In the present work we propose two distinct state-averaging (SA)-based methodologies for the calculation of excited states, in conjunction with the long-range complete active space self-consistent fie...

We present an efficient two-level strategy to accelerate the solution of the CASSCF linear-response eigenvalue problem using a customized Davidson algorithm. By identifying a subset of important response-vector components─the so-called P space─we compute and diagonalize full Hessian and metric matrix elements while treating the remaining Q-space components with a diagonal approximation. This approach decouples the orbital and configuration responses, enabling independent preconditioning of each component. Computational cost is further reduced through the resolution-of-the-identity approximation. We demonstrate significant performance gains across a diverse set of molecules, achieving speedups of up to 2.05 compared to the standard diagonal preconditioning. The largest efficiency gains are observed for MCTDA calculations involving many excited states and relatively small response-vector lengths. The two-level strategy is available in ORCA 6.1 and paves the way for extensions to dynamic polarizabilities, which require solving large-scale linear equations, as well as to time-dependent density functional theory and CI singles.

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.

Why do near-identical Fe(III)-azido complexes exhibit different photoreactivity profiles? Linking spin states and key normal modes to wavelength-dependent photoreductive and photooxidative reaction p...

Charlotte Froese Fischer. Ciencias de la computación. Matemáticas. Química computacional. Método de campo autoconsistente multiconfiguracional CASSCF.

Charlotte Froese Fischer. Ciencias de la computación. Matemáticas. Química computacional. Método de campo autoconsistente multiconfiguracional CASSCF.

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This study presents the first-ever investigation of spin-phonon coupling mechanisms in fullerene-based single-molecule magnets (SMMs) using ab initio CASSCF combined with DFT calculations. While lanth...

Strongly correlated electrons can be treated with a configuration interaction of Slater determinants grouped by number of unpaired electrons with exponential cost. The first two papers in this series ...

A combined theoretical/experimental study of the photoreactivity of two flavylium-derived chalcones, 2,4,4′-trihydroxychalcone and 2,4′-dihydroxychalcone, at the multiconfigurational wavefunction leve...

We report the synthesis, crystal structure, spectroscopic and computational electronic structural characterization of two copper corroles, [Cu(5,15-bis(4-methylcarboxyphenyl)-10-(2-methylcarboxyphenyl...