Binding between endohedral Na atoms in Si clathrate I; a first principles study

We investigate the binding nature of the endohedral sodium atoms with the ensity functional theory methods, presuming that the clathrate I consists of a sheaf of one-dimensional connections of Na@Si$_{24}$ cages interleaved in three perpendicular directions. Each sodium atom loses 30% of the 3s$^1$ charge to the frame, forming an ionic bond with the cage atoms; the rest of the electron contributes to the covalent bond between the nearest Na atoms. The presumption is proved to be valid; the configuration of the two Na atoms in the nearest Si$_{24}$ cages is more stable by 0.189 eV than that in the Si$_{20}$ and Si$_{24}$ cages. The energy of the beads of the two distorted Na atoms is more stable by 0.104 eV than that of the two infinitely separated Na atoms. The covalent bond explains both the preferential occupancies in the Si$_{24}$ cages and the low anisotropic displacement parameters of the endohedral atoms in the Si$_{24}$ cages in the [100] directions of the clathrate I.Comment: First page: Affiliation added to PDF and PS versio

The economic design of a potential tradable permit system for SO2 emissions in the European Union

This paper contains two main parts. The first develops the issues of the European acid policy, and sets out the general background of the related regulatory regime. It also gives an overview of the theoretical and actual features of emissions trading mechanisms. It then considers the potential attractiveness of SO2 trading in the EU. This background throws light on the more specific analyses and proposals described in the second part of the paper, which is devoted to a presentation of possible frameworks for SO2 trading in the power generation sector in the EU. In section 2.1., we look at some key design variables. In section 2.2., we present three alternative ways of designing a trading scheme. In section 2.3., we consider specific issues related to zoning and scaling.

Accreditation for transnational research access to official micro-data in Europe

Accreditation is a central element of the framework for research access to micro-data that currently is understood to be a barrier for transnational access. To better understand the nature and causes of the problem, and to devise potential solutions, we have mapped current arrangements across European countries. We identify similarities and differences as well as areas for improvement. Our key results are encouraging: almost all European countries do provide research access to their micro-data, and most of them allow non-national European researchers to access their data, though under varying conditions. However, some obstacles remain, and some of them require negotiation and coordination at policy-making levels. To overcome existing barriers, we propose some potential options for the future and concrete steps towards improvement, which if explored from now on, could substantially improve access while still ensuring safe and lawful conditions, and reducing the administrative financial burden of data providers