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Ground and low‐lying excited C 2 v states of FeO 2 —A challenge to computational methods
Author(s) -
Grein Friedrich
Publication year - 2008
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.21855
Subject(s) - basis set , adiabatic process , atomic physics , chemistry , extrapolation , excited state , excitation , order (exchange) , singlet state , state (computer science) , multireference configuration interaction , ground state , physics , configuration interaction , computational chemistry , quantum mechanics , mathematics , density functional theory , mathematical analysis , finance , algorithm , economics
DFT (BPW91 and B3PW91), CCSD, CCSD(T), and MP2 geometry optimizations were performed on the lowest A 1 , A 2 , B 1 , and B 2 singlet to septet states (a total of 16 states) of FeO 2 , using in most cases the 6‐311+G(3df) basis set. With few exceptions, the different methods led to similar geometries. The lowest state is 3 B 1 or 5 B 2 , depending on the method used. The quality of the various computational methods was tested by a comparison of vertical excitation energies with corresponding high‐level MRCI values. The best agreement with MRCI was found for BPW91 and B3PW91, with average deviations of about 0.2 eV. MRCI calculations were carried to extremely low configuration selection thresholds (0.025 μh) in order to find the lowest state of FeO 2 . The full CI estimate (including Davidson correction and energy extrapolation to 0 μh) gave 3 A 1 as the lowest state, followed by 5 B 2 (0.03 eV) and 3 B 1 (0.06 eV). Both 3 B 1 and 3 A 1 have geometries and vibrational frequencies consistent with the observed IR spectrum. The calculated adiabatic electron affinity of FeO 2 (from 3 B 1 of FeO 2 to 4 B 2 of FeO 2 − ) is 2.46 eV with CCSD(T), and 2.22 eV with BPW91, compared with the experimental value of 2.36 eV. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009