General-Model-Space State-Universal Coupled-Cluster Method: Excited States of Ozone

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Abstract
The low-lying excited states of ozone are investigated using the recently developed general-model-space state-universal coupled-cluster methods and the results are compared with other multireference coupled-cluster and spin-adapted unitary-group coupled-cluster approaches. The role played by the choice of different molecular orbitals in coupled-cluster calculations is also explored. It is found that the low-lying 1,3B2 states are particularly sensitive to the choice of the molecular orbitals. This observation explains some significant differences between the results obtained with spin-adapted and spin-non-adapted multireference coupled-cluster approaches, as documented by earlier studies. The use of appropriate orbitals brings the effect of spin-adaptation to its normal range.