An Efficient and Robust Implementation of CASSCF Linear Response Theory

We present a robust and efficient implementation of linear response theory for a Complete Active Space─Self-Consistent Field wave function. Our approach relies on the Cholesky Decomposition of the two-electron integrals, enabling the routine treatment of large molecular systems on standard hardware. It allows for the computation of both absorption energies and transition properties, as well as frequency-dependent molecular response functions. For both classes of properties, numerically stable and efficient algorithms have been developed. The capabilities of our implementation are demonstrated through the calculation of absorption spectra and molecular response properties of large systems with extended basis sets.