Basis set and electron correlation effects on the polarizability and second hyperpolarizability of model open-shell π-conjugated systems

2005 ◽  
Vol 122 (11) ◽  
pp. 114315 ◽  
Author(s):  
Benoît Champagne ◽  
Edith Botek ◽  
Masayoshi Nakano ◽  
Tomoshige Nitta ◽  
Kizashi Yamaguchi
Keyword(s):  
Electron Correlation ◽  
Open Shell ◽  
Basis Set ◽  
Correlation Effects ◽  
Second Hyperpolarizability ◽  
Conjugated Systems ◽  
Electron Correlation Effects

Nonnuclear Maxima in the Charge Density

1993 ◽  
Vol 48 (1-2) ◽  
pp. 127-133 ◽  
Author(s):  
Kenneth E. Edgecombe ◽  
Vedene H. Smith, Jr. ◽  
Florian Müller-Plathe
Keyword(s):  
Charge Density ◽  
Electron Density ◽  
Electron Correlation ◽  
Basis Set ◽  
Valence Shell ◽  
Correlation Effects ◽  
Electron Correlation Effects

Abstract Basis-set and electron-correlation effects on the appearance and disappearance of nonnuclear maxima in the electron density are examined in Li2 , Na2 , Na4 and Na5 . It is shown that nonnuclear attractors can be removed in all cases except Li2 . The appearance of a pseudoatom in a lithium molecule correlates remarkably well with the size of the region, in an atomic calculation, of V2r(r) for the valence shell of the atom. This and the fact that the pseudoatom is also present in the promolecule indicate that the pseudoatoms are remnants of, or in fact are portions of, atoms that are not perturbed enough in the molecule to remove an essentially atomic characteristic.

One-proton and multiproton hydrogen bonds between ammonium ions and hydrogen fluoride

1985 ◽  
Vol 63 (7) ◽  
pp. 1562-1567 ◽  
Author(s):  
Henryk T. Flakus ◽  
Russell J. Boyd
Keyword(s):  
Hydrogen Fluoride ◽  
Electron Correlation ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Correlation Effects ◽  
Ammonium Ions ◽  
Electron Correlation Effects ◽  
The One ◽  
Bonded Complexes ◽  
Hydrogen Bonded

Extensive abinitio molecular orbital calculations are reported for the hydrogen bonded complexes of the formula [Formula: see text] and, [Formula: see text] where m = 0, 1, 2, and 3. The one-proton ("linear") hydrogen bonded complexes of the ammonium ions and hydrogen fluoride are predicted to be more stable by about 1 or 2 kcal/mol than the two- and three-proton ("bent") complexes. Several systematic trends and a number of differences between the neutral and protonated series of complexes are observed. The basis set dependence of the results, basis set superposition errors and electron correlation effects are discussed.

Simplified Non-Empirical Unrestricted Hartree-Fock Approximation (SUHF) for the Calculation of Electronic Ground State Properties of Molecules with Closed and Open Valence Shells. I. Method

1993 ◽  
Vol 48 (7) ◽  
pp. 829-833
Author(s):  
Wolfhard Koch
Keyword(s):  
Electron Correlation ◽  
Ground State ◽  
Atomic Orbital ◽  
Closed Shell ◽  
Open Shell ◽  
Polyatomic Molecules ◽  
Correlation Effects ◽  
Hartree Fock ◽  
Electron Correlation Effects ◽  
Electronic Ground

Abstract Focusing on relative stabilities of electronic states with different spin multiplicities of polyatomic molecules, a simplified unrestricted Hartree-Fock (SUHF) procedure is described. Using different orbitals for different spins (DODS), electron correlation effects of both closed-shell and open-shell systems are expected to be taken into account in the simplest way. While working within a symmetrically orthogonalized (Löwdin) basis we make use of the NDDO approximation (neglect of diatomic differential overlap) concerning the evaluation of electron repulsion and nuclear attraction integrals. Originally, a locally orthogonalized all-electron atomic orbital set of Slater type is considered. The approximation method is completely non-empirical. Rotational invariance is fully retained.

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