A Robust and Broadly Parametrized Non-Selfconsistent Tight Binding Quantum Chemistry Method for Extended Systems

Sebastian Ehlert, Eike Caldeweyher, Philipp Pracht, and Stefan Grimme
University of Bonn, Germany

A new semiempirical quantum mechanical method is presented, which is designed for the fast calculation of geometries, frequencies and non-covalent interaction energies (GFN) for extended systems with a few thousand atoms. In contrast to the established DFTB and recent extended tight binding (xTB) methods (GFN1-xTB [1] and GFN2-xTB [2]), the new method, termed GFN0-xTB [3] avoids the self-consistent charge iterations but solves the electronic structure non-selfconsistently by incorporation only first-order contributions in the Hamiltonian. The essential electronic electrostatic interactions are treated by a classical, second-order electronegativity equilibration model. This results in speedups of about 2–20 compared to GFN1/2-xTB. While GFN0-xTB is inherently slightly less accurate than other xTB methods it can describe the structure of relatively complicated transition metal complexes well and is also able to accurately reproduce zeolite framework structures, which pose difficulties for most self-consistent tight binding methods. Due to its low computational cost GFN0-xTB is especially useful for estimating relative thermostatistical reaction free energies even for extended periodic systems. The GFN0-xTB method relies solely on element-specific and global parameters. Currently, parameters for the entire periodic table up to radon (Z=86) are readily available. The computational efficiency along with its
robustness make this method well-suited to explore conformational space of large molecular systems or model polymorphs for condensed phase systems.

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