A 2p?, 3d? valence bond wave function for the 1B1u state of ethylene

1969 ◽  
Vol 14 (5) ◽  
pp. 363-369 ◽  
Author(s):  
Aage E. Hansen
Keyword(s):  
Wave Function ◽  
Valence Bond

scholarly journals Calculation of dispersion interactions with the geminal-based ring Coupled Cluster Doubles method

2020 ◽  
Vol 139 (9) ◽  
Author(s):  
Á. Margócsy ◽  
Á. Szabados
Keyword(s):  
Wave Function ◽  
Asymptotic Behaviour ◽  
Noble Gas ◽  
Valence Bond ◽  
Coupled Cluster ◽  
Leading Order ◽  
Dispersion Interactions ◽  
Dispersion Energy ◽  
Generalized Valence Bond ◽  
Noble Gas Dimers

Abstract The performance of the recently developed multi-reference extension of ring coupled cluster doubles is investigated for dispersion energy calculations, applied to the generalized valence bond wave function. The leading-order contribution to the dispersion energy is shown to have the correct asymptotic behaviour. Illustrative calculations on noble gas dimers are presented.

The valence bond theory of molecular structure - I. Orbital theories and the valence-bond method

1954 ◽  
Vol 223 (1152) ◽  
pp. 63-79 ◽  
Keyword(s):  
Wave Function ◽  
Valence Bond ◽  
Formal Structure ◽  
Orbital Theory ◽  
Apparent Paradox ◽  
Localized Molecular Orbitals ◽  
Structure Of Molecules ◽  
Large Numbers ◽  
Strong Repulsion ◽  
Mo Theory

The molecular orbital (MO) and valence bond (VB) theories of the electronic structure of molecules emerge from one quite general approximation method involving the use of anti-symmetrized products (AP’s) of one-electron wave function (‘orbitals’), differing funda­mentally only in their choice of a first approximation; in MO theory this is usually a single AP, and the orbitals are non-localized molecular orbitals, but in VB theory it is always a combination of many AP’s, the orbitals being localized atomic orbitals. The MO theory lends itself well to rigorous formal development and has recently been employed in essentially ab initio calculations; but a corresponding development of the existing VB method is precluded by the technical necessity of neglecting large numbers of non-vanishing integrals. The present papers are devoted to a reformulation of the VB method in which the usual difficulties are circumvented; the revised method is no less powerful than an MO approach in which full configuration interaction (i. e. refinement of the wave function by addition of ‘excited state’ AP’s) is admitted. The first paper is essentially preparatory. Orbital theories involving many AP’s are discussed generally but with emphasis on the origin and concepts of the VB approach. Analysis of the charge distribution in a molecule is then shown to provide a unified description of chemical bonding and a general method of defining a 'bond order’, applicable in any orbital theory. Against this background the existing VB theory is critically discussed. The validity of the whole approach rests upon the assumption of approxi­mate orthogonality of the basic orbitals; an attractive method of making the theory rigorous, whilst retaining its formal structure, would therefore involve the use of accurately orthogonal basic orbitals. But a treatment of the hydrogen molecule along such lines leads to an apparent paradox; the formally ‘covalent’ VB structure describes only strong repulsion between the ‘bonded’ atoms. This paradox is resolved and certain general characteristics of the revised VB theory are tentatively inferred.

scholarly journals Resonating valence bond wave function: from lattice models to realistic systems

2005 ◽  
Vol 169 (1-3) ◽  
pp. 386-393 ◽  
Author(s):  
Michele Casula ◽  
Seiji Yunoki ◽  
Claudio Attaccalite ◽  
Sandro Sorella
Keyword(s):  
Wave Function ◽  
Valence Bond ◽  
Lattice Models ◽  
Resonating Valence Bond

scholarly journals Correlated geminal wave function for molecules: An efficient resonating valence bond approach

2004 ◽  
Vol 121 (15) ◽  
pp. 7110-7126 ◽  
Author(s):  
Michele Casula ◽  
Claudio Attaccalite ◽  
Sandro Sorella
Keyword(s):  
Wave Function ◽  
Valence Bond ◽  
Resonating Valence Bond
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