PNO–CI (pair natural‐orbital configuration interaction) and CEPA–PNO (coupled electron pair approximation with pair natural orbitals) calculations of molecular systems. III. The molecules MgH2, AlH3, SiH4, PH3 (planar and pyramidal), H2S, HCl, and the Ar atom

1975 ◽  
Vol 63 (1) ◽  
pp. 455-463 ◽  
Author(s):  
R. Ahlrichs ◽  
F. Keil ◽  
H. Lischka ◽  
W. Kutzelnigg ◽  
V. Staemmler
Keyword(s):  
Configuration Interaction ◽  
Electron Pair ◽  
Pair Approximation ◽  
Natural Orbital ◽  
Natural Orbitals ◽  
Molecular Systems ◽  
Orbital Configuration

scholarly journals A test of composite natural orbitals for benzene

1992 ◽  
Vol 70 (2) ◽  
pp. 532-536 ◽  
Author(s):  
Yuichi Yamamoto ◽  
Takeshi Noro ◽  
Kimio Ohno
Keyword(s):  
Excited State ◽  
Configuration Interaction ◽  
Benzene Molecule ◽  
Natural Orbital ◽  
Excitation Energies ◽  
Natural Orbitals ◽  
Experimental Values ◽  
Ci Calculations ◽  
Good Agreement

Approximate natural orbitals (NO's) of a larger system can be constructed from the NO's of smaller fragment systems. These orbitals, called composite NO's (CNO's) are expected to be useful in configuration interaction (CI) calculations. The effectiveness of these NO's is shown for the benzene molecule. This molecule is considered a combination of three ethylenes. The CI calculations were carried out for the S1 – S3 and T1 – T3 states. We take into account single and double excitations from σ and π electrons in the CI calculations. The calculated excitation energies are in good agreement with the experimental values Keywords: benzene, π–π* excited state, composite natural orbital, ionic and covalent, SDCI.

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