Natural orbitals from single and double excitation configuration interaction wave functions: their use in second‐order configuration interaction and wave functions incorporating limited triple and quadruple excitations

1992 ◽  
Vol 96 (9) ◽  
pp. 6850-6856 ◽  
Author(s):  
Roger S. Grev ◽  
Henry F. Schaefer
Keyword(s):  
Configuration Interaction ◽  
Second Order ◽  
Wave Functions ◽  
Natural Orbitals ◽  
Double Excitation

Composite natural orbitals for configuration interaction method

1988 ◽  
Vol 53 (10) ◽  
pp. 2266-2278 ◽  
Author(s):  
Yuichi Yamamoto ◽  
Takeshi Noro ◽  
Kimio Ohno
Keyword(s):  
Configuration Interaction ◽  
Ground States ◽  
New Method ◽  
Entire System ◽  
Interaction Method ◽  
Configuration Interaction Method ◽  
Excitation Energies ◽  
Natural Orbitals ◽  
Double Excitation ◽  
Ci Calculations

A new method of constructing approximate natural orbitals (NO's) is proposed. A system can usually be regarded as consisting of fragments. The approximate NO's of the entire system are constructed from the NO's of fragments in their ground states. These orbitals are expected to be useful in configuration interaction (CI) calculations of a large system where orbital truncation is necessary. The usefulness of these approximate NO's, which are called composite NO's (CNO's), is demonstrated on C4H6. This molecule may be regarded as a combination of two fragments i.e., C2H4's. Excitation energies calculated by single and double excitation CI with the truncated CNO's (14σ, 7π correlating orbitals) agree reasonably well with those calculated with a full orbital set (37σ, 12π correlating orbitals), while the truncated SCFMO's of the same size give disastrous excitation energies.

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.

NATURAL ORBITALS AND ELECTRON ELASTIC MAGNETIC SCATTERING BY NUCLEI

1996 ◽  
Vol 05 (04) ◽  
pp. 717-724 ◽  
Author(s):  
D.N. KADREV ◽  
A.N. ANTONOV ◽  
M.V. STOITSOV ◽  
S.S. DIMITROVA
Keyword(s):  
Density Fluctuation ◽  
Form Factors ◽  
Wave Functions ◽  
Magnetic Scattering ◽  
Correlation Effects ◽  
Valence Nucleon ◽  
Nucleon System ◽  
Natural Orbitals ◽  
Transverse Form Factor ◽  
Fluctuation Model

Natural orbitals obtained within the coherent density fluctuation model and containing nucleon correlation effects are used to calculate characteristics of the A-nucleon system, such as the electron elastic magnetic scattering form factors. The calculations are performed for nuclei with a doubly-closed core and a valence nucleon in a stretched configuration (j=l+1/2), such as the 17 O and 41 Ca nuclei. It is shown that the calculations of the transverse form factor using natural orbitals improve the agreement with the experimental data in comparison with the case when shell-model single-particle wave functions are used.

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