Exchange and correlation energy functionals for two-dimensional open-shell systems

We consider density functionals for exchange and correlation energies in two-dimensional systems. The functionals are constructed by making use of exact constraints for the angular averages of the corresponding exchange and correlation holes, respectively, and assuming proportionality between their characteristic sizes. The electron current and spin are explicitly taken into account, so that the resulting functionals are suitable to deal with systems exhibiting orbital currents and/or spin polarization. Our numerical results show that in finite systems the proposed functionals outperform the standard two-dimensional local spin-density approximation, still performing well also in the important limit of the homogeneous two-dimensional electron gas

Energy lowering of current-carrying single-particle states in open-shell atoms due to an exchange-correlation vector potential

Current-density-functional theory is used to perturbatively calculate single-particle energies of open-shell atoms prepared in a current-carrying state. We focus on the highest occupied such energy, because its negative is, in principle, the exact ionization energy. A variety of different density functionals and calculational schemes are compared with each other and experiment. When the atom is prepared in a current-carrying state, a current-dependent exchange-correlation functional is found to slightly lower the single-particle energy of the current-carrying orbital, as compared to a calculation using standard (current independent) density functionals for the same system. The current-dependent terms in the exchange-correlation functional thus provide additional stabilization of the current-carrying state.Comment: 13 pages, accepted by Int. J. Quantum Che

Assessment of density functional approximations for the hemibonded structure of water dimer radical cation

Due to the severe self-interaction errors associated with some density functional approximations, conventional density functionals often fail to dissociate the hemibonded structure of water dimer radical cation (H2O)2+ into the correct fragments: H2O and H2O+. Consequently, the binding energy of the hemibonded structure (H2O)2+ is not well-defined. For a comprehensive comparison of different functionals for this system, we propose three criteria: (i) The binding energies, (ii) the relative energies between the conformers of the water dimer radical cation, and (iii) the dissociation curves predicted by different functionals. The long-range corrected (LC) double-hybrid functional, omegaB97X-2(LP) [J.-D. Chai and M. Head-Gordon, J. Chem. Phys., 2009, 131, 174105.], is shown to perform reasonably well based on these three criteria. Reasons that LC hybrid functionals generally work better than conventional density functionals for hemibonded systems are also explained in this work.Comment: 10 pages, 5 figures, 4 table

Stretched chemical bonds in Si6H6: A transition from ring currents to localized pi-electrons?

Motivated by solid-state studies on the cleavage force in Si, and the consequent stretching of chemical bonds, we here study bond stretching in the, as yet unsynthesized, free space molecule Si6H6. We address the question as to whether substantial bond stretching (but constrained to uniform scaling on all bonds) can result in a transition from ring current behaviour, characteristic say of benzene at its equilibrium geometry, to localized pi-electrons on Si atoms. Some calculations are also recorded on dissociation into 6 SiH radicals. While the main studies have been carried out by unrestricted Hartree-Fock (HF) theory, the influence of electron correlation has been examined using two forms of density functional theory. Planar Si6H6 treated by HF is bound to be unstable, not all vibrational frequencies being real. Some buckling is then allowed, which results in real frequencies and stability. Evidence is then provided that the non-planar structure, as the Si-Si distance is increased, exhibits pi-electron localization in the range 1.2-1.5 times the equilibrium distance

Exchange and correlation as a functional of the local density of states

A functional $E_{xc}[\rho(\r,\epsilon)]$ is presented, in which the exchange and correlation energy of an electron gas depends on the local density of occupied states. A simple local parametrization scheme is proposed, entirely from first principles, based on the decomposition of the exchange-correlation hole in scattering states of different relative energies. In its practical Kohn-Sham-like form, the single-electron orbitals become the independent variables, and an explicit formula for the functional derivative is obtained.Comment: 5 pages. Expanded version. Will appear in Phys. Rev.

The Subjectivation of Work and Established-Outsider Figurations

This paper deals with the unintended consequences of new management strategies, i.e. the internalisation of markets and the subjectivation of work, on social relations in the workplace. Through the example of two organizational case studies from care services and public transport, it is shown that these managerial strategies foster social fragmentation; specifically, the emergence of established-outsider figurations in the workplace. The paper highlights third parties as an important intervening actor in established-outsider figurations at the organizational level. Third parties, e.g. works councils or line managers, may support established or outsider groups, or play a crucial role in reducing power ratios within figurations. Moreover, the paper explores preconditions of a drag effect of habitus through the example of established-outsider figurations in internal marketisation at the organizational level. Social reciprocity between management and outsider groups may prove a vital precondition of habitual change in outsider groups, thereby adapting to new work-related demands. To conclude, potential future avenues of research are outlined

German works councils under pressure - institutional learning as a pathway to enhance their capacities of action

