Q-Chem

Read this preprint in which Manisha and Prashant Uday Manohar present their FNO implementation for EOM-CCSDT for IP, DIP, EA, and DEA. Their implementation is available in Q-Chem 6.3! arxiv.org/pdf/2509.141...

Try FNO-CCSDT yourself in Q-Chem: q-chem.com/try/

Coming soon to Q-Chem: Periodic boundary conditions! Read this preprint from researchers at Harvard, who present a new method for modeling electrochemical interactions at solid-liquid interfaces: doi.org/10.48550/arX...

Learn more about PBC in Q-Chem: q-chem.com/webinars/73/

Don't miss the next Q-Chem webinar this Friday! Xinchun Wu will be discussing the exciting work she did at Q-Chem this past summer, including constrained CASSCF for studying nonadiabatic systems and tight-binding calculation features. Register here: zoom.us/webinar/regi...

Congratulations to Q-Chem developers on their recent publication, in which they develop non-orthogonal quasi-degenerate perturbation theory to enable XPS calculations for L-edge and beyond! doi.org/10.1021/acs....

Try the new Q-Chem 6.3 release today: q-chem.com/try/

Text reads: "Q-Chem 6.3.1 is here! Upgrade today to enjoy improved performance and usability, and check out the changelog to learn about the latest features!"

Q-Chem is pleased to introduce our latest release, Q-Chem 6.3.1! For a full list of updates, fixes, and resolved issues, please review the release log here: q-chem.com/support/rele...

If you want to try Q-Chem 6.3.1, you can request a demo license here: q-chem.com/try/

Understanding Electronic Excitations Between Single Determinants with Occupied-Virtual Orbitals for Chemical Valence One approach to calculating electronic excited states treats both ground and excited states as single determinants, either by direct optimization or with the aid of constraints. In this work, we exten...

Congratulations to Q-Chem developers on their recent paper, in which they extend occupied-virtual orbitals for chemical valence (OVOCV) in Q-Chem to study transitions between ground and excited states. doi.org/10.1021/acs....

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Aufbau Suppressed Coupled Cluster As a Post-Linear-Response Method We investigate the ability of Aufbau suppressed coupled cluster theory to act as a post-linear-response correction to widely used linear response methods for electronically excited states. We find that the theory is highly resilient to shortcomings in the underlying linear response method, with final results from less accurate starting points nearly as good as those from the best starting points. This pattern is especially stark in charge transfer states, where the approach converts starting points with multi-eV errors into post-linear-response results with errors on the order of 0.1 eV. These findings highlight the ability of Aufbau suppressed coupled cluster to perform its own orbital relaxations and raise the question of whether initializing it with an orbital relaxed reference is worth the trouble.

Check out this recent paper from researchers at UC Berkeley, who use Q-Chem's EOM-CC, TDDFT, and excited state analysis module to investigate a new correction to linear response methods for excited states. doi.org/10.1021/acs....

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In this paper, Q-Chem developers present a novel EOM-CC-based approach for computing Auger decay rates. Their exciting new implementation was done in Q-Chem! doi.org/10.1039/D5CP...

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

Q-Chem developers use TDDFT-1D in Q-Chem to study the photodynamics of TCNE-HMB, gaining useful insights with exciting implications for the applicability of Marcus theory to photochemistry in non-innocent solvents. doi.org/10.1021/acs....

Try Q-Chem: q-chem.com/try/

Don't forget, you can now run Q-Chem calculations easily on AWS with Q-Cloud! The command line interface makes it quick and easy to set up and launch a cluster in the cloud. Learn more here: q-chem.com/explore/qclo...

In this paper, KS-DFT and TAO-DFT in Q-Chem are used to study vibrational stabilization in cyclacene carbon nanobelts. Static correlation (via TAO-DFT) is found to be essential for an accurate description. doi.org/10.1021/acs....

Learn about TAO-DFT: q-chem.com/explore/dft/...

Ultrafast Transversal CISS Effect Observed in a Chiral Photoswitching Molecule Progress in the fundamental understanding of the chirality-induced spin-selectivity (CISS) effect is hindered by complexity of the systems that have been characterized experimentally. With the goal of...

Researchers use EOM-EA-CCSD in Q-Chem to study the chirality-induced spin-selectivity (CISS) effect in a chiral molecule that can also act as a photoswitch, providing useful fundamental insights into CISS: doi.org/10.1021/acs....

