The shielding of external electric fields in atoms revisited

An atom, placed in an external homogeneous field, will show a complex charge distribution. The pattern of the polarization density distribution, obtained by subtracting the original electron from the one of the polarized atom, can easily be explained by considering the various orbitals. Poisson's equation relates the induced field to polarization density distribution

The molecular electron density distribution meeting place of X-ray diffraction and quantum chemistry intermediate - between theory and experiment

Quantum chemistry and the concepts used daily in chemistry are increasingly growing apart. Among the concepts that are able to bridge the gap between theory and experimental practice, electron density distribution has an important place. The study of this distribution has led to new developments in theory, including Hellmann-Feynman theory and the density functional theory. The possibilities and limitations of these methods are discussed. Various ways of analysing the electron density distribution are presented and discussed. X-ray diffraction enables us to ¿observe¿ the electron density distribution and electrostatic properties. Experimental results are compared with the results of quantum chemical calculations. It is shown that even intermolecular interaction is observable with this method. Problems in determining ionic charges are seen to be inherent in the method

Electrostatic Molecular Interaction from X-ray Diffraction Data. II. Test on Theoretical Pyrazine Data

In a previous paper [Moss & Feil (1981). Acta Cryst. A37, 414-421] a method was reported to calculate the electrostatic potential and the electrostatic interaction energy from single-crystal X-ray diffraction data. The method was applied to experimental pyrazine data; however, owing to the relatively low quality of the data, the results were inconclusive. In the present paper the results are presented of a model study in which the method has been applied to the analysis of ideal error-free diffraction data calculated from a theoretical wavefunction. The molecular quadrupole moments and the electrostatic interaction energies of two pyrazine molecules thus obtained are in very good agreement with the corresponding results derived directly from the wavefunction. Thus the proposed method may be used to determine the long-range electrostatic component of molecular interactions from highly accurate X-ray diffraction data

The electron density distribution in CN−, LiCN and LiNC. The use of minimal and extended basis set SCF calculations

Electron density maps are reported for the CN−ion and the LiCN and LiNC molecules, calculated from molecular wave-functions near the Hartree-Fock limit. The electron density distribution derived from CNDO/ 2 wavefunctions does not resemble the ab initio results. The ultimate ability of a minimal basis set to represent the electron density near the Hartree-Fock limit, has been tested. The requirement of N-representability of the trial electron density has been satisfied. It is found that the molecular valence density cannot be reproduced to a satisfactory extent by a minimal set of Slater orbitals, even when the exponents of the basis orbitals are optimized

Funding public health care: A flat-rate premium might be bad for employment

If "tax progression is good for employment in popular models of trade union behaviour" (Koskela and Vilmunen, 1996), then a flat-rate premium, as proposed as a means of funding for public health care, is bad. This note shows that replacing existing (proportional) social security contributions by a lump-sum payment increases labour costs and thus reduces employment. This result holds - for empirically relevant parameters - even in a more general case than the one considered by Koskela and Vilmunen. Policy advisers should be aware that in imperfect competitive labour markets the prima facie attractiveness of a flat-rate premium is not for sure.

Uncoupled Hartree-Fock calculations of the polarizability and hyperpolarizabilities of nitrophenols

The polarizability and hyperpolarizabilities of nitrophenols as model compounds for studying nonlinear optics have been investigated at the Hartree-Fock level of approximation by means of the Dalgarno Uncoupled Hartree-Fock (DUHF) or Sum Over Orbitals (SOO) method. The additive character and the charge transfer effects in α,β,γ and have been analyzed in terms of the δ and π molecular orbital contributions, the contribution of the individual π molecular orbitals, and the contribution of the highest occupied and the lowest unoccupied\ud molecular orbitals. Within the SOO approach, the reliability of the Two-Level Model has been tested and the influence of the rotation of the nitro group and of the presence of the intramolecular hydrogen bonding in ortho-nitrophenol have been studied. The results show that the present method is a reliable and efficient tool for the prediction of trends in the molecular polarizability and hyperpolarizabilities of large molecule

The crystal structure of thiourea nitrate

The structure of thiourea nitrate has been determined by three-dimensional X-ray methods. Both Cu Ke and Mo K~ data were obtained with a single-crystal diffractometer and the final R values are 4.9% and 5.5% respectively. The space group is P211m and there are two molecules in the unit cell. All atoms, including hydrogen, lie on mirror planes. The whole structure is built up of layers of atoms, the atoms within each layer being linked by a network of hydrogen bonds

Heterogeneous labour markets in a microsimulation-AGE model : application to welfare reform in Germany

"Labour market reforms that are designed to stimulate labour supply at the lower end of the wage distribution can never be precisely restricted to affect only the target group. Spillovers to and feedback from other segments of the labour market are unavoidable and may counteract the direct effects of the reform. An adequate representation of heterogeneous labour markets becomes therefore an important issue for the assessment of reforms. We analyse the possible interactions between labour market segments in a combined, consistent microsimulation-AGE model with a flexible representation of substitution possibilities and different wage-forming regimes. We look at a stylised reform and find labour-demand cross-price elasticities between the low and medium skilled to be the main drivers of the results. Interaction with the high-skilled segment is less pronounced." (Author's abstract, IAB-Doku) ((en))Niedrigqualifizierte, mittlere Qualifikation, Hochqualifizierte, Lohnfindung, Anreizsystem, Leistungskürzung, Arbeitslose, aktivierende Arbeitsmarktpolitik - Auswirkungen, Beschäftigungseffekte, Erwerbsverhalten, Arbeitskräfteangebot, Lohnhöhe, Einkommensverteilung, Bruttoinlandsprodukt, öffentliche Einnahmen, Konsum, Investitionen, Kapitalmobilität, Arbeitsmarktmodell, Heterogenität

Heterogeneous labour markets in a microsimulation-AGE model: application to welfare reform in Germany

Labour market reforms that are designed to stimulate labour supply at the lower end of the wage distribution can never be precisely restricted to affect only the target group. Spillovers to and feedback from other segments of the labour market are unavoidable and may counteract the direct effects of the reform. An adequate representation of heterogeneous labour markets becomes therefore an important issue for the assessment of reforms. We analyse the possible interactions between labour market segments in a combined, consistent microsimulation-AGE model with a flexible representation of substitution possibilities and different wage-forming regimes. We look at a stylised reform and find labour-demand cross-price elasticities between the low and medium skilled to be the main drivers of the results. Interaction with the high-skilled segment is less pronounced. --Applied general equilibrium model,microsimulation,discrete working time choice,heterogeneous labour markets,labour market reform

The electron density distribution in the hydrogen bond. A quantum chemical and crystallographic study

With the help of Hartree—Fock—Slater calculations in which very large basis sets are employed, the polarisation of the water molecule by an electric field is explored. The various features in the electron density distribution are encountered again in the long hydrogen bond in the water dimer, showing that polarisation is the main effect. In short hydrogen bonds, exchange repulsion is shown to be equally important.\ud \ud The quality of the computational method is tested by comparing the results of the calculation of the electron density distribution in the crystal of α-oxalic acid dihydrate with the results of accurate X-ray diffraction measurements. By using models in which subsequently covalent bonding, hydrogen bonding and the electrostatic crystalline field are included, the effects of the various components are explored. Only the full theoretical model gives excellent agreement with the experiment, showing the quality of the model and the sensitivity of the experiment