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Visar resultat 1 - 5 av 10 avhandlingar som matchar ovanstående sökkriterier.

1. 1. Matrix Algebra for Quantum Chemistry

   Författare :Emanuel H. Rubensson; Pawel Salek; Stefan Goedecker; KTH; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; linear scaling; reduced complexity; electronic structure; density functional theory; Hartree-Fock; density matrix purification; congruence transformation; inverse factorization; eigenvalues; eigenvectors; numerical linear algebra; occupied subspace; canonical angles; invariant subspace; Theoretical chemistry; Teoretisk kemi;

   Sammanfattning : This thesis concerns methods of reduced complexity for electronic structure calculations.  When quantum chemistry methods are applied to large systems, it is important to optimally use computer resources and only store data and perform operations that contribute to the overall accuracy. LÄS MER

3. 2. Parallelization of dynamic algorithms for electronic structure calculations

   Författare :Anton G. Artemov; Emanuel H. Rubensson; Maya Neytcheva; Bo Kågström; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; parallelization; task-based programming; matrix algorithms; sparse matrices; inverse factorization; localized computations; density matrix methods; electronic structure calculations; Scientific Computing; Beräkningsvetenskap;

   Sammanfattning : The aim of electronic structure calculations is to simulate behavior of complex materials by resolving interactions between electrons and nuclei in atoms at the level of quantum mechanics. Progress in the field allows to reduce the computational complexity of the solution methods to linear so that the computational time scales proportionally to the size of the physical system. LÄS MER

4. 3. Sources of dioxins and other POPs to the marine environment : Identification and apportionment using pattern analysis and receptor modeling

   Författare :Kristina Sundqvist; Karin Wiberg; Mats Tysklind; Paul Geladi; Miriam Diamond; Umeå universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; air-water gas exchange; chiral; congener pattern; enantiomer; enantiomeric fraction; fugacity; HCH; hexachlorocyclohexane; homologue profile; indicator congener; isomer pattern; pattern analysis; PCA; PCB; PCDD F; PMF; polychlorinated dibenzofuran; polychlorinated dibenzo-p-dioxin; polychlorinated biphenyl; positive matrix factorization; principal component analysis; receptor modeling; source apportioning; source; source tracing; Environmental chemistry; Miljökemi; Persistent organic compounds; Persistenta organiska föreningar;

   Sammanfattning : In the studies underlying this thesis, various source tracing techniques were applied to environmental samples from the Baltic region. Comprehensive sampling and analysis of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in surface sediments in Swedish coastal and offshore areas resulted in a unique data set for this region. LÄS MER

5. 4. Impact of residential wood combustion on urban air quality

   Författare :Patricia Krecl; Christer Johansson; Johan Ström; Tami Bond; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; residential wood combustion; air quality; aerosols; black carbon; polycyclic aromatic hydrocarbons; particulate matter; particle size distributions; source apportionment; positive matrix factorization; compound-specific radiocarbon analysis; Earth sciences; Geovetenskap; Applied Environmental Science; tillämpad miljövetenskap;

   Sammanfattning : Wood combustion is mainly used in cold regions as a primary or supplemental space heating source in residential areas. In several industrialized countries, there is a renewed interest in residential wood combustion (RWC) as an alternative to fossil fuel and nuclear power consumption. LÄS MER

7. 5. Efficient Density Matrix Methods for Large Scale Electronic Structure Calculations

   Författare :Anastasia Kruchinina; Emanuel H. Rubensson; Elias Rudberg; David Bowler; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; electronic structure; linear scaling; density matrix; density functional theory; Hartree-Fock; recursive polynomial expansion; density matrix purification; eigenvectors; molecular orbitals; stopping criteria; inverse factorization; matrix sparsity; parallelization; Scientific Computing; Beräkningsvetenskap;

   Sammanfattning : Efficient and accurate methods for computing the density matrix are necessary to be able to perform large scale electronic structure calculations. For sufficiently sparse matrices, the computational cost of recursive polynomial expansions to construct the density matrix scales linearly with increasing system size. LÄS MER