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John Herbert receives the 2024-2025 Diversity Enhancement Faculty Award 2024-2025 Diversity Enhancement Faculty Award This award recognizes a faculty member from within The Ohio State University College of Arts and Sciences whose research, teaching and/or service/outreach...

Congratulations to Q-Chem developer and board member Prof. John Herbert on receiving the 2024-2025 Diversity Enhancement Faculty Award! You can read the official press release here: chemistry.osu.edu/news/john-he...

Instability of the Octahedral Symmetry in Si8O12H8 and Ge8O12H8: A Consequence of the Pseudo-Jahn–Teller Effect - Journal of Inorganic and Organometallic Polymers and Materials The symmetry breaking in octahedral silsesquioxane and its germanium analogues (Si8O12H8 and Ge8O12H8) has been investigated using the M06-2X/6-31++G(3df, 3pd) method and group theory. Both structures...

In this paper, authors use Q-Chem's geometry optimizer and DFT alongside group theory to study symmetry breaking in octahedral silsesquioxane and germanium analogues, which are used in nanohybrid functional materials. doi.org/10.1007/s109...

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Rationalising Exciton Interactions in Aggregates Based on the Transition Density Exciton coupling in organic chromophores is revisited through the lens of the transition density. The presented formalism gives insight into the strength and sign of the coupling based on the relativ...

In this recent paper, authors use Q-Chem's DFT and wavefunction analysis tools to study excitonic coupling in chromophore aggregates. They present a new model for estimating sign and magnitude of excitonic coupling. doi.org/10.1002/chem.202501570

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Don't miss tomorrow's webinar from Mathew Chow! He will discuss NEO-DFT and real-time NEO-TDDFT methods, along with NEO quantum mechanical/molecular mechanical approaches. Register: zoom.us/webinar/regi...

Development of a Spectroscopic Map to Explain the Broad Raman Peak for Alkynes Solvated in Triethylamine The terminal alkyne C≡C stretch has a large Raman scattering cross section in the “silent” region for biomolecules. Experimental work taking advantage of this property provide an impetus for the development of theoretical tools addressing the vibration. In prior work, we have developed a localized normal mode method for computing terminal alkyne vibrational frequencies using a discrete variable representation of the potential energy surface. Using this method and molecular dynamics simulations, we interpret the unusually broad Raman spectrum of alkynes solvated in triethylamine. Energy decomposition analysis is performed on alkyne-triethylamine dimers to determine that charge transfer, electrostatics, and Pauli repulsion have large effects on the frequency. Molecular dynamics simulations of triethylamine-solvated alkynes are performed and uncover that the terminal alkyne hydrogen interacts strongly with the triethylamine nitrogen. Interactions persist for 3–10 ps. Using this data, a spectroscopic map for terminal alkynes is developed and used to compute Raman spectra for alkynes in triethylamine. We find that the broad experimental spectra result from the combination of a population of alkynes associated with the solvent nitrogens and a population not associated with those nitrogens. This work sets the stage for investigations of alkynes in more complex environments like proteins and nanomaterial surfaces.

In this recent paper, researchers at Haverford College use MD alongside Q-Chem's DFT to help explain why the Raman peak for alkynes solvated in triethylamine is so unusually broad. Read the paper here: pubs.acs.org/doi/full/10....

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Join us next week for the 2025 Wormit Award Webinar, to be presented by awardee Mathew Chow! He will discuss NEO-DFT and real-time NEO-TDDFT methods, along with NEO quantum mechanical/molecular mechanical approaches. Register here: zoom.us/webinar/regi...

Text reads: "Lab Exercises Designed to be used in physical chemistry classrooms with our free IQmol server. Webinar & Lecture Recordings Browse our archive of recordings. Workshop Materials Recordings and materials from previous user workshops are available for free on our website."

As the academic year starts back up again, don't forget about Q-Chem teaching and learning resources! We provide a variety of free resources on our website, including labs, webinars, and course materials from previous Q-chem workshops. Check it out here: www.q-chem.com/learn/

WebMO 25 is now available! It has a variety of new, exciting features that make its web-based interface to computational chemistry packages even better—and best of all, it now includes support for our latest release, Q-Chem 6.3!

