This is a preliminary version of g-xTB, a general-purpose semiempirical quantum mechanical method approximating ωB97M-V/def2-TZVPPD properties.
See the preprint at ChemRxiv: https://chemrxiv.org/engage/chemrxiv/article-details/685434533ba0887c335fc974
Warning
gxtb currently works only on Linux-based machines.
Place the gxtb binary in a directory belonging to your $PATH variable (e.g., $USER/bin/).
Place the following parameter and basis files into your home directory (~/):
.gxtb— parameter file.eeq— electronegativity equilibration parameters.basisq— atom-in-molecule AO basis
By default, gxtb expects a coordinate file in TURBOMOLE format.
gxtb # default: coord file = TURBOMOLE format
gxtb -c <coord_file_name> # explicit coordinate file (TURBOMOLE or XYZ)
gxtb -c <xyz_file_name> # XYZ file supported
Place the following optional control files in your working directory:
.CHRG# Integer charge of the system (default: neutral).UHF# Integer number of open shells (e.g., 2 for triplet, 0 for singlet UKS)
If .CHRG or .UHF are not present:
- Even electrons: neutral singlet (RKS)
- Odd electrons: neutral doublet (UKS)
gxtb -grad
Or if a file named .GRAD is present, a numerical gradient is computed (expensive!).
Molecular symmetry is exploited to speed up calculations.
To optimize geometries using xtb with gxtb as a driver:
xtb struc.xyz --driver "gxtb -grad -c xtbdriver.xyz" --opt
Or with a coord file in TURBOMOLE format:
xtb coord --driver "gxtb -grad -c xtbdriver.coord" --opt
💡 You may use --opt loose for faster convergence, as there is currently no analytical nuclear gradient — gradients are evaluated numerically and can be noisy.
gxtb -hess
Computes a numerical Hessian (very expensive).
- Reasonably parameterized for elements Z = 1–58, 71–89, and 92
- A revised dispersion model (
revD4) is in progress and may slightly affect final results
- All computed properties aim to approximate ωB97M-V/def2-TZVPPD
- EEQ_BC charges mimic Hirshfeld charges from that reference
- Use the
-moldenflag to write a.moldenfile with orbitals and basis info:
gxtb -molden
Useful for visualization and post-processing.