Causes of high-temperature superconductivity in the hydrogen sulfide electron-phonon system

The electron and phonon spectra, as well as the density of electron and phonon states of the stable orthorhombic structure of hydrogen sulfide (SH2) at pressures 100-180 GPa have been calculated. It is found that the set of parallel planes of hydrogen atoms is formed at pressure ~175 GPa as a result of structural changes in the unit cell of the crystal under pressure. There should be complete concentration of hydrogen atoms in these planes. As a result the electron properties of the system acquire a quasi-two-dimensional character. The features of in phase and antiphase oscillations of hydrogen atoms in these planes leading to two narrow high-energy peaks in the phonon density of states are investigated

Electro and gamma nuclear physics in Geant4

Adequate description of electro and gamma nuclear physics is of utmost importance in studies of electron beam-dumps and intense electron beam accelerators. I also is mandatory to describe neutron backgrounds and activation in linear colliders. This physics was elaborated in Geant4 over the last year, and now entered into the stage of practical application. In the {\sc Geant4} Photo-nuclear data base there are at present about 50 nuclei for which the Photo-nuclear absorption cross sections have been measured. Of these, data on 14 nuclei are used to parametrize the gamma nuclear reaction cross-section The resulting cross section is a complex, factorized function of $A$ and $e = log(E_\gamma)$, where $E_\gamma$ is the energy of the incident photon. Electro-nuclear reactions are so closely connected with Photo-nuclear reactions that sometimes they are often called ``Photo-nuclear''. The one-photon exchange mechanism dominates in Electro-nuclear reactions, and the electron can be substituted by a flux of photons. Folding this flux with the gamma-nuclear cross-section, we arrive at an acceptable description of the electro-nuclear physics. Final states in gamma and electro nuclear physics are described using chiral invariant phase-space decay at low gamma or equivalent photon energies, and quark gluon string model at high energies. We will present the modeling of this physics in {\sc Geant4}, and show results from practical applications.Comment: Computing in High Energy and Nuclear Physics, La Jolla, California, March 24-28, 2003 1 tar fil

COMe: the ontology of bioinorganic proteins

BACKGROUND: Many characterised proteins contain metal ions, small organic molecules or modified residues. In contrast, the huge amount of data generated by genome projects consists exclusively of sequences with almost no annotation. One of the goals of the structural genomics initiative is to provide representative three-dimensional (3-D) structures for as many protein/domain folds as possible to allow successful homology modelling. However, important functional features such as metal co-ordination or a type of prosthetic group are not always conserved in homologous proteins. So far, the problem of correct annotation of bioinorganic proteins has been largely ignored by the bioinformatics community and information on bioinorganic centres obtained by methods other than crystallography or NMR is only available in literature databases. RESULTS: COMe (Co-Ordination of Metals) represents the ontology for bioinorganic and other small molecule centres in complex proteins. COMe consists of three types of entities: 'bioinorganic motif' (BIM), 'molecule' (MOL), and 'complex proteins' (PRX), with each entity being assigned a unique identifier. A BIM consists of at least one centre (metal atom, inorganic cluster, organic molecule) and two or more endogenous and/or exogenous ligands. BIMs are represented as one-dimensional (1-D) strings and 2-D diagrams. A MOL entity represents a 'small molecule' which, when in complex with one or more polypeptides, forms a functional protein. The PRX entities refer to the functional proteins as well as to separate protein domains and subunits. The complex proteins in COMe are subdivided into three categories: (i) metalloproteins, (ii) organic prosthetic group proteins and (iii) modified amino acid proteins. The data are currently stored in both XML format and a relational database and are available at . CONCLUSION: COMe provides the classification of proteins according to their 'bioinorganic' features and thus is orthogonal to other classification schemes, such as those based on sequence similarity, 3-D fold, enzyme activity, or biological process. The hierarchical organisation of the controlled vocabulary allows both for annotation and querying at different levels of granularity

First-principles studies of the structure and dynamics of biomolecules

First-principles biosimulations have become an essential tool in the study of atoms and molecules and, increasingly, in modelling complex systems as those arising in biology. With the appearance of density-functional theory, and gradient-corrected exchange-correlation functionals, the ability to obtain an accurate enough solutions to the electronic Schrödinger equation for systems containing hundreds (or even thousands) of atoms has revolutionized biophysics and biochemistry. Biological systems exhibit a far higher degree of complexity than those studied in many other fields of physics. The sizes of the systems, long time scale of processes, the effect of the environment, and the range of intermolecular interactions provide challenging problems for the application of first-principles quantum mechanical simulations to biomolecular studies. This thesis concentrates on first-principles electronic structure calculations of various biological systems and processes. The dynamics of the active center of myoglobin has been studied by means of Born-Oppenheimer molecular dynamics. Similar methodology has been used to investigate the effect of hydration of the L-alanine amino acid and to predict its actual structure in aqueous solution at finite temperature. The effect of the environment, and the actual structure of several biomolecules in water have been investigated by means of vibrational spectra calculations. Different continuum models have been employed in calculations of the vibrational absorption, vibrational dichroism, Raman and Raman optical activity spectra. The treatment of large, biological systems, such as proteins in aqueous solution, entirely by ab initio methods is extremely expensive. The thesis demonstrates various approaches to overcome size and time scale limits. The work presented here is an example of how quantum mechanical techniques can successfully be applied to biologically relevant problems in rather large and complex systems.reviewe