  Properly spin-adapted coupled-cluster theory for general open-shell
configurations remains an elusive goal in electronic structure theory. In this
contribution we examine Lindgren's normal-ordered exponential ansatz using
spin-free excitation operators, with the aid of automatic equation generation
software. We present a size-extensive reformulation of the unlinked working
equations, and analyse the performance of the method with single and double
excitations for simple molecular systems in terms of accuracy and size
consistency.
