Thomas Froitzheim

g-xTB: A General-Purpose Extended Tight-Binding Electronic Structure Method For the Elements H to Lr (Z=1–103) We present g-xTB, a next-generation semi-empirical electronic structure method derived from tight-binding (TB) approximations to Kohn–Sham density functional theory (KS-DFT). Designed to bridge the gap between semi-empirical quantum mechanical (SQM) approaches and DFT in terms of accuracy, robustness, and general applicability, g-xTB targets the performance of the ωB97M-V range-separated hybrid density functional with large basis sets while maintaining TB speed. Key innovations include an atom-in-molecule adaptive atomic orbital basis, a refined Hamiltonian incorporating range-separated approximate Fock exchange, up to fourth-order charge-fluctuation terms with a novel first-order electronic contribution, and atomic correction potentials (ACPs), as well as a charge-dependent semi-classical repulsion function. Parameterized on extended and extremely diverse molecular training sets – including “mindless molecules” – g-xTB achieves excellent accuracy across a broad chemical space, including the actinide elements. Benchmarking against around 32k relative energies across thermochemistry, conformational energetics, non-covalent interactions, and reaction barriers shows that g-xTB consistently outperforms GFN2-xTB, often reducing mean absolute errors by half. Notably, it achieves a WTMAD-2 of 9.3 kcal mol−1 on the full GMTKN55 benchmark, comparable to low-cost DFT methods. It also shows substantial improvements for transition-metal complexes, relative spin state energies, and orbital energy gaps – areas where many SQM and even DFT methods often struggle. In summary, g-xTB offers DFT-like accuracy with minimal computational overhead compared to its predecessor, GFN2-xTB, making it a robust, minimally empirical, transferable, and efficient alternative to machine learning interatomic potentials for a wide range of molecular simulations. It is proposed as a general replacement for the GFNn-xTB family and, in many practical cases, a viable substitute for low- and mid-level DFT methods.

#RobSelects preprint 1 of the week #ChemRxiv: Reaching density functional approxmation accuracy at the cost of extended tight-binding quantum chemistry. #compchem https://doi.org/10.26434/chemrxiv-2025-bjxvt

You can now use g-xTB @grimmelab.bsky.social with ORCA via the ExtOpt feature! Check out our new tutorial and learn how to use it in GOAT, NEB-TS and more.

www.faccts.de/docs/orca/6....

#ORCAqc #FACCTs #gxTB #CompChem #QuantumChem

I'm at the WATOC #CompChem conference in Oslo. Machine learning is everywhere, but the hottest news so far is the new g-xTB method by @grimmelab.bsky.social . The results presented today are truly impressive. I'm already running first calculations on our biomolecular systems...

Some exciting talks from Q-Chem developers are happening this morning at #WATOC2025 (06/26):

Thomas Froitzheim (B1, 8:30AM)
∆g-xTB: Excited states with state-specific extended Tight-Binding

Lin Lin (A1, 8:30AM)
Finite-size error in quantum chemistry methods for periodic systems

Two of them are at #WATOC2025 this week and ready to share all the details about the method you’ve been waiting for:
📍 @thfroitzheim.bsky.social — Thursday, Session B1, 9:20 AM
📍 S. Grimme — Thursday, Session A2, 10:20 AM

Don’t miss it!

g-xTB: A General-Purpose Extended Tight-Binding Electronic Structure Method For the Elements H to Lr (Z=1–103) We present g-xTB, a next-generation semi-empirical electronic structure method derived from tight-binding (TB) approximations to Kohn–Sham density functional theory (KS-DFT). Designed to bridge the ga...

After almost 3 years of development with @grimmelab.bsky.social, a first preliminary version of our next-generation general extended Tight-Binding (g-xTB) is now on ChemRxiv!
Catch the details at #WATOC: my talk (Thu Session B1) and Stefan’s talk (Thu Session A2).
#compchem

doi.org/10.26434/che...

GitHub - thfroitzheim/multicharge at eeq-bc Electronegativity equilibration model for atomic partial charges - GitHub - thfroitzheim/multicharge at eeq-bc

Adapting some of these ideas with a broad parametrization really does the trick for EEQBC.

Currently, you still need my branch of multicharge (github.com/thfroitzheim...) but it will be in the next release.
To test it just use: "multicharge struc.xyz --model eeqbc"

The Bond Capacity Electronegativity Equilibration Charge Model (EEQBC) for the Elements Z=1–103 The accurate and efficient assignment of atomic partial charges is crucial for many applications in theoretical and computational chemistry, including polarizable force fields, dispersion corrections, and charge-dependent basis sets. Classical charge models struggle to distinguish between neutral and zwitterionic fragments because, unlike quantum mechanical methods, there are no discrete electronic states. This limitation can lead to either reduced or additional artificial charge transfer (CT) at different interfragment distances. To address this issue, we propose a new version of a bond capacity electronegativity equilibration (EEQBC) model, which limits artificial CT between distant fragments in the simple EEQ framework. EEQBC offers excellent agreement with DFT-based reference charges for elements up to lawrencium (Z = 103) with mean absolute errors as low as 0.02 and 0.07 e− for random PubChem molecules and "mindless" molecules (MLMs), respectively. Thanks to its computational efficiency for both atomic charges and their analytical nuclear gradients, EEQBC is highly suitable as an initial charge guess for next-generation tight-binding methods. For seamless accessibility, EEQBC is implemented in the freely available multicharge program at: github.com/thfroitzheim/multicharge/tree/eeq-bc.

#RobSelects preprint of the week #ChemRxiv: Efficient and accurate model for atomic partial charges combining electronegativity equilibration with the bond-capacity model. #compchem https://doi.org/10.26434/chemrxiv-2025-1nxwg

The Bond Capacity Electronegativity Equilibration Charge Model (EEQBC) for the Elements Z=1–103 The accurate and efficient assignment of atomic partial charges is crucial for many applications in theoretical and computational chemistry, including polarizable force fields, dispersion corrections, a...

Check out our new EEQBC model!

It delivers accurate and robust atomic charges for all elements up to Z=103. By incorporating bond capacitors, we eliminate most artificial CT while preserving the simplicity and efficiency of classical charge equilibration:

doi.org/10.26434/che...

#compchem

Advanced Charge Extended Hückel (CEH) Model and a Consistent Adaptive Minimal Basis Set for the Elements Z = 1–103 The Charge Extended Hückel (CEH) model, initially introduced for adaptive atomic orbital (AO) basis set construction (J. Chem. Phys. 2023, 159, 164108), has been significantly revised to enhance accur...

Important upgrade for the CEH charge model 📈
We’ve improved accuracy and robustness, and extended it for the actinides with f electrons in the valence space to cover elements all the way up to Z=103, together with the atom-in-molecule adaptive q-vSZP basis set! ⚛️ pubs.acs.org/doi/10.1021/...