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Combination of approximate spin‐projection and spin‐restricted calculations based on ONIOM method for geometry optimization of large biradical systems
Author(s) -
Kitagawa Y.,
Yasuda N.,
Hatake H.,
Saito T.,
Kataoka Y.,
Matsui T.,
Kawakami T.,
Yamanaka S.,
Okumura M.,
Yamaguch K.
Publication year - 2012
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.24018
Subject(s) - oniom , energy minimization , spin (aerodynamics) , chemistry , geometry , projection (relational algebra) , ion , bond length , molecule , computational chemistry , molecular physics , physics , thermodynamics , mathematics , algorithm , organic chemistry
In this article, we combine the approximate spin projection (AP) and the spin‐restricted (R) calculations based on ONIOM method for a geometry optimization of large biradical systems such as polynuclear metal complexes. This two‐layer quantum mechanics/quantum mechanics′ (QM/QM′) (AP/R) method treats atoms of an inner layer around the spin sources with the AP method, whereas the whole atoms including the peripheral ligands are calculated by the R method. The AP/R method is applied for the geometry optimizations of chromium(II) ions in Cr 2 (O 2 CCH 3 ) 4 (OH 2 ) 2 ( 1 ) and Cr 2 {O 2 CPh(CHMe 2 ) 3 } 4 ( 2 ) complexes that involve quadruple CrCr bonds. The optimized structural parameters indicate that the error of the two‐layer combination is smaller than 0.01 Å in the optimized CrCr bond length on both complexes. The error is only 12.3% of the spin contamination error and 1.7% of the static correlation correction in the complex 1 . The error of the two‐layer combination in a total energy is also estimated to be lower than 1 kcal mol −1 in both complexes. © 2012 Wiley Periodicals, Inc.