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Journal ArticleDOI

Virtual orbitals in hartree--fock theory.

01 May 1970-Physical Review A (American Physical Society)-Vol. 1, Iss: 5, pp 1285-1288
TL;DR: In this paper, an arbitrariness of virtual orbitals in the Hartree-Fock theory is discussed, and it is explicitly demonstrated that the energy spectrum of the virtual orbits can be manipulated so that the convergence property may be improved in the perturbation theory and the configuration interaction calculation.
Abstract: An arbitrariness of virtual orbitals in the Hartree-Fock theory is discussed, and it is explicitly demonstrated that the energy spectrum of the virtual orbitals can be manipulated so that the convergence property may be improved in the perturbation theory and the configuration interaction calculation based on the Hartree-Fock equation
Citations
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Journal ArticleDOI
TL;DR: A simple algorithm, which is called the maximum overlap method (MOM), for finding excited-state solutions to self-consistent field (SCF) equations that maximizes the overlap between the occupied orbitals on successive SCF iterations to prevent variational collapse to the ground state.
Abstract: We present a simple algorithm, which we call the maximum overlap method (MOM), for finding excited-state solutions to self-consistent field (SCF) equations. Instead of using the aufbau principle, the algorithm maximizes the overlap between the occupied orbitals on successive SCF iterations. This prevents variational collapse to the ground state and guides the SCF process toward the nearest, rather than the lowest energy, solution. The resulting excited-state solutions can be treated in the same way as the ground-state solution and, in particular, derivatives of excited-state energies can be computed using ground-state code. We assess the performance of our method by applying it to a variety of excited-state problems including the calculation of excitation energies, charge-transfer states, and excited-state properties.

440 citations

Journal ArticleDOI
TL;DR: In this paper, a diagrammatic many-body perturbation theory is formulated through third order and applied to LiH, BH, and HF with various sizes of two-center Slater orbital basis sets.
Abstract: Diagrammatic many‐body perturbation theory is formulated through third order and applied to LiH, BH, and HF with various sizes of two‐center Slater orbital basis sets. The most extensive calculations use 46 orbitals to recover 94, 95, and 97% of the experimental correlation energy for the three molecules, respectively, when the perturbation expansion is carried through third order with pair restrictions and including selections of higher‐order diagrams via denominator shifts. A detailed analysis of the ’’pair’’ correlation energies relative to SCF occupied orbitals is given, including both inter‐ and intrapair contributions for the different spin cases.

323 citations

Journal ArticleDOI
TL;DR: A series of molecular applications of many-body perturbation theory (MBPT) and the coupled-cluster doubles (CCD) model are described in this paper, including correlation energies, including contributions from single, double, and quadruple excitations diagrams in fourth-and higher-order; dissociation energies; potential energy surfaces; and molecular polarizabilities and hyperpolarizabilities.
Abstract: A series of molecular applications of many-body perturbation theory (MBPT) and the coupled-cluster doubles (CCD) model are described. Even though these methods have been available for sometime, only recently have large scale, MBPT molecular calculations become available. In the case of CCD, the results presented here are among the first obtained from a general purpose ab initio program. The intention of this paper is to present an overview of the current state of the many-body approach to ground state properties of molecules. The properties studied are correlation energies, including contributions from single, double, and quadruple excitations diagrams in fourth-and higher-order; dissociation energies; potential energy surfaces; and molecular polarizabilities and hyperpolarizabilities. Examples are taken from studies of a variety of molecules including HF, H2O, HCO, C6H6, B2H6, CO2, and N2. In many cases, it is found that quantitatively accurate dissociation energies, geometries, and force constants can be obtained. In an illustration of the X1Σg+ potential energy curve of N2, it is shown that a single UHF or RHF reference function MBPT/CCD approach is inadequate at some internuclear separation.

322 citations

Journal ArticleDOI
TL;DR: A comprehensive review of photoionization of rare gas atoms using monochromatized synchrotron radiation is given in this paper, with a focus on the general experimental and theoretical background.
Abstract: A comprehensive review is given on photoionization of rare gas atoms using monochromatized synchrotron radiation. Emphasis is put upon the general experimental and theoretical background, and illustrative examples are presented in order to show the present status and the progress in the field during the last decade.

285 citations

Book ChapterDOI
01 Jan 1977
TL;DR: The correlation energy as mentioned in this paper is defined as the difference between the Hartree-Fock (HF) limit energy and the exact solution of the nonrelativistic Schrodinger equation.
Abstract: As the scope of quantum chemistry broadened from the consideration of stable molecules near equilibrium to encompass potential curves and surfaces, transition states, radicals, ions, and excited states, the shortcomings of the Hartree— Fock (HF) approximation for the description of the electronic structure of molecular systems became increasingly evident. The energy error of the restricted HF wave function, i.e., the difference between the HF limit energy (which is the limit approached by restricted self-consistent field calculations as the basis set approaches completeness) and the exact solution of the nonrelativistic Schrodinger equation, has been termed the correlation energy.(1) It reflects the fact that the HF Hamiltonian contains the average, rather than instantaneous, interelectron potential, and thus neglects the correlation between the motions of the electrons.

285 citations