This article describes the philosophy behind- and new features in the ORCA quantum chemistry program suite, version 6.0.

In this work, we describe the development of a new algorithm for the computation of Coulomb-type matrices using the well-known resolution of the identity (RI) or density fitting (DF) approximation. The method is linear-scaling with respect to system size and computationally highly efficient. For small molecules, it performs almost as well as the Split-RI-J algorithm (which might be the most efficient RI-J implementation to date), while outperforming it for larger systems with about 300 or more atoms. The method achieves linear scaling through multipole approximations and a hierarchical treatment of multipoles. However, unlike in the fast multipole method (FMM), the algorithm does not use a hierarchical boxing algorithm. Rather, close-lying objects like auxiliary basis shells and basis set shell pairs are grouped together in spheres that enclose the set of objects completely, which includes a new definition of the shell-pair extent that defines a real-space radius outside of which a given shell pair can be safely assumed to be negligible. We refer to these spheres as “bubbles” and therefore refer to the algorithm as the “Bubblepole” (BUPO) algorithm, with the acronym being RI-BUPO-J. The bubbles are constructed in a way to contain a nearly constant number of objects such that a very even workload arises. The hierarchical bubble structure adapts itself to the molecular topology and geometry. For any target object (shell pair or auxiliary shell), one might envision that the bubbles “carve” out what might be referred to as a “far-field surface”. Using the default settings determined in this work, we demonstrate that the algorithm reaches submicro-Eh and even nano-Eh accuracy in the total Coulomb energy for systems as large as 700 atoms and 7000 basis functions. The largest calculations performed (the crambin protein solvated by 500 explicit water molecules in a triple-ζ basis) featured more than 2000 atoms and more than 33,000 basis functions.

Bernardo de Souza (2025) Highlighted by Jan Jensen If you want to predict accurate reaction energies and barrier heights of typical organic ...

In this work, we propose a new Global Optimization Algorithm (GOAT) for molecules and clusters of atoms and show how it can find the global energy minima for both systems without resorting to molecul...

We present a new fully-automated computational workflow for the calculation of electron ionization mass spectra by automated reaction network discovery, transition state theory and Monte-Carlo simulat...

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All recordings from the ORCA workshop at the Virtual Winter School on Computational Chemistry 2025.

Online congress discussing state of the art computational chemistry

FACCTs is bringing the ORCA software to industry - promoting the next Quantum leaps in the Pharma, Materials and Chemical Industries.

The catalytic efficacy of a novel mononuclear rhenium(I) complex in CO2 reduction is remarkable, with a turnover number (TONCO) of 1517 in 3 h, significantly outperforming previous Re(I) catalysts. Th...

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(2S,3S)-4-Fluorovaline (FVal) is an analogue of valine, where a single CH3 group is substituted by a CH2F group. In the absence of valine, E. coli valyl-tRNA synthetase uses FVal as a substitute, enabling the production of proteins uniformly labeled with FVal. Here, we describe the production and analysis of E. coli peptidyl–prolyl isomerase B where all 16 valine residues have been replaced by FVal synthesized with a 13C-labeled CH2F group. Although the melting temperature is lower by about 11 °C relative to the wild-type protein, the three-dimensional protein structure is almost completely conserved, as shown by X-ray crystallography. The CH2F groups invariably populate staggered rotamers. Most CH2F groups populate two different rotamers. The increased space requirement of fluorine versus hydrogen does not prohibit rotamers that position fluorine next to a backbone carbonyl carbon. 19F NMR spectra show a signal dispersion over 25 ppm. The most high-field shifted 19F resonances correlate with large 3JHF coupling constants, confirming the impact of the γ-gauche effect on the signal dispersion. The present work is the second experimental verification of the effect and extends its validity to fluorovaline. The abundance of valine in proteins and structural conservation with FVal renders this valine analogue attractive for probing proteins by 19F NMR spectroscopy.

We report an incredibly reducing and redox-active Mn–I dianion, [Mn(CO)3(Ph2B(tBuNHC)2)]2– (NHC = N-heterocyclic carbene), furnished via 2e– reduction of the parent 16e– MnI complex with Na0 or K0. Cy...

The unfavorable scaling (N5) of the conventional second-order Møller–Plesset theory (MP2) typically prevents the application of double-hybrid (DH) density functionals to large systems with more tha...