Change search
Refine search result
1 - 7 of 7
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Armiento, Rickard
    KTH, School of Engineering Sciences (SCI), Physics.
    Numerical Integration of functions originating from quantum mechanicsReport (Other academic)
    Abstract [en]

    Applications in quantum physics commonly involve large batches of integrals of smooth but veryoscillatory functions. The purpose of this work is to benchmark and compare different numerical algorithms for evaluating such integrals. The routines studied include: two from the QUADPACK package based on Gauss-Kronrod quadrature; one routine based on Patterson’s improvements of Gauss-Kronrod quadrature; and two routines that use a non-standard algorithm of applying quadrature-like rules of unrestricted order. The last algorithm has been seen in previous works,but is not in wide-spread use. The present work includes optimized implementations of this algorithm for both serial and parallel computation.

  • 2.
    Armiento, Rickard
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    The many-electron energy in density functional theory: from exchange-correlation functional design to applied electronic structure calculations2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The prediction of properties of materials and chemical systems is a key component in theoretical and technical advances throughout physics, chemistry, and biology. The properties of a matter system are closely related to the configuration of its electrons. Computer programs based on density functional theory (DFT) can calculate the configuration of the electrons very accurately. In DFT all the electronic energy present in quantum mechanics is handled exactly, except for one minor part, the exchange-correlation (XC) energy. The thesis discusses existing approximations of the XC energy and presents a new method for designing XC functionals---the subsystem functional scheme. Numerous theoretical results related to functional development in general are presented. An XC functional is created entirely without the use of empirical data (i.e., from so called first-principles). The functional has been applied to calculations of lattice constants, bulk moduli, and vacancy formation energies of aluminum, platinum, and silicon. The work is expected to be generally applicable within the field of computational density functional theory.

  • 3.
    Armiento, Rickard
    et al.
    KTH, Superseded Departments, Physics.
    Matsson, A. E.
    Interface Sci. Department MS 1415, Sandia National Laboratories, Albuquerque.
    Subsystem functionals: investigating the exchange energy per particle2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 16, p. 1651171-16511717Article in journal (Refereed)
    Abstract [en]

    A viable way of extending the successful use of density-functional theory into studies of even more complex systems than are addressed today has been suggested by Kohn and Mattsson [W. Kohn and A. E. Mattsson, Phys. Rev. Lett. 81, 3487 (1998); A. E. Mattsson and W. Kohn, J. Chem. Phys. 115, 3441 (2001)], and is further developed in this work. The scheme consists of dividing a system into subsystems and applying different approximations for the unknown (but general) exchange-correlation energy functional to the different subsystems. We discuss a basic requirement on approximative functionals used in this scheme; they must all adhere to a single explicit choice of the exchange-correlation energy per particle. From a numerical study of a model system with a cosine effective potential, the Mathieu gas, and one of its limiting cases, the harmonic oscillator model, we show that the conventional definition of the exchange energy per particle cannot be described by an analytical series expansion in the limit of slowly varying densities. This indicates that the conventional definition is not suitable in the context of subsystem functionals. We suggest alternative definitions and approaches to subsystem functionals for slowly varying densities and discuss the implications of our findings on the future of functional development.

  • 4.
    Armiento, Rickard
    et al.
    KTH, Superseded Departments, Physics.
    Mattsson, A. E.
    Compl. Mat. and Molecular Biology, Sandia National Laboratories, Albuquerque.
    Alternative separation of exchange and correlation in density-functional theory2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, no 24, p. 2451201-2451205Article in journal (Refereed)
    Abstract [en]

    It has recently been shown that local values of the conventional exchange energy per particle cannot be described by an analytic expansion in the density variation. Yet, it is known that the total exchange-correlation (XC) energy per particle does not show any corresponding nonanalyticity. Indeed, the nonanalyticity is here shown to be an effect of the separation into conventional exchange and correlation. We construct an alternative separation in which the exchange part is made well behaved by screening its long-ranged contributions, and the correlation part is adjusted accordingly. This alternative separation is as valid as the conventional one, and introduces no new approximations to the total XC energy. We demonstrate functional development based on this approach by creating and deploying a local-density-approximation-type XC functional. Hence, this work includes both the theory and the practical calculations needed to provide a starting point for an alternative approach towards improved approximations of the total XC energy.