"This paper deals with institutional challenges German works councils face currently. These challenges consist of structural economic change from industrial to service sectors accompanied by an extension of 'co-determination-free-zones', an enhanced labour force diversity beyond the image of the male blue collar worker as the 'normal employee' works councils represent, the transformation of companies into network companies splitting up established works councils, co-management in times of competitive restructuring of firms and the emergence of new postfordistic production models with ambivalent impacts on working conditions. Moreover, works councils are challenged by a partial decentralisation of collective bargaining towards the establishment level dissolving the established division of labour between works councils and trade unions. These new challenges confront works councils with risks of structural overcharge endangering their institutional stability. Institutional learning may increase the institutional capabilities and competences required to works councils in order to meet new challenges. It could focus on a critical reflection of established practises in interest representation, utilising workforce diversity as a social resource of interest representation and promote co-operation between works councils in network companies or multinationals. However, works councils are not capable of meeting new challenges self-destined, rather they still depend on a supportive infrastructure of advice and consultancy provided by trade unions. In order to offer support tailored to the needs of works councils and to overcome their crisis in respect to social legitimacy trade unions will as well have to undergo processes of institutional learning to enhance their regional capacities of action, to promote innovative ideas or social issues and to utilise the increased workforce diversity as a starting point to attract new target groups of potential union members. The recognition of workforce diversity proves to be a significant prerequisite to draw on diversity as a social resource of institutional learning by works councils and unions." (author's remark

Indirect regulation - a remedy to cure the defects of European environmental policy? The EMAS-regulation

"The Eco-Management and Audit Scheme (EMAS) belongs to new forms of reflexive or indirect regulation in European environmental policy. The development of European environmental policy is outlined in respect to indirect regulation. By the example of EMAS the paper analyses the impacts of indirect regulation. At the first level the analysis focuses on the EMAS-participation within the European Union emphasising that EMAS turns out to be more a German rather than a European project. At the second level the analysis concentrates on the effects of EMAS-participation in respect to in-company processes of ecological modernisation as well as to external, mainly market-based impacts. The results are ambivalent: Positive effects are an improved level of in-company environmental protection and enhanced legal compliance. However, innovative potentials to organisational environmental learning are only partly exhausted. Market effects and improved relationships to external stakeholders seldom occur. To attribute these outcomes to specific instruments of environmental regulation would negate the multi-level and multi-centred institutional setting of European environmental policy. Therefore, starting points for a more effective European environmental policy are discussed, which combine aspects and instruments of direct and indirect regulation. Moreover, options to increase the participation of firms in EMAS are outlined." (author's abstract)Der Beitrag beschäftigt sich mit dem umweltpolitischen Instrument EMAS (Eco-Management-and-Audit-Scheme), einer neuen Form der reflexiven bzw. indirekten Regulierung in der europäischen Umweltpolitik. Die Untersuchung der Einflüsse der indirekten Regulierung gliedert sich dabei in die folgenden Kapitel: (1) die Modernisierung der europäischen Umweltpolitik durch die neue politische Vorgehensweise der indirekten Regulierung, (2) die politische und institutionelle Entwicklung der europäischen Umweltpolitik, (3) die politische Entstehung der EMAS-Regulierung und (4) deren Grundzüge, (5) der Umfang der EMAS-Partizipation in den EU-Mitgliedsstaaten sowie (6) die Einflüsse von EMAS bei Firmengründungen bzw. die internen und externen Effekte, am Beispiel Deutschlands. Gemäß der Untersuchung präsentiert sich EMAS als ein ambivalentes Instrument indirekter Regulierung hinsichtlich seiner internen und externen Einflüsse auf jene Firmen, die freiwillig an EMAS teilnehmen, als auch der Auswirkungen auf die EU-Umweltpolitik

Assessment of Various Density Functionals and Basis Sets for the Calculation of Molecular Anharmonic Force Fields

In a previous contribution (Mol. Phys. {\bf 103}, xxxx, 2005), we established the suitability of density functional theory (DFT) for the calculation of molecular anharmonic force fields. In the present work, we have assessed a wide variety of basis sets and exchange-correlation functionals for harmonic and fundamental frequencies, equilibrium and ground-state rotational constants, and thermodynamic functions beyond the RRHO (rigid rotor-harmonic oscillator) approximation. The fairly good performance of double-zeta plus polarization basis sets for frequencies results from an error compensation between basis set incompleteness and the intrinsic error of exchange-correlation functionals. Triple-zeta plus polarization basis sets are recommended, with an additional high-exponent $d$ function on second-row atoms. All conventional hybrid GGA functionals perform about equally well: high-exchange hybrid GGA and meta-GGA functionals designed for kinetics yield poor results, with the exception of of the very recently developed BMK functional which takes a middle position along with the HCTH/407 (second generation GGA) and TPSS (meta-GGA) functionals. MP2 performs similarly to these functionals but is inferior to hybrid GGAs such as B3LYP and B97-1.Comment: Int. J. Quantum Chem., in press (special issue on vibrational spectroscopies