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Different structures of gallium have been studied by means of densityfunctional theory. The density of states of orthorhombic Ga, the only elemental solid exhibiting both metallic and molecular characters at zero pressure, shows a pseudogap at the Fermi energy. Complex analysis of the relation between lattice structure and the corresponding electronic properties allows us to throw light upon an origin of the pseudogap. We have found that the freeelectronlike behavior which is a property of the highpressure bct and fcc phases of gallium depends strongly on the arrangement of atoms in the buckled planes, one of the building blocks of the orthorhombic gallium.
Coupledcluster pair energies calculated for localized orbitals in finite lithium clusters are used for an estimate of the cohesive energy and the lattice constant of the bcc lithium crystal. It is shown that the results converge reasonably fast with cluster size and are of comparable quality with conventional density functional ones for the infinite solid.
The method of increments is applied to the adsorption energy of H_{2} S on a graphene layer using a CCSD(T) correlation treatment. We determine the incremental expansion for the correlation contribution to the adsorption energy in terms of localized orbitals of the molecule and the surface. The changes in the correlation energy of the molecule and the individual localized surface orbitals are repulsive and small, the major contributions arise from the joint correlation of molecule and surface orbitals.
C_{6}F_{6}^{.+}, Os_{2}F_{11}^{} and C_{6}F_{6}^{.+} Sb_{2}F_{11}^{} have isomorphous crystal structures and each contain two different C_{6}F_{6}^{.+} cations. One is a quinoid structure, the other bisallyl structure. Calculations show that indeed two such JahnTeller distorted structures coexist with essentially the same energy. This seems to be a case of bondstretch isomerism.
Applying the method of increments, we have performed MP2 and CCSD(T) calculations for the physisorption of CO on a cerium site on the ceria(111) surface. Our calculations predict an interaction energy of 0.28 eV. We have compared our calculations to previous CCSD(T) calculations for the physisorption of CO on a cerium site on the ceria(110) surface and found a difference in the interaction energy that is related to the different structure of the two surfaces. On the ceria(110) surface only 30% of the interaction energy originate from electron correlation effects, but on the ceria(111) surface almost the entire binding energy (80%) is due to electron correlation effects. Analyses of the interaction energy contributions show that most of the electron correlation part originates from the interaction of CO with the O ions in the topmost surface layer.
Ab initio electron correlation calculations based on quantumchemical methods are successfully applied to a metallic system. To deal with the two distinct problems that occur in metals, the difficulty of localization of the orbitals and the generation of clusters with neutral atoms in the center, we suggest an embedding scheme which has itself no metallic character but can mimic the metal in the internal region, where the atoms are correlated. The long range non additive contributions of metalicity and correlation are treated with the method of increments. The approach has been tested on the group 2 and 12 metals (Be, Mg, Zn, Cd, and Hg). The obtained groundstate properties are shown to agree well with the experimental values. Moreover, taking into account the advantage of the method of increments to analyse the individual contributions to correlation energy it is possible to clarify some aspects of the structural features of the group12 metals.
We have investigated the electron correlation contribution to the interaction energy of the N_{2}O/ceria(111) system at the CCSD(T) level. N_{2}O binds either with the Nend towards the surface with an interaction energy E_{int.}= 0.23 eV or with the Oend with E_{int.}= 0.27 eV. In the former case almost the entire binding energy is due to electron correlation effects, in the latter these effects contribute with about 60%. Analyses of the interaction energy contributions show that most of the electron correlation part originates from the interaction of N_{2}O with the O ions in the topmost surface layer.
The purpose of this paper is to present tests that are suitable to perform as an assessment of the quality of embeddedcluster models for ionic surfaces. Bulk and surface clusters of CeO_{2} were constructed and the embedding quality was evaluated as a function of cluster size and stoichiometry. Out of the properties evaluated, it is found that the difference electron density (between the embedded cluster model and an equivalent periodic slab model), as well as the electrostatic potential above the surface are very sensitive to the embedding quality and can successfully be used as selection tools in the quality assessment. This was confirmed by subsequent CO_{2} physisorption calculations for a number of embedded CeO_{2}(111) clusters.
For a laser driven molecule, we show that the ionization and the dissociation channels can be separated by preparing the molecule in a speciﬁc vibrational state. Speciﬁcally, we investigate the dynamics of the hydrogen molecular ion under a femtosecond infrared laser ﬁeld aligned with the molecular axis. We ﬁnd dissociation probabilities of more than 60 %, considerably higher than reported so far. We demonstrate that a full dimensional description of the electron dynamics is necessary to obtain accurate results for the combined ionization/dissociation dynamics.
Common myth suggests synchronicity and unidirectionality of nuclear and electronic ﬂuxes. Accurate quantum dynamics simulations of the vibrating model system, aligned Hþ2 , conﬁrm this rule, but with exceptional opposite behaviours during short periods in the attosecond time domain. The ratio of electronic versus nuclear ﬂuxes increases systematically, from small to large amplitude nuclear motions. Visualization of the electronic and nuclear densities and ﬂux densities reveals that this is due to broader dispersion of electronic wavepackets compared to nuclear ones. The accurate results validate an efficient general method for quantum calculations of the ﬂuxes in terms of densities, not ﬂux densities. 
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This page was last modified on December 07, 2010, at 02:11 PM 