State-selective core-optimized spin-coupled theory

The first core-optimized spin-coupled description of excited states is presented, based on the core-optimized spin-coupled theory of Gerratt and co-workers and the state-selective spin-coupled theory of Doggett et al. The approach realizes for excited states, for which Gerratt propounded for the ground state, a fully variational description with a single configuration of nonorthogonal orbitals and core orbitals. The model is applied to the S-1(e) states of Be and to three low-lying states of Be-2(+): X(2)Sigma(u)(+), and 1,2(2)Pi(u). The extension of the model to resonance states and the core-optimization of multi-configurational excited-state wave functions is discussed. (C) 1999 John Wiley & Sons, Inc.