Q-Chem

Computation of Partial Auger Decay Widths from Complex-Valued Equation-of-Motion Coupled-Cluster Energies We discuss the computation of partial Auger decay widths with equation-of-motion ionization-potential coupled-cluster (EOMIP-CCSD) theory in the framework of non-Hermitian quantum mechanics (NHQM). In NHQM, the decaying character of metastable states is described with complex energies and the total decay width is obtained directly from the total energy. In contrast, the computation of partial decay widths, i.e., the contributions of different decay channels to the total width, requires further analysis. However, partial widths are important for Auger spectroscopy as they determine the probability with which different final states are formed and hence the shape of the Auger spectrum. Recently, we introduced Auger channel projectors (ACPs), which selectively remove decay channels from the EOMIP-CCSD excitation manifold. This method requires a separate EOMIP-CCSD calculation for each decay channel. Here, we suggest an alternative: We solve the EOMIP-CCSD equations for the core-ionized state in the full excitation manifold and decompose the imaginary part of the resulting energy. In this way, we obtain all partial decay widths at once. We compute Auger spectra for K-edge-ionized states of methane, ethane, and hydrogen sulfide, and a Coster–Kronig spectrum for L1-edge-ionized hydrogen sulfide. The results obtained with our new approach differ only negligibly from ACP results. We also present the first Auger spectra for the cyanide anion, including vibrational broadening, and discuss the differences between the spectra of the carbon core hole and the nitrogen core hole.

Check out the latest paper from Q-Chem developers at KU Leuven, in which they present a new method for computing partial Auger decay widths faster and more robustly! doi.org/10.1021/acs....

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Congratulations to researchers at CSU Fullerton on their recent paper! They develop descriptors for photoacidity and photobasicity; they use several Q-Chem capabilities (including DFT and libwfa) in their work. doi.org/10.1021/acs....

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Check out this recent preprint! Authors present benchmarks of several SF-TDDFT variants and assess the efficacy of each for modeling strongly correlated systems. They use Q-Chem's SF and SA-SF. doi.org/10.26434/che... #compchem #DFT

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In this recent paper, authors introduce a new geometrical descriptor for covalency. They use Q-Chem's EDA, a well-established descriptor for covalency, as a point of comparison for their new metric. doi.org/10.1039/D5DT...

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In this recent work, authors study the interplay of several factors in the stability of cyclacenes, using Q-Chem's TAO-DFT to accurately capture the strong correlation. doi.org/10.1002/jcc....

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In this recent preprint, Q-Chem developers use Q-Chem as the back-end driver for open-source code Fragme∩t to do large-scale fragment-based predictions of protein-ligand interactions! Read more here: chemrxiv.org/doi/full/10....

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Exploring the Isomer Landscape, Fragment Additivity, and Vibrational Signatures of the Z-Alanine Protected Amino Acid Derivative The N-benzyloxycarbonyl-l-alanine molecule is a derivative of the l-α-alanine amino acid with a benzyl carbamate protecting group at the N-terminus, more commonly denoted Cbz-Ala or Z-Ala. In this computational investigation, we sought to determine the available isomers of Z-Ala and their distinguishing spectroscopic signatures via quantum-chemistry methods. Sixty-five total isomers were obtained, and coupled-cluster- and perturbation-theory-based relative energies were computed. The two nearly degenerate, lowest-energy isomers were found to differ in their configuration than the lowest-energy form of isolated alanine, suggesting that the protecting group changes the dominant form of Ala. Through comparisons to exhaustive sampling of Ala and benzyl formate isomers, nearly all of the Z-Ala structures could be ascribed to fragment-paired structural motifs, with a few outliers exhibiting new intramolecular interactions between the constituent fragments. Based on this observation, an assessment of the additivity of the two fragments’ relative energies was performed for Z-Ala energies. Many of the isomers’ energies were reasonably described by such considerations, although backbone strain and hydrogen-bonding interactions altered this energy landscape and led to nonadditive effects for several of the isomers. Comparison to experimental REMPI-based UV/IR ion-dip vibrational spectra in the 90–1822 cm–1 region indicated that two isomers are dominantly present at the experimental conditions, although signatures of other isomers from the ensemble were also observed. Clear assignments of structural motifs were possible through this experimental comparison. Computed coupled-cluster benchmarks allowed for methodology assessments in this study. The modified opposite-spin MP2 method (MOS-RI-MP2) was found to be particularly accurate, relative to these benchmarks, after minor adjustment of the range-separation parameter. Density functional theory (DFT) methods were found to be variable in their accuracy for both energies and spectra, although a few key functionals performed particularly well for this system in the low-frequency region of the vibrational spectrum. These methodology constraints provided recommendations for similar systems and subsequent anharmonic analyses.

