Q-Chem

Software for fast and accurate simulations of molecular systems, including electronic and molecular structure, reactivities, properties, and spectra.

Q-Chem, Inc., established in 1993, is a research and development of computational software company. Q-Chem brings commercial, academic and government scientists worldwide in pharmaceuticals, materials science, biochemistry and other fields a comprehensive ab initio quantum chemistry program to solve computational problems faster, more accurately and less expensively than they could otherwise. Its

capabilities range from the highest performance DFT/HF calculations to high level post-HF correlation methods. Q-Chem tackles a wide range of problems in commercial, academic and government laboratories. Q-Chem also provides users with the highest level of technical support possible.

06/02/2026

Upcoming in the Q-Chem 7 release: CAP-DFT! This new approach provides a great way to model metastable molecular anions. Check out this recent paper from the developers: https://pubs.acs.org/doi/10.1021/acs.jpclett.5c04034

From Charlotte Titeca, one of the authors: "We report an implementation of CAP-DFT and complex-variable density functional approximations up to the generalized gradient approximation and derived hybrid functionals, which enables fast and accurate evaluation of the energies and lifetimes of metastable molecular anions. This new method is applied to various molecular systems, including the metastable anions of molecular nitrogen, formaldehyde, formic acid, ethene, and pyrene. Hybrid functionals deliver results that are competitive with equation-of-motion coupled-cluster theory."

Pre-order Q-Chem 7 here: https://www.q-chem.com/purchase/

05/27/2026

Correlated and post-HF methods are essential to any toolkit, providing accurate, reliable results for complex molecular systems. Q-Chem offers state-of-the-art tools for handling electron correlation, such as Møller-Plesset perturbation theory and coupled-cluster theory. It also offers methods for multireference systems, like CASSCF and selected CI.

The Q-Chem 6 generation has introduced and improved several new post-HF methods (including EOM-CCSDT, BW-s2, TDDFT/TDA-SOC, and MRSF-TDDFT), and there are several new features to look forward to in Q-Chem 7.

Stay tuned this week and next as we highlight recent and upcoming work from our developers!

05/25/2026

Homochirality is key in biological systems—for example, DNA is a right-handed helix—but questions about why life is homochiral, and why a specific handedness is favored, are still hotly debated.

In this recent paper, authors leverage quantum chemistry calculations alongside direct experimental measurements to probe the origins of homochirality in biological systems. Their results indicate that electron spin may be the key: Chirality can affect the efficiencies of spin-related processes, providing an advantage for one handedness over the other.

The main thesis of the paper was supported by EOM-EA-CCSD calculations of chiral molecules and all-electron calculations of Breit-Pauli SOC, enabled by Q-Chem.

You can read the paper here:https://iopenshell.usc.edu/pubs/pdf/sciadv-12-aec9325.pdf
This work was also recently highlighted in Phys.org: https://phys.org/news/2026-04-life-electron.html

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

05/22/2026

New in Q-Chem 7: Excited-state analysis based on Earth Mover's Distance (EMD)! This provides a new quantitative metric for characterizing the extent of charge-transfer in excitations.

This new μEMD metric is useful for a wide range of excited state types, is easily extendable to other excited-state methods like OO-DFT, and can be used as a diagnostic tool to flag cases where pure XC functionals produce inaccurate excitation energies. Learn more by reading the paper from the developers in JCTC: https://doi.org/10.1021/acs.jctc.3c00894

Pre-order Q-Chem 7 today: http://q-chem.com/purchase/

05/20/2026

Δ-ALMO(MSDFT2), first introduced in Q-Chem 6.3, is an inexpensive way to model excited state diabatization. It combines the popular ΔSCF approach with ALMO to generate diabatic states, then uses MSDFT2 to obtain their couplings with charge-transfer states.

Their technique provides accurate results for problems involving excited state electron and hole transfer for charged and uncharged systems. Read the paper from developers where they test Δ-ALMO(MSDFT2) on systems ranging from singlet fission to systems involved in DNA repair: https://doi.org/10.1063/5.0035593

This method is now available in Q-Chem! Try today: http://q-chem.com/try/

05/18/2026

New in Q-Chem 7: Excited-state analysis for MRSF-TDDFT! This includes natural orbitals (NOs), natural transition orbitals (NTOs), natural difference orbitals (NDOs), and related descriptors through the libwfa framework.

MRSF-TDDFT is a new method for handling strongly correlated systems that avoids the spin contamination issues common in traditional SF-TDDFT. MRSF-TDDFT energies were added to Q-Chem last year (version 6.4), and we are excited to have this extension to properties included in our upcoming release.

Read the preprint from the Q-Chem developers about their new implementation: doi.org/10.26434/chemrxiv.15002538/v2

05/16/2026

A practical application of Q-Chem's wave-function analysis toolkit: Developers used spin-orbit natural transition orbital analysis for TDDFT and SF-TDDFT (added in Q-Chem 6.1) to assess the character of different states, allowing them to properly compare their spin-orbit coupling results. https://doi.org/10.1063/5.0130868

05/15/2026

In this publication, Q-Chem developers present new charge-transfer metrics for TDDFT; their new approach allows researchers to identify orbitals that are most likely to participate in charge-transfer-to-solvent (CTTS) excitations, which has useful applicability for systems like solution-phase chromophores. https://doi.org/10.1021/acs.jctc.1c00412

Their natural charge-transfer analysis technique was introduced in last year's Q-Chem 6.3 release! You can try it with a free Q-Chem trial: http://q-chem.com/try/

05/11/2026

Q-Chem provides an extended wave-function analysis toolkit (libwfa) that enables visualization of excited states, automatic assignment of properties, and deeper insight into the underlying physics.

The Q-Chem 6 generation has included several additions to our established toolkit, including things like charge-transfer metrics for TDDFT; Δ-ALMO(MSDFT2); and spin-orbit NTO analysis for TDDFT and SF-TDDFT.

Follow along this week as we highlight some of these developments!

05/08/2026

The chemical bond is fundamental to chemistry, but, as any chemist knows, understanding the origin of chemical bonding can be tricky.

The broken bond orbital (BBO) approach, introduced in Q-Chem 6.3, uses an EDA framework to assess the key mechanisms at play during bond formation. This provides a useful computational tool that helps researchers probe the nature of chemical bonds and understand what physically drives them.

Watch this recent Q-Chem webinar to learn more: https://www.q-chem.com/webinars/78/
Read the BBO paper here: https://doi.org/10.1021/jacs.3c10633

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