New Features in Q-Chem 6.3
Q-Chem 6.3 is here! Upgrade today and enjoy improved performance and usability, as well as new tools for studying chemistry and spectroscopy. With these new features, you can deploy large-scale calculations and workflows, get more accurate results faster, and extend the scope of your research to include systems and research questions that were not previously accessible.
The new features in our latest version include new analysis tools, new methods for open-shell species and high-accuracy calculations, and performance enhancements. Check out our list of highlighted features below, with links to associated research publications from the developers. Request a free demo to try these features yourself!
- DFT performance enhancements: The performance of medium to large DFT energy and force calculations has been substantially improved within the already very fast density fitting approximation. Example timings for the cysteine 11-mer at the B3LYP/def2-TZVP level of theory (2485 basis functions) show ~20% speedup relative to 6.2.2 for RI-J and occ-RI-K.
- Robust SCF: Q-Chem's sophisticated new multi-stage "Robust SCF" procedure provides significantly more robust SCF convergence, including automatic detection and correction of incipient SCF divergence and algorithm switching in cases where DIIS fails. This black-box approach will be valuable in big-data applications and will assist with difficult-to-converge cases.
- MPI Parallelization for Finite-Difference and Many-Body Expansion Calculations
- Novel tools for spectroscopy:
- Automated Coulomb wave calculations of Auger decay rates within Feshbach-Fano framework
Saikat Roi and Wojciech Skomorowski - Auger Channel Projection EOMIP-CCSD with frozen core and open shell references
Robin Moorby, Florian Matz, Thomas-C. Jagau - EOM-(EE/SF)-CCSD dynamic polarizability for imaginary frequencies
Kaushik Nanda
- Automated Coulomb wave calculations of Auger decay rates within Feshbach-Fano framework
- New tools for open-shell species and resonances:
- SOC using EOM-DEA and EOM-DIP wave functions
Tingting Zhao, Sai Kotaru, Sahil Gulania, Pavel Pokhilko, Anna Krylov - EOM-DIP/DEA-CCSD gradients
Tingting Zhao, Anna Krylov - Complex-valued RI-EOM-CCSD
Simen Camps, Cansu Utku, Thomas Jagau
- SOC using EOM-DEA and EOM-DIP wave functions
- Advances in many-body methods for better accuracy:
- Implementation of EOM-CCSDT for high accuracy for EE, SF, IP, EA, DIP and DEA
Manisha and Prashant Uday Manohar - CC2 with size-consistent Brillouin-Wigner Partitioning
Linus Dittmer, Nikolay V. Tkachenko, Martin Head-Gordon
- Implementation of EOM-CCSDT for high accuracy for EE, SF, IP, EA, DIP and DEA
- Novel analysis tools:
- Broken bond orbitals (BBOs): Provides a useful EDA framework to study the key mechanisms at play during bond formation.
Alistair J. Sterling, D. S. Levine, A. Aldossary, M. Head-Gordon - Charge-transfer metrics for TDDFT: Q-Chem’s libwfa tools measure electron–hole separation and exciton size using proper expectation values, whereas popular measures of CT character implemented in other codes do not respect orbital invariance and sometimes afford unphysical predictions.
John Herbert - ALMO(MSDFT) diabatic coupling calculation involving ∆SCF excited states
Yuezhi Mao
- Broken bond orbitals (BBOs): Provides a useful EDA framework to study the key mechanisms at play during bond formation.
- Tools for studying chemistry in standard and unusual regimes:
- New mechanochemical pressure model using PV term energy correction
Felix Zeller - New constraints for geometry optimizations and PES scans: Constraints now include torsional and flat-bottom potential restraints for geometry optimization, as well as bond stretch, r12pr34, angle, 1 to midpoint of 2 atoms, 1 to COM, and dihedral restraints for PES.
Chance W. Lander, Yihan Shao
- New mechanochemical pressure model using PV term energy correction
- Tools for including effects of homogeneous and heterogeneous environment:
- Heterogeneous PCM: DFT calculations on cluster models of proteins are a popular way to explore enzymatic mechanisms, but gas-phase boundary conditions are unrealistic. The “HetPCM” model allows parts of the “QM cluster” protein models to be solvent-exposed (dielectric constraint ε = 78) while other parts are buried in hydrophobic regions (ε ≈ 4).
John Herbert - Semi-numerical frequency support for the SMD model: DFT frequency calculations using the SMD solvation model can now be performed at the cost of analytic (rather than finite-difference) frequencies, enabling calculations on medium and large systems.
John Herbert - Density matrix-based and energy-based generalized many-body expansion (GMBE): Density-matrix-based fragmentation schemes can reduce the cost of SCF calculations by an order of magnitude without loss of accuracy in appropriate systems. Unlike some fragmentation methods that require small basis sets, GMBE-DM can be used with high-quality basis sets.
Jake A. Tan, Francisco Ballesteros, Ka Un Lao
- Heterogeneous PCM: DFT calculations on cluster models of proteins are a popular way to explore enzymatic mechanisms, but gas-phase boundary conditions are unrealistic. The “HetPCM” model allows parts of the “QM cluster” protein models to be solvent-exposed (dielectric constraint ε = 78) while other parts are buried in hydrophobic regions (ε ≈ 4).
- Advances in methods for incorporating quantum nuclear effects (NEO suite):
- NEO PCM analytic Hessian for solution phase frequency and normal mode analysis
Mathew Chow, Sharon Hammes-Schiffer - Support for exchange-correlation functionals with additional dispersion correction baked-in (i.e., wB97X-D, wB97X-D3, B3LYP-D3(BJ), etc.) for NEO methods
Mathew Chow, Sharon Hammes-Schiffer - Improved performance by adding simultaneous GDM optimization, improved initial guess (nuclear SCF), and an extension of simultaneous DIIS and GDM optimization to treat an arbitrary number of quantum protons
Mathew Chow, Sharon Hammes-Schiffer
- NEO PCM analytic Hessian for solution phase frequency and normal mode analysis
For a full list of new features and bugfixes, please review the official Q-Chem 6.3 release log here.