TY - JOUR
T1 - Hyper Open-Shell States
T2 - The Lowest Excited Spin States of O Atom, Fe2+ Ion, and FeF2
AU - Varga, Zoltan
AU - Verma, Pragya
AU - Truhlar, Donald G.
N1 - Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/9/13
Y1 - 2017/9/13
N2 - Excited spin states are important for reactivity, catalysis, and magnetic applications. This work examines the relative energies of the spin states of O atom, Fe2+ ion, and FeF2 and characterizes their excited spin states. Both single-configuration and multireference methods are used to establish the character of the lowest singlet excited state of all three systems and the lowest triplet excited state of Fe2+ and FeF2. We find that the conventional representation of the orbital occupancies is incorrect in that the states have more unpaired electrons than the minimum number required by their total electron spin quantum number. In particular, we find that, for a given spin state, an electronic configuration with more than 2S unpaired electrons is more stable than the configuration with 2S unpaired electrons (where S is the spin of the system). For instance, triplet FeF2 with four unpaired electrons is lower in energy than triplet FeF2 with two unpaired electrons. Such highly open-shell configurations are labeled as hyper open-shell electronic configurations in this work and are compared to ordinary open-shell or closed-shell electronic configurations. The hyper open-shell states considered in this work are especially interesting because, unlike typical biradicals and polyradicals, the unpaired electrons are all on the same center. This work shows that the conventional perspective on spin-state energetics that usually assumes ordinary open shells for single-centered radicals needs modification to take into account, whenever possible, hyper open-shell configurations as well.
AB - Excited spin states are important for reactivity, catalysis, and magnetic applications. This work examines the relative energies of the spin states of O atom, Fe2+ ion, and FeF2 and characterizes their excited spin states. Both single-configuration and multireference methods are used to establish the character of the lowest singlet excited state of all three systems and the lowest triplet excited state of Fe2+ and FeF2. We find that the conventional representation of the orbital occupancies is incorrect in that the states have more unpaired electrons than the minimum number required by their total electron spin quantum number. In particular, we find that, for a given spin state, an electronic configuration with more than 2S unpaired electrons is more stable than the configuration with 2S unpaired electrons (where S is the spin of the system). For instance, triplet FeF2 with four unpaired electrons is lower in energy than triplet FeF2 with two unpaired electrons. Such highly open-shell configurations are labeled as hyper open-shell electronic configurations in this work and are compared to ordinary open-shell or closed-shell electronic configurations. The hyper open-shell states considered in this work are especially interesting because, unlike typical biradicals and polyradicals, the unpaired electrons are all on the same center. This work shows that the conventional perspective on spin-state energetics that usually assumes ordinary open shells for single-centered radicals needs modification to take into account, whenever possible, hyper open-shell configurations as well.
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U2 - 10.1021/jacs.7b06107
DO - 10.1021/jacs.7b06107
M3 - Article
C2 - 28809102
AN - SCOPUS:85029530757
SN - 0002-7863
VL - 139
SP - 12569
EP - 12578
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 36
ER -