ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Computational Chemistry and Molecular Modeling
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 47 (1993), S. 405-423 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A numerical method is developed to obtain sequences of functions converging to the eigenfunctions of a Schrödinger operator in the Hilbert space L2(-∞, ∞), whose norm is used to introduce the criterion of convergence in the norm and we show that it guarantees the accurate computation of expected values of a symmetric operator. The method consists in solving the Dirichlet problem associated to the eigenvalue problem in the interval [-n, n] by the Ritz method, whose convergence to both eigenvalues and eigenfunctions is guaranteed by the compactness criterion. Using the asymptotic perturbation theory in L2(-∞, ∞), we prove the convergence of both eigenvalues and eigenfunctions of the Dirichlet problem to those of the unbounded system when the interval [-n, n] is expanded. The method is applied to the harmonic oscillator, the Mitra potential, as well as to the potential V(r) = r and the Coulomb and Yukawa potentials; in each case, the convergence of eigenvalues and eigenfunctions is shown. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 53 (1995), S. 27-35 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By means of examples, Löwdin showed that L2 convergence of approximate wave functions ψn to the exact ψ using the single limit limn→∞〈ψn, Aψn〉 = 〈ψ,Aψ〉 is not sufficient to compute accurate expectation values. It is shown that L2 convergence is indeed a sufficient condition to compute accurate expectation values using iterated limits limm→∝ limn→∝〈ψn, Aψm〉 = 〈ψ, Aψ〉 instead of a single limit. Practical conditions that guarantee the stability of single-limit calculations are given. It is also shown that the L2 covergence of wave functions implies the convergence in the L1(R3)-norm of their corresponding densities. This permits us to prove Weinhold's conjecture that the rate of convergence of densities are greater than that of wave functions. The results are extended to the momentum space, and their equivalence with those of position space is shown. Properties of Lp spaces are used to introduce the Cauchy criterion that permits us to check the convergence in norm of approximate wave functions and their densities, as well as to estimate exact errors. This is illustrated by a numerical example. © 1995 John Wiley & Sons, Inc.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 241-250 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work we present a mathematical formulation of the physical fact that the bound states of a quantum system confined into a box Ω (with impenetrable walls) are similar to those of the unconfined system, if the box Ω is sufficiently large, and it is shown how the bound states of atomic and molecular Hamiltonians can be approximated by those of the system confined for a box Ω large enough (Dirichlet eigenproblem in Ω). Thus, a method for computing bound states is obtained which has the advantage of reducing the problem to the case of compact operators. This implies that a broad class of numerical and analytic techniques used for solving the Dirichlet problem, may be applied in full strength to obtain accurate computations of energy levels, wave functions, and other physical properties of interest. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 50 (1994), S. 113-134 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method developed previously for computing eigenfunctions of one-dimensional Schrödinger operators is extended to Schrödinger operators in L2(R3N). It is known that in many cases these operators have not a compact resolvent; therefore, the convergence in L2(R3N) of the more used methods for computing the eigenfunctions is not guaranteed. The idea of the present method consists of replacing the eigenvalue problem in L2(R3N) by one corresponding to the system confined into a box Ω with impenetrable walls [Dirichlet problem in L2(Ω)]. It is shown that the eigenfunctions of the unbounded system can be approximated by those of the confined system when the box Ω is expanded. On the other hand, it is proved that the Schrödinger operator associated to the confined system has a compact resolvent and its corresponding sesquilinear form is bounded and elliptic in the Sobolev space W2,10(Ω). These properties guarantee the convergence in L2(Ω) of the standard methods to solve the Dirichlet problem: the Ritz method as well as the finite-element and finite-difference methods. Therefore, the eigenfuncions of the unbounded system can be approximated in L2(R3N) by means of the numerical solutions of the Dirichlet problem in L2(Ω) with sufficiently large Ω. This property guarantees the accurate computation of the true expectation values. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 57-77 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A numerical method is developed to obtain a sequence of functions converging to the eigenfunctions of the Schrödinger operator H = - ½ Δ + V(r) for V(r) = - Z/r + χ(r), where χ(r) is a continuous and bounded-from-below function for (r ∊ 0, ∞). The criterion of convergence in the convergence in the norm of the Hilbert space L2(0, ∞), which assures the accurate computation of the expected values for a symmetric operator, as we show. The method consists of solving the dirichlet problem inside a box of radius n by the Ritz method, whose convergence in the norm is proved using the compactness criterion. Using a physical argument, we show that the bounded states of the Dirichlet problem converge to those the unbounded system in the norm of L2(0, ∞) as n grows. The method is applied to the potentials V(r) = - Z/r + ari (i ≥ 0) and V(r) = - Z/r + a/(1 + rλ); in each case, we show the numerical convergence of eigenfunctions, energies, and density moments. © 1994 John Wiley & Sons, Inc.
    Additional Material: 14 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 53 (1995), S. 15-25 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recently, it was proven that the wave functions ψ of one-dimensional Schrödinger operators can be approximated by those ψn corresponding to the Dirichlet eigenproblem in a finite box sufficiently large. In this article, sufficient conditions to compute expectation values are used to prove that the expectation value 〈ψ, Sψ〉 can be approximated by 〈ψn, Sψn〉 as n → ∞, for a wide class of unbounded symmetric operators S. © 1995 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996), S. 1077-1096 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The role of the asymptotic behavior of approximating sequences of electron densities ρn(r) in the calculation of one-electron properties is studied. Rigorous mathematical results in the frame of Hilbert spaces are used to prove the following facts: (i) Both the L2 convergence of wave functions ψn and the E convergence of the corresponding energies En guarantee the correctness of the limiting procedure limn→x ∫Ω s((overline)x(/overline)|ψn|2 d(overline)x(/overline) = ∫Ω s((overline)x(/overline))|ψ|2 d(overline)x(/overline) for the most frequently used operators s(x), Ω being any bounded region of the n-particle configuration space R3N; and (ii) the uniform boundedness of the sequence {ρn} together with both the L2 and E convergencies is sufficient to guarantee the correctness of the limiting procedure limn→x ∫∞0 s(r)ρnr2dr = ∫x0 s(r)ρr2 dr for most one-electron operators s(r) including the power moment operators rk which, for large k, are representative of the class of operators not relatively form-bounded by the Hamiltonian. The mathematical concept of uniform boundedness is used to give a characterization of the capability of {ρn} to reproduce the asymptotic behavior of the true electron density ρ and it is shown by means of numerical examples how a sequence {ρn} that does not reproduce the correct asymptotic behavior is not uniformly bounded and can give divergent expectation values of one-electron operators s(r) not relatively form-bounded by the Hamiltonian. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...