Journal ArticleDOI
Spin projected extended Hartree--Fock equations
István Mayer,J. Ladik,G. Biczó +2 more
TLDR
In this article, the spin projected Hartree-Fock equations are derived and discussed in the general (many λi) case, based on the corresponding generalized Brillouin theorem, substituting in its expression a spin projected DODS Slater determinant as a linear combination of determinants.Abstract:
The (spin projected) extended Hartree-Fock equations are derived and discussed in the general (“many λi”) case. The derivation is based on the corresponding generalized Brillouin theorem, substituting in its expression the spin projected DODS Slater determinant as a linear combination of determinants. The expressions obtained for the elements of the different matrices ecd (c = a or b, and d = a or b) occurring in the equations are analyzed. The transformation of the equations into the form of a pseudoeigenvalue problem and the LCAO form of the equations are given, too. Finally the relation to the Goddard's GF equations is discussed in detail.read more
Citations
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Journal ArticleDOI
Projected Hartree–Fock theory
TL;DR: In this article, the authors derive and implement a "variation after projection" PHF theory, which can be applied to both collinear and non-collinear spin cases, and can be used in conjunction with deliberate symmetry breaking and restoration of other molecular symmetries like complex conjugation and point group.
Book ChapterDOI
The Spin-Projected Extended Hartree-Fock Method
TL;DR: The spin-projected extended Hartree-Fock (HF) method as discussed by the authors is the basic one in quantum chemistry and has been applied to many-electron wave functions.
Journal ArticleDOI
Projected Hartree-Fock Theory
TL;DR: This work derives and implements a "variation after projection" PHF theory using techniques different from those previously employed in quantum chemistry, and presents several benchmark applications to dissociation curves and singlet-triplet energy splittings, showing that the resulting PHF wavefunctions are of high quality multireference character.
Journal ArticleDOI
Restricted Ensemble-Referenced Kohn-Sham versus Broken Symmetry Approaches in Density Functional Theory: Magnetic Coupling in Cu Binuclear Complexes †
TL;DR: It would be possible to develop improved density functionals which will allow for a rigorous treatment of open shell systems in density functional theory.
Journal ArticleDOI
Density functional theory: Foundations reviewed
TL;DR: In this paper, a broad range of issues lying at the foundations of Density Functional Theory, DFT, are reviewed, and the possibility of improving DFT functionals by applying in a systematic way the N -representability conditions on the second-order reduced density matrix (2-RDM) has been discussed.
References
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Journal ArticleDOI
Quantum Theory of Many-Particle Systems. I. Physical Interpretations by Means of Density Matrices, Natural Spin-Orbitals, and Convergence Problems in the Method of Configurational Interaction
TL;DR: In this article, the authors define a set of generalized density matrices for the Hermitean density matrix of order $k, which is further antisymmetric in each set of these indices.
Book ChapterDOI
Molecular Orbital Theory
TL;DR: In this paper, the problem of reducing molecular orbital calculations to expressions involving one-and two-electron integrals over the spatial coordinates, with coefficients determined by the group theoretical properties of the spin functions and the electronic permutations, is addressed.
Journal ArticleDOI
Band Theory, Valence Bond, and Tight‐Binding Calculations
TL;DR: In this article, it is shown that a large part of the correlation error can be removed by permitting different orbitals for different spins, which leads to a scheme intermediate between band theory and valence bond method and, by means of a single parameter, one can obtain an essential lowering of the energy curve and the correct asymptotic behavior for separated atoms or constituents.