Applying Generalized Variational Principles to Excited-State-Specific Complete Active Space Self-consistent Field Theory

We employ a generalized variational principle to improve the stability, reliability, and precision of fully excited-state-specific complete active space self-consistent field theory. Compared to previous approaches that similarly seek to tailor this ansatz's orbitals and configuration interaction expansion for an individual excited state, we find the present approach to be more resistant to root flipping and better at achieving tight convergence to an energy stationary point. Unlike state averaging, this approach allows orbital shapes to be optimal for individual excited states, which is especially important for charge-transfer states and some doubly excited states. We demonstrate the convergence and state-targeting abilities of this method in LiH, ozone, and MgO, showing in the latter that it is capable of finding three excited-state energy stationary points that no previous method has been able to locate.

Automated summary

In this study, a generalized variational principle is employed to enhance the stability and convergence of fully excited-state-specific complete active space self-consistent field theory. The proposed method shows better resistance to root flipping and achieves tighter convergence to an energy stationary point. The ability to optimize orbital shapes for individual excited states is especially important for charge-transfer states and some doubly excited states.