Efficient and accurate local approximations to coupled-electron pair approaches: An attempt to revive the pair natural orbital method

2009 ◽  
Vol 130 (11) ◽  
pp. 114108 ◽  
Author(s):  
Frank Neese ◽  
Frank Wennmohs ◽  
Andreas Hansen
Keyword(s):  
Electron Pair ◽  
Orbital Method ◽  
Natural Orbital ◽  
Local Approximations

A complete basis set model chemistry. IV. An improved atomic pair natural orbital method

1994 ◽  
Vol 101 (7) ◽  
pp. 5900-5909 ◽  
Author(s):  
J. A. Montgomery ◽  
J. W. Ochterski ◽  
G. A. Petersson
Keyword(s):  
Basis Set ◽  
Orbital Method ◽  
Natural Orbital ◽  
Complete Basis ◽  
Atomic Pair ◽  
Complete Basis Set

scholarly journals Electronic spectra of polyatomic molecules I–Saturated aldehydes

1935 ◽  
Vol 149 (868) ◽  
pp. 434-446 ◽  
Keyword(s):  
Electronic Structures ◽  
Hydrogen Molecule ◽  
Electron Pair ◽  
Polyatomic Molecules ◽  
The Other ◽  
Orbital Method ◽  
Atom Pair ◽  
Advantages And Disadvantages ◽  
Lennard Jones ◽  
Pair Method

Of the two methods which are now available to describe the electronic structures of polyatomic molecules, only the more recent—the orbital method—can at present be applied to the excited levels of molecules, and so any interpretation of the spectra of polyatomic molecules must be done in its terms. This method, which was suggested by Lennard-Jones for diatomic molecules and applied to polyatomic molecules by Hund, Mulliken, and Lennard-Jones, starts on the assumption of the symmetry of the nuclear framework; the electrons are then added one by one to orbitals characteristic of the molecule as a whole and not of any particular atom-pair. In this last feature, the method differs from the earlier one developed by Pauling and Slater on the lines of the Heitler-London treatment of the hydrogen molecule, where the electron-pair bond between two atoms is generally assumed. For some purposes the electron-pair method has advantages over the orbital method (an example of the use of the electron-pair method where the other would be inapplicable is given by fennel's recent work on benzene); the advantages and disadvantages of each have been discussed in various papers, and it is probable that they will both be necessary complement of each other for some time in the elucidation of any particular problem.

Bipolaron Formation in B12 and (B11C)+ Icosahedra

1987 ◽  
Vol 97 ◽  
Author(s):  
I. A. Howard ◽  
C. L. Beckel ◽  
David Emin
Keyword(s):  
Total Energy ◽  
Electronic Transport ◽  
Electron Pair ◽  
Positive Charge ◽  
Energy Difference ◽  
Energy Reduction ◽  
Orbital Method ◽  
Molecular Orbital Method ◽  
Icosahedral Clusters ◽  
Self Consistent

ABSTRACTBoron carbides, B1-xCx with 0.085 ≤ × ≤ 0.200, generally contain both B12 and B11C icosahedra. However, the electronic transport with 0.1 ≤ × ≤ 0.2 is believed to occur by means of bipolaron hopping between only B11 C icosahedra [i]. We have calculated the changes in energy, atomic positlions and charge distribution when a pair of electrons is added to the isoelectronic icosahedral clusters B12 and (B11C)+. We simulate an icosahedron in a neutral lattice by bonding the icosahedral atoms to hydrogenic atoms which we constrain to be neutral. The computations are performed with a self-consistent molecular-orbital method, PRDDO.We find a total energy reduction of -3.7 eV for two electrons added to a B12 icosahedron. Of this, -2.7 eV arises from the electrons filling the icosahedron's bonding orbitals. The remaining -1.0 eV comes from the contraction of the icosahedron's radius by -0.09 Å. For two electrons added to a (B11C)+ icosahedron we find a total energy reduction of -18.2 eV. Of this, -16.5 eV arises from filling the icosahedron's bonding orbitals. The remainder arises frop a -0.09 Å contraction of the icosahedron's radius. Thus, we find (B11C) icosahedra to be strongly energetically favored over B12 icosahedra as bipolaron sites.The positive charge associated with a (B11C)+ icosahedron is distributed over the eleven boron atoms. Concomitantly, we find the added two electrons of the bipolaron to be distributed over all twelve sites of the B11C icosahedron. We find the energy difference between an electron pair added to B12 and (B11C)+ icosahedra to arise principally from the increased Coulomic attraction provided by the extra positive charge of the (B11C) icosahedron.

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