1,508 research outputs found
Beyond density functional theory: the domestication of nonlocal potentials
Due to efficient scaling with electron number N, density functional theory
(DFT) is widely used for studies of large molecules and solids. Restriction of
an exact mean-field theory to local potential functions has recently been
questioned. This review summarizes motivation for extending current DFT to
include nonlocal one-electron potentials, and proposes methodology for
implementation of the theory. The theoretical model, orbital functional theory
(OFT), is shown to be exact in principle for the general N-electron problem. In
practice it must depend on a parametrized correlation energy functional.
Functionals are proposed suitable for short-range Coulomb-cusp correlation and
for long-range polarization response correlation. A linearized variational
cellular method (LVCM) is proposed as a common formalism for molecules and
solids. Implementation of nonlocal potentials is reduced to independent
calculations for each inequivalent atomic cell.Comment: Accepted for publication in Modern Physics Letters B (2004
The Application of Project Management Standards and Success Factors to the Development of a Project Management Assessment Tool
AbstractIn spite of all that is known about project management best practices, they are often absent from typical construction projects. This has motivated our interest in developing a tool to assess construction project management practices, focusing on the assessment of individual project practices. We will also explore project outcomes and their correlation with project management practices-potentially identifying project management value. Previous efforts have addressed project management assessment. The paper describes examples that assess an individual's project management skills and approaches that examine the project management competencies of organizations. In contrast to these, our focus is on assessing the project management practices that have been implemented for specific construction projects. A central component of any assessment scheme is the identification of specific elements to be assessed (the assessment “targets”). We intend to draw heavily upon established project management standards and project success factors from previous research to provide the specific targets and benchmarks to be assessed. These include the Project Management Body of Knowledge (PMBOK) by the PM Institute, the IPMA Competence Baseline (ICB) by the International PM Association, ISO 9000, and Prince2 by The Office of Government Commerce UK. This paper describes how these standards are integrated into the project management assessment tool. It discusses the theoretical foundations for the project management assessment tool and the methodologies used for developing the tool and for applying the tool to specific project situations
Transient rectification of Brownian diffusion with asymmetric initial distribution
In an ensemble of non-interacting Brownian particles, a finite systematic
average velocity may temporarily develop, even if it is zero initially. The
effect originates from a small nonlinear correction to the dissipative force,
causing the equation for the first moment of velocity to couple to moments of
higher order. The effect may be relevant when a complex system dissociates in a
viscous medium with conservation of momentum
Multiconfiguration electron density function for the ATSP2K-package
A new ATSP2K module is presented for evaluating the electron density function
of any multiconfiguration Hartree-Fock or configuration interaction wave
function in the non relativistic or relativistic Breit-Pauli approximation. It
is first stressed that the density function is not a priori spherically
symmetric in the general open shell case. Ways of building it as a spherical
symmetric function are discussed, from which the radial electron density
function emerges. This function is written in second quantized coupled
tensorial form for exploring the atomic spherical symmetry. The calculation of
its expectation value is performed using the angular momentum theory in
orbital, spin, and quasispin spaces, adopting a generalized graphical
technique. The natural orbitals are evaluated from the diagonalization of the
density matrix
Exploring Biorthonormal Transformations of Pair-Correlation Functions in Atomic Structure Variational Calculations
Multiconfiguration expansions frequently target valence correlation and
correlation between valence electrons and the outermost core electrons.
Correlation within the core is often neglected. A large orbital basis is needed
to saturate both the valence and core-valence correlation effects. This in turn
leads to huge numbers of CSFs, many of which are unimportant. To avoid the
problems inherent to the use of a single common orthonormal orbital basis for
all correlation effects in the MCHF method, we propose to optimize independent
MCHF pair-correlation functions (PCFs), bringing their own orthonormal
one-electron basis. Each PCF is generated by allowing single- and double-
excitations from a multireference (MR) function. This computational scheme has
the advantage of using targeted and optimally localized orbital sets for each
PCF. These pair-correlation functions are coupled together and with each
component of the MR space through a low dimension generalized eigenvalue
problem. Nonorthogonal orbital sets being involved, the interaction and overlap
matrices are built using biorthonormal transformation of the coupled basis sets
followed by a counter-transformation of the PCF expansions.
