The generality of the GUGA MRCI approach in COLUMBUS for treating complex quantum chemistry

The core part of the program system COLUMBUS allows highly efficient calculations using variational multireference (MR) methods in the framework of configuration interaction with single and double excitations (MR-CISD) and averaged quadratic coupled-cluster calculations (MR-AQCC), based on uncontracted sets of configurations and the graphical unitary group approach (GUGA). The availability of analytic MR-CISD and MR-AQCC energy gradients and analytic nonadiabatic couplings for MR-CISD enables exciting applications including, e.g., investigations of π-conjugated biradicaloid compounds, calculations of multitudes of excited states, development of diabatization procedures, and furnishing the electronic structure information for on-the-fly surface nonadiabatic dynamics. With fully variational uncontracted spin-orbit MRCI, COLUMBUS provides a unique possibility of performing high-level calculations on compounds containing heavy atoms up to lanthanides and actinides. Crucial for carrying out all of these calculations effectively is the availability of an efficient parallel code for the CI step. Configuration spaces of several billion in size now can be treated quite routinely on standard parallel computer clusters. Emerging developments in COLUMBUS, including the all configuration mean energy multiconfiguration self-consistent field method and the graphically contracted function method, promise to allow practically unlimited configuration space dimensions. Spin density based on the GUGA approach, analytic spin-orbit energy gradients, possibilities for local electron correlation MR calculations, development of general interfaces for nonadiabatic dynamics, and MRCI linear vibronic coupling models conclude this overview

La naissance du christianisme et de la « Grande Eglise »

Le christianisme antique est un phénomène bien attesté même si de fortes inégalités documentaires peuvent être observées en matière de types de témoignages, de chronologie ou de géographie.&nbsp;</p

SPECIATION OF THE PLUTONYL FORMS OF PLUTONIUM

(Present Address: ASC/MSRC 2435 5th St. B676, Wright-Patterson AFB, Ohio, 45433)Author Institution: Department of Chemistry, The Ohio State UniversityPlutonium ions in the 5+ and 6+ oxidation states are found in the plutonyl forms, $(PuO_{2})^{+}$ and $(PuO_{2})^{2+}$, respectively. The speciation of these two complexes was examined using density functional theory (DFT) methods. More specifically, we use the Amsterdam Density functional (ADF) code, which includes relativistic effects and generalized gradient corrections. The coordination number for the number of water molecules around each of these species, as well as the bond length between the plutonium ion and the water-based oxygen atoms, are determined and compared to experiment - which uses XANES (X-ray Absorption Near-Edge Spectroscopy) and eXAFS (extended X-ray Absorption Fine Structure) spectroscopy. Furthermore, we have examined different geometrical arrangements for the water molecules in these complexes. Optimized structures with real frequencies are obtained and provide us insight into the chemical interactions involved in the solvation of plutonium species

STUDIES ON PLUTONIUM SPECIES

$^{a}$Present Address: Ohio Supercomputer Center, ASC/MSRC 2435 $5^{th}$ St. B676, Wright-Patterson AFB, Ohio, 45433Author Institution: The Ohio State University; Department of Chemistry, The Ohio State UniversityWe will report the status of our ongoing calculations on species containing plutonium. These have had a two-pronged approach: Density Functional Theory Methods (using ADF) studying the speciation of the various plutonium ions in water and multi-reference spin-orbit configuration interaction calculations (using COLUMBUS) studying the electronic structure of plutonyl ions. The speciation studies have concentrated on the comparison of coordination number and Pu-O bond lengths to experimental (from XANES and eXAFS) results. Recently, the electronic structure methods have allowed us to calculate transition spectra. The results for $PuO_{2}^{2+}$ will be reported and compared to experiment

