Ground and low‐lying excited C2v states of FeO2—A challenge to computational methods

Abstract

AbstractDFT (BPW91 and B3PW91), CCSD, CCSD(T), and MP2 geometry optimizations were performed on the lowest A1, A2, B1, and B2 singlet to septet states (a total of 16 states) of FeO2, 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 3B1 or 5B2, 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 FeO2. The full CI estimate (including Davidson correction and energy extrapolation to 0 μh) gave 3A1 as the lowest state, followed by 5B2 (0.03 eV) and 3B1 (0.06 eV). Both 3B1 and 3A1 have geometries and vibrational frequencies consistent with the observed IR spectrum. The calculated adiabatic electron affinity of FeO2 (from 3B1 of FeO2 to 4B2 of FeO) 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