  • 5.
    Armiento, Rickard
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Mattsson, A. E.
    Computational Materials and Molecular Biology MS 1110, Sandia National Laboratories, Albuquerque.
    Functional designed to include surface effects in self-consistent density functional theory2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 8, p. 085108-Article in journal (Refereed)
    Abstract [en]

    We design a density-functional-theory (DFT) exchange-correlation functional that enables an accurate treatment of systems with electronic surfaces. Surface-specific approximations for both exchange and correlation energies are developed. A subsystem functional approach is then used: an interpolation index combines the surface functional with a functional for interior regions. When the local density approximation is used in the interior, the result is a straightforward functional for use in self-consistent DFT. The functional is validated for two metals (Al, Pt) and one semiconductor (Si) by calculations of (i) established bulk properties (lattice constants and bulk moduli) and (ii) a property where surface effects exist (the vacancy formation energy). Good and coherent results indicate that this functional may serve well as a universal first choice for solid-state systems and that yet improved functionals can be constructed by this approach.

  • 6.
    Mattsson, A. E.
    et al.
    Multiscale Computational Materials Methods, MS 1110, Sandia National Laboratories, Albuquerque.
    Armiento, Rickard
    KTH, School of Engineering Sciences (SCI), Physics.
    Schultz, P. A.
    Multiscale Computational Materials Methods, MS 1110, Sandia National Laboratories, Albuquerque.
    Mattsson, T. R.
    HEDP Theory/ICF Target Design, MS 1186, Sandia National Laboratories, Albuquerque.
    Nonequivalence of the generalized gradient approximations PBE and PW912006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 19, p. 195123-Article in journal (Refereed)
    Abstract [en]

    Two of the most popular generalized gradient approximations used in the applications of the density functional theory, PW91 and PBE, are generally regarded as essentially equivalent. They produce similar numerical results for many simple properties, such as lattice constants, bulk moduli, and atomization energies. We examine more complex properties of systems with electronic surface regions, with the specific application of the monovacancy formation energies of Pt and Al. A surprisingly large and consistent discrepancy between PBE and PW91 results is obtained. This shows that despite similarities found between some simple material properties, PBE and PW91 are not equivalent. The differences obtained for the monovacancy formation energies are related to differences in surface intrinsic errors which are substantiated using the idealized, well-controlled, jellium surface model. In view of the differences obtained with the PW91 and PBE functionals we develop separate surface intrinsic error corrections for these and revisit some earlier results.

  • 7.
    Perdew, John P.
    et al.
    Department of Physics and Quantum Theory Group, Tulane University, New Orleans,.
    Tao, Jianmin
    Department of Physics and Quantum Theory Group, Tulane University, New Orleans,.
    Armiento, Rickard
    KTH, Superseded Departments, Physics.
    How to tell an atom from an electron gas: a semi-local index of density inhomogeneity2003In: Acta physica et chimica debrecina, Vol. 36, no 25Article in journal (Refereed)
    Abstract [en]

    From a global perspective, the density of an atom is strongly inhomogeneous and not at all like the density of a uniform or nearly-uniform electron gas. But, from the semi-local or myopic perspective of standard density functional approximations to the exchange-correlation energy, it is not so easy to tell an atom from an electron gas. We address the following problem:  Given the ground-state electron density n and orbital kinetic energy density in the neighborhood of a point r, can we construct an inhomogeneity index which approaches zero for weakly-inhomogeneous densities and unity for strongly-inhomogeneous ones? The solution requires not only the usual local ingredients of a meta-generalized gradient approximation, but also r and r2. The inhomogeneity index is displayed for atoms, and for model densities of metal surfaces and bulk metals. Scaling behavior and a possible application to functional interpolation are discussed.

    

1 - 7 of 7
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf