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XTB

Overview

XTB method 1. Full documentation available at the XTB website.
The NWChem implementation makes use of the TBlite library. 

 XTB
   [ACC <real acc default 1.0>] 
   [UHF <integer uhf default 0>]
   [METHOD gfn1 || gfn2 default gfn2]
   [GUESS]
   [VERBOSITY]
   [PRINT]  
   [NOPRINT]
   [NSPIN <integer nspin default 1>]
   [BROYDEN <real broyden default 0.4>]
 END

ACC: Accuracy

For example, if the user wants to increase the accuracy:

 acc 1d-4

UHF: number of unpaired electrons

 uhf 3

NSPIN:

A value of nspin equal to two triggers an open-shell calculation (while the default value of 1 triggers a closed-shell calculation).

 nspin 2

References

  1. Bannwarth, C.; Caldeweyher, E.; Ehlert, S.; Hansen, A.; Pracht, P.; Seibert, J.; Spicher, S.; Grimme, S. Extended Tight-Binding Quantum Chemistry Methods. WIREs Computational Molecular Science 2020, 11 (2). https://doi.org/10.1002/wcms.1493. ↩