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  and GFN2-xTB ), the new method, termed GFN0-xTB 
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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