Happy New Year: Q-Chem Year In Review (2025)

Happy New Year from Q-Chem! As we welcome 2026, we wanted to take a moment to celebrate what Q-Chem users and developers have accomplished over the past year, including: Over 1,000 publications and preprints citing Q-Chem; 2,129 commits to the Q-Chem code base (172 merges to trunk); and more than 50 new cutting-edge features contributed to Q-Chem by developers!

We have compiled a list below highlighting some developer publications and preprints from 2025. Many of the new methods pioneered in these papers are now available in Q-Chem 6.4!

Please note that the list below is not comprehensive. If you would like to see a specific journal article or preprint highlighted on this list, please submit the publication using the form here. Thanks to all of our users and developers for making Q-Chem possible, and best wishes for a productive 2026!

• Equation-of-motion Coupled-cluster singles, doubles and(full) triples for doubly ionized and two-electron-attached states: A Computational implementation
  Manisha, Prashant Uday Manohar, and Anna I Krylov. Preprint. January 2025.
  Features: EOM-CCSDT
   
• Repartitioning the Hamiltonian in many-body second-order Brillouin–Wigner perturbation theory: Uncovering new size-consistent models
  Linus Bjarne Dittmer and Martin Head-Gordon. J. Chem. Phys. February 2025.
  Features: CC2 with size-consistent Brillouin-Wigner Partitioning
   
• Using Conformational Sampling to Model Spectral and Structural Changes of Molecules at Elevated Pressures
  Felix Zeller, Philipp Pracht, Tim Neudecker. J. Phys. Chem. A. February 2025.
  Features: New mechanochemical pressure model using PV term energy correction
   
• Testing a Heterogeneous Polarizable Continuum Model against Exact Poisson Boundary Conditions
  Paige E. Bowling, Montgomery Gray, Suranjan K. Paul, and John M. Herbert. JCTC. February 2025.
  Features: HetPCM
   
• Complex-Variable Equation-of-Motion Coupled-Cluster Singles and Doubles Theory with the Resolution-of-the-Identity Approximation
  Simen Camps, Cansu Utku, Joel Creutzberg, and Thomas-C. Jagau. J. Phys. Chem. A. May 2025.
  Features: Complex-valued RI-EOM-CCSD
   
• Extending Orbital-Optimized Density Functional Theory to L-Edge XPS and Beyond: Spin–Orbit Coupling via Nonorthogonal Quasi-Degenerate Perturbation Theory
  Richard Kang, Leonardo A. Cunha, Diptarka Hait, and Martin Head-Gordon. JCTC. August 2025.
  Features: Non-orthogonal quasi-degenerate perturbation theory to enable XPS calculations for L-edge and beyond
   
• Incorporating the effect of spin–orbit interaction in Auger decay spectra: Theory and examples
  Nayanthara K. Jayadev, Wojciech Skomorowski, and Anna I. Krylov. J. Chem. Phys. September 2025.
  Features: Automated Coulomb wave calculations of Auger decay rates within Feshbach-Fano framework
   
• Optimization of B97-Type Density Functional Approximation, Global Hybrid, and Range-Separated Hybrid Energy Functionals with the D4 Dispersion Corrections in TAO-DFT
  Shaozhi Li and Jeng-Da Chai. JCTC. September 2025.
  Features: B97-type functional support for TAO-DFT
   
• Nuclear-electronic orbital second-order coupled cluster for excited states
  Jonathan H. Fetherolf, Fabijan Pavošević, and Sharon Hammes-Schiffer. Preprint. September 2025.
  Features: NEO-CC2
   
• Stochastic resolution of identity to CC2 for large systems: Excited-state gradients and derivative couplings
  Chongxiao Zhao, Chenyang Li, and Wenjie Dou. Preprint. September 2025.
  Features: Stochastic RI-CC2 energy, gradients, and derivative couplings
   
• Coupled-Cluster in Density Functional Theory Embedding Applied to Static Polarizabilities in Aqueous Environments
  Anthuan Ferino-Pérez and Thomas-C. Jagau. JCTC. September 2025.
  Features: Iterative CC-in-DFT embedding
   
• Frozen Natural Orbitals based Equation-of-motion coupled-cluster singles, doubles and triples for Ionized, Double-Ionized, Electron Attached and Two-Electron Attached states
  Manisha and Prashant Uday Manohar. Preprint. September 2025.
  Features: IP, DIP, EA and DEA variants of FNO-EOM-CCSDT
   
• Gaussian-Based Periodic Grand Canonical Density Functional Theory with Implicit Solvation for Computational Electrochemistry
  Anton Z. Ni, Adam Rettig, and Joonho Lee. JCTC. October 2025.
  Features: QCPBC (for periodic boundary conditions, coming in Q-Chem 7!)
   
• Regularized Perturbation Theory for Ab Initio Solids
  Meng-Fu Chen, Jinghong Zhang, Hieu Q. Dinh, Adam Rettig, and Joonho Lee. J. Phys. Chem. Lett. October 2025.
  Features: QCPBC (for periodic boundary conditions, coming in Q-Chem 7!)
   
• Extended Configuration-Interaction Singles Method with Core/Valence Separation (XCIS-CVS): Core-Level Spectra of Open-Shell Molecules
  Avik Kumar Ojha and John M. Herbert. JCTC. November 2025.
  Features: Core-valence separation (CVS) scheme for ROCIS, XCIS, and QROCIS
   
• Locating Ab Initio Transition States via Geodesic Construction on Machine-Learned Potential Energy Surfaces
  Diptarka Hait, Jan D. Estrada Pabón, Martin Stöhr, and Todd J. Martínez. JCTC. November 2025.
  Features: P-RFO transition state optimization and DFT
   
• Structural Evidence of Interanionic Hydrogen Bonding in Phosphoric Acid Solutions
  Pyeongeun Kim, Richard Kang, Kevin Carter-Fenk, Kevin R. Wilson, Martin Head-Gordon, and Musahid Ahmed. JACS. November 2025.
  Features: EA-TDDFT and ALMO-EDA-PCM