Applied to the ground state of beryllium, the new method gives total energies
that are lower than the ones from traditional CAS-MCHF calculations using large
orbital active sets. It is fair to say that we now have the possibility to
account for, in a balanced way, correlation deep down in the atomic core in
variational calculations
On the Reduction in Accuracy of Finite Difference Schemes on Manifolds without Boundary
We investigate error bounds for numerical solutions of divergence structure
linear elliptic PDEs on compact manifolds without boundary. Our focus is on a
class of monotone finite difference approximations, which provide a strong form
of stability that guarantees the existence of a bounded solution. In many
settings including the Dirichlet problem, it is easy to show that the resulting
solution error is proportional to the formal consistency error of the scheme.
We make the surprising observation that this need not be true for PDEs posed on
compact manifolds without boundary. By carefully constructing barrier
functions, we prove that the solution error achieved by a scheme with
consistency error is bounded by
in dimension . We also provide a specific
example where this predicted convergence rate is observed numerically. Using
these error bounds, we further design a family of provably convergent
approximations to the solution gradient.Comment: 28 pages, 7 figure
Efficient Algorithm for Asymptotics-Based Configuration-Interaction Methods and Electronic Structure of Transition Metal Atoms
Asymptotics-based configuration-interaction (CI) methods [G. Friesecke and B.
D. Goddard, Multiscale Model. Simul. 7, 1876 (2009)] are a class of CI methods
for atoms which reproduce, at fixed finite subspace dimension, the exact
Schr\"odinger eigenstates in the limit of fixed electron number and large
nuclear charge. Here we develop, implement, and apply to 3d transition metal
atoms an efficient and accurate algorithm for asymptotics-based CI.
Efficiency gains come from exact (symbolic) decomposition of the CI space
into irreducible symmetry subspaces at essentially linear computational cost in
the number of radial subshells with fixed angular momentum, use of reduced
density matrices in order to avoid having to store wavefunctions, and use of
Slater-type orbitals (STO's). The required Coulomb integrals for STO's are
evaluated in closed form, with the help of Hankel matrices, Fourier analysis,
and residue calculus.
Applications to 3d transition metal atoms are in good agreement with
experimental data. In particular we reproduce the anomalous magnetic moment and
orbital filling of Chromium in the otherwise regular series Ca, Sc, Ti, V, Cr.Comment: 14 pages, 1 figur
MAPPER, a low-level geographic information system
A Low-Level Geographic Information System (LL-GIS) was developed to provide a simple low-cost mapping program which can be executed in any personal computer, by individuals with different levels of knowledge in computing. MAPPER is an add-on module of FishBase - a global database with key information on the biology of fish - where it creates on-screen maps with information on biodiversity and the occurrence of species. In another application, MAPPER is used to display and analyzed geographical information on the Philippines
Implementation of screened hybrid functionals based on the Yukawa potential within the LAPW basis set
The implementation of screened hybrid functionals into the WIEN2k code, which
is based on the LAPW basis set, is reported. The Hartree-Fock exchange energy
and potential are screened by means of the Yukawa potential as proposed by
Bylander and Kleinman [Phys. Rev. B 41, 7868 (1990)] for the calculation of the
electronic structure of solids with the screened-exchange local density
approximation. Details of the formalism, which is based on the method of
Massidda, Posternak, and Baldereschi [Phys. Rev. B 48, 5058 (1993)] for the
unscreened Hartree-Fock exchange are given. The results for the
transition-energy and structural properties of several test cases are
presented. Results of calculations of the Cu electric-field gradient in Cu2O
are also presented, and it is shown that the hybrid functionals are much more
accurate than the standard local-density or generalized gradient
approximations
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