Nonorthogonal Natural Orbitals from Open‐Shell Configuration‐Interaction Calculations

1969 ◽  
Vol 51 (4) ◽  
pp. 1576-1580
Author(s):  
E. Weltin ◽  
Marie Heaton
Keyword(s):  
Configuration Interaction ◽  
Open Shell ◽  
Natural Orbitals ◽  
Configuration Interaction Calculations

Rational orbitals for two-electron S states

1981 ◽  
Vol 59 (10) ◽  
pp. 1552-1556
Author(s):  
F. W. Birss ◽  
W. den Hertog
Keyword(s):  
Wave Function ◽  
Configuration Interaction ◽  
Orthogonal Transformation ◽  
Open Shell ◽  
Wave Functions ◽  
Natural Orbitals ◽  
S States ◽  
Single Configuration

The concept of rational orbitals is introduced, based upon finding that pair of orbitals which yield the single configuration function which maximally overlaps with a configuration interaction wave function. They are simply obtained from the natural orbitals by an elementary orthogonal transformation and are more appropriate than natural orbitals to analysis of functions for open-shell states. The CI wave functions of a number of lS states of helium are analyzed and the nature of the rational orbitals investigated.

The Importance of Photodissociative Trichloromethanol for Atmospheric Chemistry

2003 ◽  
Vol 68 (12) ◽  
pp. 2297-2308 ◽  
Author(s):  
Max Mühlhäuser ◽  
Melanie Schnell ◽  
Sigrid D. Peyerimhoff
Keyword(s):  
Energy Range ◽  
Excited States ◽  
Atmospheric Chemistry ◽  
Configuration Interaction ◽  
Configuration Interaction Calculations

Multireference configuration interaction calculations are carried out for ground and excited states of trichloromethanol to investigate two important photofragmentation processes relevant to atmospheric chemistry. For CCl3OH five low-lying excited states in the energy range between 6.1 and 7.1 eV are found to be highly repulsive for C-Cl elongation leading to Cl2COH (X2A') and Cl (X2P). Photodissociation along C-O cleavage resulting in Cl3C (X2A') and OH (X2Π) has to overcome a barrier of about 0.8 eV (13A'', 11A'') and 1.2 eV (13A') because the low-lying excited states 11A'', 13A' and 13A'' become repulsive only after elongating the C-O bond by about 0.3 Å.

Modification of HAM/3 excitation energies for ΠΠ* transitions of linear molecules

1980 ◽  
Vol 58 (16) ◽  
pp. 1687-1690 ◽  
Author(s):  
Delano P. Chong
Keyword(s):  
Excitation Energy ◽  
Explicit Expression ◽  
Excited States ◽  
Configuration Interaction ◽  
Excitation Energies ◽  
Carbon Suboxide ◽  
Numerical Examples ◽  
Energy Correction ◽  
Linear Molecules ◽  
Configuration Interaction Calculations

The excitation energies calculated by the HAM/3 procedure for ΠΠ* transitions in linear molecules can be internally inconsistent by as much as ± 0.6 eV. In the recent study by Åsbrink etal., the problem was avoided by adopting Recknagel's expressions and requiring the proper average ΠΠ* excitation energy. In this paper, we trace the small inconsistency back to its origin in HAM/3 theory and derive the analytical expression for the energy correction as well as Recknagel's formulas. Numerical examples studied include all seven linear molecules investigated by Åsbrink etal. The explicit expression for the correction enables us to perform meaningful configuration-interaction calculations on the excited states, as illustrated by the carbon suboxide molecule.

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