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Development of approximately spin projected energy derivatives for biradical systems
Author(s) -
Kitagawa Y.,
Saito T.,
Nakanishi Y.,
Kataoka Y.,
Matsui T.,
Kawakami T.,
Okumura M.,
Yamaguchis K.
Publication year - 2010
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.22883
Subject(s) - singlet state , spin (aerodynamics) , molecule , chemistry , projection (relational algebra) , quantum , computational chemistry , atomic physics , physics , quantum mechanics , excited state , mathematics , thermodynamics , organic chemistry , algorithm
In this article, we summarize a recent progress in our spin‐projected energy derivative method for broken‐symmetry (BS) solutions of singlet biradical systems. Because, the spin projection procedure that is based on the approximate spin projection (AP) method does not involve a spin contamination error, it improves the accuracy of an optimized geometry and a calculated vibrational frequency for the singlet biradical molecule with the low cost of computation. To examine the spin contamination error in the BS energy derivatives and to demonstrate the efficiency of the AP method, we carry out the geometry optimization and the vibrational calculation of singlet CR 2 (R = H, F, and CH 3 ) molecules that are the typical singlet biradical systems. The results indicate that the error in the singlet CH 2 and C(CH 3 ) 2 molecules are serious, however, the error in the singlet CF 2 molecule, which has electron withdrawing fluorine atoms is negligible. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010