

Psychological contract development: An integration of existing knowledge to form a temporal model

The psychological contract has received substantial theoretical attention over the past two decades as a popular framework within which to examine contemporary employment relationships. Previous research mostly examines breach and violation of the psychological contract and its impact on employee organization outcomes. Few studies have employed longitudinal, prospective research designs to investigate the psychological contract and as a result, psychological contract content and formation are incompletely understood. It is argued that employment relationships may be better proactively managed with greater understanding of formation and changes in the psychological contract. We examine existing psychological contract literature to identify five key factors proposed to contribute to the formation of psychological contracts. We extend the current research by integrating these factors for the first time into a temporal model of psychological contract development

An Ab Initio embedded cluster study of the adsorption of NH3 and NH4+ in chabazite

The adsorption of NH3 in acidic zeolites has been studied extensively experimentally. Therefore, it can be used very well to verify a model used in a quantum chemical calculation. Here, we present a calculation that, from a quantum chemical point of view, should give a reliable description of the adsorption process. We studied the adsorption of NH3 and NH4+ in chabazite with the embedded cluster method using a reasonable basis set, applying the counterpoise correction and including electron correlation. The geometry was partially optimized. With this calculation we verified the reliability of our model and obtained information that cannot be obtained experimentally. The adsorption energies of hydrogen-bonding NH3 and of NH4+ were -70 +/- 10 kJ/mol and -120 +/- 15 kJ/mol, respectively. The latter value compares very well with the experimental heat of adsorption. NH4+ has a high coordination with the zeolite wall; this is confirmed experimentally. A good geometry is obtained if the boundary of the embedded cluster is kept fixed to that of the zeolite crysta

The quantum-chemical basis of the catalytic reactivity of transition-metals

State of the art computational quantum-chemical methods enable the modelling of catalytically active sites with an accuracy of relevance to chemical predictability. This opens the possibility to predict reaction paths of elementary reaction steps on catalytically active surfaces. The results of such an approach are illustrated for a few dissociation and association reactions as they occur on transition metal surfaces. Examples to be given concern CO dissociation. carbon-carbon coupling and NH3 oxidation. Reaction paths appear to be controlled by the principle of minimum surface atom sharin

Electronic structure calculations and dynamics of methane activation on nickel and cobalt

The dissociative chemisorption of CH4 on nickel and cobalt has been studied using different cluster models. D. functional theory is used to det. the structure and potential energy surface in the reactant-, transition state-, and product region. The transition state is explicitly detd. on a single atom, a one layer 7-atom cluster and a spherical 13-atom cluster. We find transition state barriers of 41 kJ/mol for a single nickel atom, 79 kJ/mol for a single cobalt atom, 214 kJ/mol for the Ni7-cluster, 216 kJ/mol for the Co7-cluster, 121 kJ/mol for the Ni13-cluster, and 110 kJ/mol for the Co13-cluster. The overall reaction energies are -34, 6, 142, 135, 30, and 8 kJ/mol, resp. The higher barrier for the single cobalt atom in comparison with the nickel atom can be attributed to the difference between both atoms in the occupation of the s-orbital in the lowest lying states. The higher and almost the same barrier for the 7-atom clusters can be attributed to the intrinsic lower reactivity of the central atom embedded in the cluster and the similar electronic nature of the atoms in the clusters; in both clusters the atoms have open s- and d-shells. The lower barrier for the 13-atom clusters compared with the 7-atom clusters is a result of each surface atom now having 5 bonds, which gives a more balanced description of the substrate model. [on SciFinder (R)

Interatomic potentials for zeolites. Derivation of an ab-initio shell model potential

A new method has been developed for deriving parameters for the shell model of silica polymorphs. All parameters for the shell model are derived in a self-consistent way from ab-initio potential energy surfaces, polarizabilities, and dipole moments of small clusters. This yields an ab-initio partial-charge-shell model potentia

Ab initio density-functional theory study of NHx dehydrogenation and reverse reactions on the Rh(1111) surface

The adsorption and dissociation of NHx fragments on the Rh(111) crystal surface have been studied using first-principles density-functional calculations. The stability and configurations of NHx species have been investigated and characterized using frequency analysis. The highest adsorption energies have been calculated for NH and N. Several paths of NHx (x=1–3) dehydrogenation and hydrogenation have been taken into account. The transition states have been determined and in detail analyzed. The activation barriers and thermodynamic and kinetic data have been calculated for all the elementary steps. The calculations have shown that the elementary reactions have significant barriers, between 0.7 and 1.1 eV. The transition states are regarded neither early nor late with respect to the distance in hyperspace between initial and final states. The NH3 dehydrogenation has been determined as the rate limiting step. For this elementary process there has been estimated a large contribution of the zero point energy to the activation barrier and a significant entropy activation

Density functional theory calculations of the transition states for hydrogen exchange and dehydrogenation of methane by a Brönsted zeolitic proton

D. functional and semiempirical (MNDO) theories are used to det. transition states and the corresponding activation barriers of hydrogen exchange and dehydrogenation of methane catalyzed by a protonated zeolite cluster model. The nonlocal d. functional activation barriers were found to be 125 and 343 kJ/mol for hydrogen exchange and dehydrogenation, resp. From the imaginary frequency of one of the transition state Eigen modes, the reaction coordinates were deduced. Addnl., from the activation barrier and vibration, rotation, and translation partition functions, reaction rate consts. have been evaluated using transition state reaction rate theory. [on SciFinder (R)

Spectroscopy, energetics and siting of NH+4 in zeolites; theory and experiment

The adsorption of an NH3 mol. on an acidic zeolite and the proton transfer from the zeolite to the NH3 are studied by quantum chem. methods. The NH+4 is adsorbed with 2 or 3 H bonds to the zeolite. The calcd. vibrational frequencies explain the exptl. IR spectra. [on SciFinder (R)

Fluorite transition metal hydride induced destabilization of the MgH2 system in MgH2/TMH2 multilayers (TM=Sc, Ti, V, Cr, Y, Zr, Nb, La, Hf)

The structural changes in MgH2 induced by contact with fluorite transition metal hydrides (TMH2, TM=Sc, Ti, V, Cr, Y, Zr, Nb, La, Hf) have been studied using density-functional theory calculations. Models of MgH2(rutile)/TiH2(fluorite) and MgH2(fluorite)/TiH2(fluorite) multilayers with different Mg:TM ratios have been designed. With a fixed thickness of the TMH2 layer, structure transformation of MgH2 from rutile to fluorite occurs with a decrease in thickness of the MgH2 layer. The hydrogen desorption energy from the fluorite MgH2 layer in the multilayers is significantly lower than that of the bulk rutile MgH2. The structural deformation of the MgH2 layer due to the strain induced by TMH2 is found to be responsible for the destabilization of the Mg-H bond: the more structural deformation, the more destabilization of the Mg-H. Our results provide an important insight for the development of new hydrogen-storage materials with desirable thermodynamic properties