Combination of approximate spin‐projection and spin‐restricted calculations based on ONIOM method for geometry optimization of large biradical systems. Issue 3 (13th February 2012)

• Record Type: Journal Article
• Authors: Kitagawa, Y.; Yasuda, N.; Hatake, H.; Saito, T.; Kataoka, Y.; Matsui, T.; Kawakami, T.; Yamanaka, S.; Okumura, M.; Yamaguch, K.; Nakai, Hiromi; Yoshizawa, Kazunari; Ando, Koji; Nakajima, Takahito; Brändas, Erkki J.
• Is Part Of: International journal of quantum chemistry. Volume 113:Issue 3(2013:Feb. 05)
• Page Start: 290
• Page End: 295
• Publication Date: 2012-02-13
• Subjects: Quantum chemistry -- Periodicals; 541.28
• DOI: 10.1002/qua.24018
• Languages: English
• ISSNs: 0020-7608

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>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 Cr₂(O₂CCH₃)₄(OH₂)₂ (<bold>1</bold>) and Cr₂{O₂CPh(CHMe₂)₃}₄ (<bold>2</bold>) complexes that involve quadruple CrCr bonds. The optimized structural parameters indicate that the error of the two‐layer combination is smaller than 0.01 Å in the optimized CrCr 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 <bold>1</bold>. 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.</p> </abstract>