Sökning: "density matrix"

Visar resultat 1 - 5 av 328 avhandlingar innehållade orden density matrix.

  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. Strongly Correlated Models in One Dimension from a Density Matrix Renormalization Group Perspective

    Författare :Stefan Rommer; Chalmers tekniska högskola; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; matrix product states; impurities; density matrix renormalization group; Heisenberg model; spin chain; DMRG;

    Sammanfattning : The density matrix renormalization group (DMRG) is a numerical method for studying low dimensional strongly correlated models. The study of these models is one of the most active areas of condensed matter physics today and has been spurred not only by the discovery of high temperature superconductivity but also by experiments on new compounds. LÄS MER

  4. 3. Sparse Matrices in Self-Consistent Field Methods

    Författare :Emanuel Rubensson; Pawel Salek; Hans Ågren; Anders Niklasson; Axel Ruhe; KTH; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; sparse matrix; self-consistent field; Hartree-Fock; Density Functional Theory; Density Matrix Purification; Theoretical chemistry; Teoretisk kemi;

    Sammanfattning : This thesis is part of an effort to enable large-scale Hartree-Fock/Kohn-Sham (HF/KS) calculations. The objective is to model molecules and materials containing thousands of atoms at the quantum mechanical level. HF/KS calculations are usually performed with the Self-Consistent Field (SCF) method. LÄS MER

  5. 4. The density-matrix formalism for description of step-wise laser-excitations of atoms and molecules in high-collisional media

    Författare :Peter Ljungberg; Chalmers tekniska högskola; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; density-matrix; pulsed lasers; anomalous saturation curved; laser spectroscopy; stark split; degenerate states; rate-equations;

    Sammanfattning : .... 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