In this new paper, authors determine over sixty isomers of Z-Ala and study their spectroscopic signatures. They use Q-Chem for ab initio simulations with 144 DFT functionals, CCSD, and PT (RI-MP2, MOS-MP2, and MP2.5). doi.org/10.1021/acs....

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Transition State Model for the Manganese-Based Chemical Hydrogen Battery Transition state modeling is a powerful tool for unraveling the mechanistic intricacies of chemical reactions. It plays a pivotal role in the design of innovative catalytic systems, facilitating progress in the field of catalysis. A carbon-neutral chemical hydrogen battery is the most relevant approach for the storage and transportation of hydrogen fuel. Herein, with the aid of transition state models, we decipher the mode of activity of the pincer-ligated manganese complex that enables the reversible hydrogenation and dehydrogenation process for the efficient H2 storage and release. We identified the critical contributions from the basic amino acids, specifically lysine and its potassium salt, as well as the influence of solvent, counterions, and water, in governing the reversibility. In addition, we have probed into the role of noncovalent interactions during the capture and release of CO2 by potassium lysinate, thereby enabling the realization of a carbon-neutral chemical hydrogen battery system.

In this recent paper, researchers study carbon-neutral storage and release of H2, using Q-Chem's second-generation EDA for an in-depth exploration of the interaction energies of transition states. doi.org/10.1021/acsc...

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The videos from the Q-Chem workshops last week at the Virtual Winter School on #CompChem are posted! If you missed us, you can watch the talks and work through the exercises here: winterschool.cc/program/day-...

Don't forget, Q-Chem has two VWSCC workshops happening over the next 24 hours: One at 9am CET, and another at 10pm CET! Join whichever fits your timezone best. Register here: winterschool.cc

2026 Nick Besley and Michael Wormit Award nominations are due this week! If you know someone who develops in Q-Chem or works with computational spectroscopy methods, please consider nominating them.

Wormit Award: q-chem.com/about/wormit/
Besley Award: q-chem.com/about/besley/

Don't forget about the 2026 Virtual Winter School in Computational Chemistry (VWSCC) meeting, happening next week! This is a great (free!) opportunity to learn and network, including talks and hands-on workshops! Learn more and register here: winterschool.cc #compchem

Don't forget about the upcoming Q-Chem webinar from Avik Ojha; he will discuss his recent work implementing X-ray spectroscopy features in Q-Chem (including XCIS-CVS, which is now available now in Q-Chem 6.4)! Register here: zoom.us/webinar/regi...

Don't miss next week's webinar from Q-Chem developer Avik Ojha (OSU), who will be talking about his recent CVS-XCIS implementation in Q-Chem for X-ray spectroscopy modeling. Read the abstract and register here: zoom.us/webinar/regi...

Q-Chem is thrilled to be one of the sponsors for the 2026 Virtual Winter School on Computational Chemistry! This year's schedule includes many exciting lectures and hands-on workshops, including a Q-Chem workshop. Learn more and register: winterschool.cc #compchem

Happy New Year! As we enter 2026, we want to celebrate the accomplishments of the Q-Chem community over the past year. Check out our 2025 Year In Review publications list: q-chem.com/news/2025-qc...

