Ligand Field Tuning of Photoreactivity: Contrasting Low‐Spin and High‐Spin Fe(III)‐Azido Complexes 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...

#CASSCF and (TD-)DFT are well-established components of #ORCA's method portfolio. Check out the new paper by Krewald et al., who use both for tuning the photoreactivity of Fe(III)-azido complexes.

doi.org/10.1002/cptc...

CASSCF in ORCA: www.faccts.de/docs/orca/6....

#ORCAqc #CompChem #QuantumChem

The video is up in YouTube! CASSCF with ORCA, merging metal and ligand fragment wavefunctions to retrieve all metal 3d orbitals.
#compchem #chemsyk #CASSCF #Corrole #ORCA

youtu.be/LAm9jEFDjKM

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.

New work is out!
We implemented linear response CASSCF in CFour, powered by the open-source Diaglib solver: we are now able to access absorption spectra & frequency-dependent properties on standard hardware.

doi.org/10.1021/acs....

#compchem #molecolab #casscf @tommasonottoli.bsky.social

A Two-Level Preconditioner for the CASSCF Linear-Response Equations 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.

Hot off the press: “A Two-Level Preconditioner for the CASSCF Linear-Response Equations” by our scientific advisor Benjamin Helmich-Paris (@orca-qc-official.bsky.social). Its already part of ORCA 6.1, check it out!

doi.org/10.1021/acs....

#ORCA #ORCAqc #CompChem #QuantumChem #TheoChem #CASSCF

Impacts of hydroxylation on the photophysics of chalcones: insights into the relation between the chemical composition and the electronic structure 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...

An old article in Theoretical Organic Photochemistry. The multistate reaction manifold includes optimized and characterized conical intersections and intersystem crossings.

pubs.rsc.org/en/content/a...

#conicalintersection #quantum #chemistry #CASSCF #CASPT2 #MOLCAS #compchem #theochem #chemsky

Neutral and Anionic Free-base and Copper Corroles: Structural, spectroscopic and computational analysis and hypercorrole features 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...

New work in anionic #corroles with a healthy dose of #casscf calculations. Thx
@orca-qc-official.bsky.social #chemsky
Neutral and Anionic Free-base and Copper Corroles: Structural, spectroscopic and computational analysis and hypercorrole features | ChemRxiv - doi.org/10.26434/che...

Neodymium(III) Aqua Ion as a Model System in Ab Initio Crystal Field Analysis Beyond Point Charges and Crystal Field Theory | Inorganic Chemistry pubs.acs.org/doi/10.1021/... So̷rensen and co-workers @InorgChem #neodymium #aqua #abinitio #CFT #CASSCF

Dinuclear Rare-Earth β-Diketiminates with Bridging 3,5-Ditert-butyl-catecholates: Synthesis, Structure, and Single-Molecule Magnet Properties pubs.acs.org/doi/10.1021/... Klementyeva, Ruben, Wernsdorfer, Moreno-Pineda, and co-workers @InorgChem #rareearth #diketiminato #SMM #CASSCF