New Optimized Parameters of Extended Tight‐Binding Method Ln‐xTB (Ln = La‐Lu) to Explore Lanthanide Molecular Chemistry

In this work, we newly optimized the parameters of the extended tight‐binding method Ln‐xTB for the entire lanthanide (Ln) series (La to Lu) by using a genetic algorithm (GA) and incorporating a relativistic Hamiltonian, enabling accurate exploration of lanthanide molecular chemistry in complex environments. To validate the accuracy and reliability of Ln‐xTB, we conducted comprehensive benchmarks on different classes of lanthanide‐containing molecules (including halides, aqua complexes, and ligand‐coordinated complexes) and compared results with the reported all‐electron DFT calculations, effective core potential (ECP) methods, GFN0‐xTB, GFN1‐xTB, GFN2‐xTB, RM1, Sparkle/RM1, Sparkle/AM1, Sparkle/PM n ( n = 3, 6, 7), HF, MP2, CCSD(T) methods and experimental data. The results show that Ln‐xTB successfully optimizes lanthanide compound structures with an average mean absolute deviation (MAD) of 0.037 Å for bond lengths relative to all‐electron DFT, outperforming GFN2‐xTB (MAD = 0.134 Å) and approaching the accuracy of ECP methods (MAD = 0.024 Å). Relative errors in bond lengths of Ln‐xTB are predominantly within 3% (vs. all‐electron DFT) and 5% (vs. experimental data). The results of benchmarks indicate the newly developed Ln‐xTB method is more accurate than the previously reported GFN n ‐xTB ( n = 0, 1, 2) methods. The structure optimization of lanthanide complexes with hundreds of atoms by using the Ln‐xTB was completed in several seconds on a single CPU core. This work provides a set of accurate, efficient Ln‐xTB parameters, addressing the long‐standing trade‐off between precision and computational cost in lanthanide molecular chemistry.