Thanks to all of our users and developers for making Q-Chem possible! ✨💫

Webinar 84: Modern Quantum Chemistry in Q-Chem 6.4 YouTube video by QChemSoftware

Did you miss the recent Q-Chem 6.4 launch event? Not to worry! Watch this webinar recording from John Herbert to learn about our latest release, including a variety of exciting new features: youtu.be/PXMXKPXd8Ok

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Q-Chem 6.4 includes Robust SCF: A simple black-box approach for improved convergence! It automatically detects and corrects common SCF convergence issues, including plateauing, oscillation, and unstable solutions. manual.q-chem.com/6.4/sub_scf_...

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In Q-Chem 6.4: Stochastic RI-CC2 analytical gradients and derivative coupling! Obtain accurate CC2 gradients faster, with O(N4) scaling with basis set size. Check out the recent preprint from developers:
doi.org/10.48550/arX...

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Q-Chem 6.4 includes new B97-type functionals for TAO-DFT! Read this paper from developers Shaozhi Li and Jeng-Da Chai, where they develop methods that perform well for both single- and multi-reference systems. doi.org/10.1021/acs....

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New in Q-Chem 6.4: Iterative CC-in-DFT embedding! This new approach, developed by Anthuan Ferino Pérez and Thomas Jagau, provides high accuracy for relevant properties at lower cost. Read their paper to learn more: doi.org/10.1021/acs....

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New in Q-Chem 6.4: Faster coupled cluster calculations! Our new two-step Cholesky decomposition for CC and EOM-CC energy and gradient (developed by Tingting Zhao and Anna Krylov) provides speedup. Learn more about features in our new release: q-chem.com/explore/qc64/

Q-Chem 6.4 is here! Upgrade for new spectroscopy features (such as CVS-XCIS our new-and-improved ΔSCF driver), iterative CC-in-DFT embedding, faster CC calculations, MR-SF-DFT, stochastic RI-CC2, NEO methods, and more: q-chem.com/explore/qc64/

New in Q-Chem 6.4: XCIS-CVS! In a new paper, researchers use XCIS-CVS to accurately calculate core-level spectra for open-shell molecules, including transition metal complexes. doi.org/10.1021/acs....

CVS for ROCIS, CIS, and QROCIS is available in Q-Chem 6.4, coming next week!

New in Q-Chem 6.4: Improved ΔSCF! The input for ΔSCF is now one simple, easy-to-use section, making it easier to run than ever. The new ΔSCF driver (developed by Juanes Arias-Martinez) includes several other useful functionalities.

Q-Chem 6.4 is coming next week. Stay tuned!

Check out this new paper: Authors use Q-Chem's EA-TDDFT and ALMO-EDA-PCM to uncover evidence pointing to the presence of interanionic hydrogen bonding (IAHB) in concentrated phosphoric acid solutions. pubs.acs.org/doi/10.1021/...

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Coupled-Cluster in Density Functional Theory Embedding Applied to Static Polarizabilities in Aqueous Environments We present a study of static polarizabilities of organic molecules in aqueous environments using projection-based coupled-cluster in density functional theory quantum embedding. We propose two methods...

Check out this recent paper in JCTC, in which authors pioneer the use of iterative CC-in-DFT embedding in Q-Chem to study static polarizabilities for organic molecules in aqueous environments. doi.org/10.1021/acs....

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Check out this recent preprint from Q-Chem developers at KU Leuven, who use EA-EOM-RICC2 in Q-Chem to study the reduction of ubiquinone (CoQ), a key step in cellular respiration. doi.org/10.26434/che...

Interested in becoming a Q-Chem developer? Learn more here: www.q-chem.com/about/team/d...

Don't miss tomorrow's webinar from Manisha on coupled cluster triples! If you can't make it at the scheduled time, still be sure to register—the webinar recording will be made available afterwards. zoom.us/webinar/regi...

Join us on 11/19 at 9PM PST for a webinar from Manisha, one of our 2025 Summer at Q-Chem interns! She will discuss her recent work with coupled cluster, including her recent Q-Chem implementations of CCSDt and several EOM-CCSDT variants. Register here: zoom.us/webinar/regi...