Spin-adapted coupled-cluster theory for the treatment of low-spin open-shell states

为了扩展耦合团簇理论在量子化学(多参考)情况下的适用性，提出了一种新的计算方法。最初的重点将放在需要至少两个参考行列式的开壳单重态(即双自由基)上。基于薛定谔方程和自旋本征值方程在激发态函数上的投影，提出了一种自旋自适应方案。对于化学应用，将开发一种计算机程序，允许有效地计算分子能量和性质。

To extend the applicability of coupled-cluster theory in quantum chemical (multi-reference) cases is proposed. The initial focus will be on open-shell singlet states (i.e. biradicals) requiring at least two reference determinants. A spin-adapted scheme is suggested based on the projection of Schrödinger and spin eigenvalue equations onto excited configuration functions. For chemical applications, a computer program will be developed that allows the efficient computation of molecular energies and properties.