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Calibration of a semi‐empirical procedure for predicting the ground‐state spin multiplicities of open‐shell molecules. Applications to new systems
Author(s) -
Ichimura Andrew S.,
Koga Noboru,
Iwamura Hiizu
Publication year - 1994
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610070407
Subject(s) - chemistry , nitrene , multiplicity (mathematics) , ground state , open shell , nitroxide mediated radical polymerization , molecule , network topology , calibration , spin (aerodynamics) , computational chemistry , topology (electrical circuits) , statistical physics , molecular physics , thermodynamics , atomic physics , organic chemistry , quantum mechanics , physics , polymer , computer science , engineering , catalysis , mathematical analysis , mathematics , radical polymerization , copolymer , electrical engineering , operating system
A semi‐empirical configuration interaction (CI) algorithm is presented for predicting the ground‐state spin multiplicity of open‐shell systems. The computed energy gaps Δ E (LSHS) of model systems, Y‐phenyl‐X‐phenyl‐Y, where Y is a nitrene or nitroxide radical and X is an exchange coupling unit, are critically compared with the available experimental data. The current method has attenuated the deficiencies of the earlier algorithm proposed by Lahti and Ichimura and the predictions are qualitatively clearer, facilitating the classification of high‐ and low‐spin topologies for isomeric species. The relative effectiveness of different exchange couplers can be discerned semi‐quantitatively, and several new exchange couplers are described. The reasons for the qualitative failure of the earlier algorithm are discussed.