THE ELECTRONIC STRUCTURE OF THE PLUTONYLION

Author Institution: Department of Chemistry, The Ohio State UniversityRestricted Hartree-Fock (RHF) and spin-orbit configuration-interaction (SOCI) calculations were performed on the ground and low-lying excited states of the plutonyl ion, $PuO_{2}^{2+}$. These results are compared to density functional theory (DFT) results obtained using generalized gradient corrections. The low energy transitions are $f \to f$. Information on the vibrational modes will also be presented. For the ab initio work, the actinides are modeled with relativistic effective core potentials and Gaussian correlation consistent double-zeta plus polarization basis sets. The DFT work used Slater basis sets

SPECIATION OF PLUTONIUM IN WATER

Author Institution: Department of Chemistry, The Ohio State University; Chemical Technology Division/Materials Science Division, Argonne National Laboratory; Department of Chemistry, The Ohio State UniversityThe speciation of plutonium in water was modeled using both ab initio quantum chemistry and density functional theory (DFT) methods. Aqueous plutonium exists in four oxidation states: $+3, +4, +5$, and $+6$. The first two forms exist as the bare ions, but the $+5$ and $+6$ states exist as $(PuO_{2})^{+}$ and $(PuO_{2})^{2+}$ species, respectively. The coordination number for the number of water molecules around each of these species is determined and compared to experiment - which uses XANES (X-ray Absorption Near-Edge Spectroscpy) and eXAFS (extended X-ray Absorption Fine Structure) spectroscopy. The DFT calculations include generalized gradient corrections and the quantum chemistry calculations are at the spin-orbit configuration interaction level

SPECIATION OF NEPTUNIUM IN WATER

Author Institution: Department of Chemistry, The Ohio State University; Department of Chemistry, Ohio Wesleyan University; Department of Chemistry, The Ohio State UniversityThe speciation of neptunium in water was modeled using density functional theory (DFT) methods. Aqueous neptunium exists in four oxidation states: $+3, +4, +5$, and $+6$. The first two forms exist as the bare ions, but the $+5$ and $+6$ states exist as $(NpO_{2})^{+}$ and $(NpO_{2})^{2+}$ species, respectively. The coordination number for the number of water molecules around each of these species is determined and compared to experiment - which uses XANES (X-ray Absorption Near-Edge Spectroscopy) and eXAFS (extended X-ray Absorption Fine Structure) spectroscopy. The DFT calculations include generalized gradient corrections

TOPOLOGY AND BASICITY IN POLYOXOVANADATES: AB INTITIO STUDY OF THE CAGED MOLECULES [V18O42]12[V_{18}O_{42}]^{12} AND [V7O12(O3PH)6][V_{7} O_{12}(O_{3}PH)_{6}]

Author Institution: Laboratoire de Chimie Quantique, UPR 139 du CNRS Universit\'e Louis Pasteur; Laboratoire de Cristallographie et Mod\'{e}lisation des Mat\'{e}raux Min\'{e}raux et Biologigues, CCM^{3}B, URA 809 du CNRS, University Henri Poincar\'e-NancyAb initio Hartree-Fock calculations have been carried out on the octadecavanadate ion $[V_{18}O_{42}]^{12-}(1)$, On its protonated derivative $[H_{4}V_{18}O_{42}]^{8-}(2)$, and on the vanadophosphate cluster $[V_{7}O_{12}(O_{3}PH)_{6}]^{-}(3)$, taken as a model for $[V_{7}O_{12}(O_{3}PR)_{6}]^{-} (3^{\prime})$. The spheroidal clusters (2) and $(3^{\prime})$ have been recently characterized as ``electronically inverse hosts” in the encapsulation complexes $Cs_{9}[X@H_{4}V_{18}O_{42}]\cdot 12H_{2}O (X = Br, I)$ and $(PH_{4}P)_{2}[Cl@V_{7}O_{12}(O_{3}PPh)_{6}]$. An estimate of the electrostatic potential distribution including the contribution of the lattice potential yields highly positive values of the potential inside the host cavities for (2) and (3). Those values are larger than the electrostatic potential computed at a vacant chloride site of the CsCl crystal, thus explaining the thermodynamic stability of the encapsulated anions