Run calculations for free on their demo server: webmo.net/demo/

Effects of Conformational Sampling on Computing Redox Properties Using Linear Response Approach Redox processes are an important step in many chemical and biochemical reactions. One simple approach to calculate the free energy change of a redox process is linear response approximation (LRA). However, variability in conformational and energy-gap sampling poses a challenge in balancing computational cost and accuracy. Herein, we calculate the redox properties of the one-electron oxidation processes for small, biologically relevant redox-active molecules (e.g., phenol, phenolate, benzene, indole, lumiflavin) in aqueous solution using two conformational sampling strategies. We sampled the conformations using molecular mechanics (MM) and hybrid quantum mechanics/molecular mechanics (QM/MM) simulations to investigate how these techniques affect redox properties. We also performed QM/MM energy-gap sampling while varying the QM region to investigate its impact on overall redox behavior. We observed free energy of oxidation, and consequently, oxidation potential differs consistently by ∼0.2–0.4 V between QM/MM and MM sampling for the molecules under investigation. Overall, we infer that computationally cheaper MM sampling would be adequate for computing the redox properties of small molecules when corrected by a system-specific correction factor.

In this recent work, researchers compare MM and QM/MM approaches to conformational sampling for the calculation of redox properties. They use Q-Chem for the QM/MM single-point energy calculations.

S. Maity, R. Sarangi, and A. Acharya. J. Phys. Chem. B. 2025.
doi.org/10.1021/acs....

Graph Convolutional Neural Network-Enabled Frontier Molecular Orbital Prediction: A Case Study with Neurotransmitters and Antidepressants With the advancement of artificial intelligence-embedded methodologies, their application to predict fundamental molecular properties has become increasingly prevalent. In this study, a graph convolut...

Researchers use a #neuralnetwork to study how the chemical hardness of neurochemicals relates to their affinities for neuroreceptors, specifically focusing on neurotransmitters and antidepressants. They use Q-Chem for their #DFT calculations. doi.org/10.1021/acs....

Join us on July 31 at 11AM for our Nick Besley Award Webinar! The webinar will be presented by award winner Prof. Justin Talbot; he will be discussing his recent work on developing methods for studying excited state potential energy surfaces. Register: zoom.us/webinar/regi...

Q-Chem was honored to be one of the sponsors of the 2025 MERCURY Conference at UPitt last week! We were excited to hear the multitude of ways that many of these students and professors are using Q-Chem in their ongoing research work. Thanks to those who stopped by!

Revisiting a large and diverse data set for barrier heights and reaction energies: best practices in density functional theory calculations for chemical kinetics Accurate prediction of barrier heights and reaction energies is of paramount importance for reaction kinetics. For computational efficiency, such calculations are typically performed with density func...

"This workflow provides crucial insights into when Kohn-Sham DFT and even gold-standard CCSD(T) may be unreliable, particularly in the presence of strong static correlation."

Read the paper: doi.org/10.1039/D5CP...
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(4/4)

"We propose our orbital stability analysis-based 3-tier classification workflow as a best-practice protocol for DFT calculations in chemical kinetics." (3/4)

"By analyzing spin-symmetry breaking at both the SCF and κ-OOMP2 levels, we classified reactions based on the nature and extent of electron correlation, traced key sources of error, and addressed them to the degree possible." (2/4)

Text reads: "Revisiting a large and diverse data set for barrier heights and reaction energies: best practices in density functional theory calculations for chemical kinetics. Xiao Liu, Kevin A. Spiekermann, Angiras Menon, William H. Green, and Martin Head-Gordon. PCCP. May 2025."

Congratulations to Q-Chem developers and collaborators on their PCCP Hot Paper!

From author Xiao Liu: "In this work, we present a thorough investigation into the unexpectedly large RMSDs for the ωB97X-D3 functional previously reported on the RDB7 dataset (~12,000 reactions)..." (🧵1/4)

This week, we featured papers that used various Q-Chem features, including TD-DFT with SOC, X-ray spectroscopy, CAP-EOM-EA-CCSD, and efficient gradients for localized diabatic state energies and couplings. Want to try these yourself? Request a free trial: q-chem.com/try/

Authors investigate electron scattering in nitrous oxide, using Q-Chem's CAP-EOM-EA-CCSD and ezFCF to explain features of the experimentally-observed experimental two-dimensional electron energy loss (EELS) spectra. doi.org/10.26434/chemrxiv-2025-m5dnl