Usage: xtb [options] <geometry> [options]

<geometry> may be provided as valid TM coordinate file (*coord in Bohr),
in xmol format (*.xyz in Ångström), sdf or mol file format, PDB format
genFormat input or Vasp's POSCAR format.

For a full list visit: https://grimme-lab.github.io/mctc-lib/page/index.html

Options:

-c, --chrg INT
    specify molecular charge as INT, overrides .CHRG file and xcontrol option

--ceh
    calculate CEH (Charge-Extended Hückel model) charges and write them to ceh.charges file

-u, --uhf INT
    specify number of unpaired electrons as INT, overrides .UHF file and xcontrol option

--gfn INT
    specify parametrisation of GFN-xTB (default = 2)

--gfnff, --gff
    specify parametrisation of GFN-FF

--tblite,
    use tblite library as implementation for xTB, please note that solvation is not yet implemented within tblite

--ptb,
    performs single-point calculation with the density tight-binding method PTB.
    Provides electronic structure and properties, such as, e.g., atomic charges, bond orders, and dipole moments,
    but does not provide any energy-related properties, such as, e.g., total energy, nuclear gradients, or vibrational frequencies.

--spinpol,
    enables spin-polarization for xTB methods (tblite required)

--oniom METHOD LIST
    use subtractive embedding via ONIOM method. 'METHOD' is given as 'inner:outer'
    where 'inner' can be 'orca', 'turbomole', 'gfn2', 'gfn1', or 'gfnff' and
    'outer' can be 'gfn2', 'gfn1', or 'gfnff'.
    The inner region is given as a comma separated indices directly in the commandline
    or in a file with each index on a separate line.

--etemp REAL
    electronic temperature (default = 300K)

--esp
    calculate electrostatic potential on VdW-grid

--stm
    calculate STM image

-a, --acc REAL
    accuracy for SCC calculation, lower is better (default = 1.0)

--vparam FILE
    Parameter file for vTB calculation

--xparam FILE
    Parameter file for xTB calculation (not used)

--alpb SOLVENT [STATE]
    analytical linearized Poisson-Boltzmann (ALPB) model,
    available solvents are acetone, acetonitrile, aniline, benzaldehyde,
    benzene, ch2cl2, chcl3, cs2, dioxane, dmf, dmso, ether, ethylacetate, furane,
    hexandecane, hexane, methanol, nitromethane, octanol, woctanol, phenol, toluene,
    thf, water.
    The solvent input is not case-sensitive. The Gsolv
    reference state can be chosen as reference, bar1M, or gsolv (default).

-g, --gbsa SOLVENT [STATE]
    generalized born (GB) model with solvent accessable surface (SASA) model,
    available solvents are acetone, acetonitrile, benzene (only GFN1-xTB), CH2Cl2,
    CHCl3, CS2, DMF (only GFN2-xTB), DMSO, ether, H2O, methanol,
    n-hexane (only GFN2-xTB), THF and toluene.
    The solvent input is not case-sensitive.
    The Gsolv reference state can be chosen as reference, bar1M, or gsolv (default).

--cosmo SOLVENT/EPSILON
    domain decomposition conductor-like screening model (ddCOSMO),
    available solvents are all solvents that are available for alpb.
    Additionally, the dielectric constant can be set manually or an ideal conductor
    can be chosen by setting epsilon to infinity.

--tmcosmo SOLVENT/EPSILON
    same as --cosmo, but uses TM convention for writing the .cosmo files.

--cpcmx SOLVENT
    extended conduction-like polarizable continuum solvation model (CPCM-X),
    available solvents are all solvents included in the Minnesota Solvation Database.

--cma
    shifts molecule to center of mass and transforms cartesian coordinates into the
    coordinate system of the principle axis (not affected by ‘isotopes’-file).

--pop
    requests printout of Mulliken population analysis

--molden
    requests printout of molden file

--dipole
    requests dipole printout

--raman
    requests Raman spectrum calculation via combination of GFN2-xTB and PTB
    using the temperature 'REAL' (default 298.15 K) and the wavelength of the
    incident laser which must be given in nm 'REAL' (default 514 nm).

--alpha
    requests the extension of electrical properties to static molecular dipole polarizabilities. 

--wbo
    requests Wiberg bond order printout

--lmo
    requests localization of orbitals

--fod
    requests FOD calculation

--scc, --sp
    performs a single point calculation

--vip
    performs calculation of ionisation potential. This needs the param_ipea-xtb.txt
    parameters and a GFN1 Hamiltonian.

--vea
    performs calculation of electron affinity. This needs the param_ipea-xtb.txt
    parameters and a GFN1 Hamiltonian.

--vipea
    performs calculation of electron affinity and ionisation potential.
    This needs the param_ipea-xtb.txt parameters and a GFN1 Hamiltonian.

--vfukui
    performs calculation of Fukui indices.

--vomega
    performs calculation of electrophilicity index. This needs the param_ipea-xtb.txt
    parameters and a GFN1 Hamiltonian.

--grad
    performs a gradient calculation

-o, --opt [LEVEL]
    call ancopt(3) to perform a geometry optimization, levels from crude, sloppy,
    loose, normal (default), tight, verytight to extreme can be chosen

--hess
    perform a numerical hessian calculation on input geometry

--ohess [LEVEL]
    perform a numerical hessian calculation on an ancopt(3) optimized geometry

--bhess [LEVEL]
    perform a biased numerical hessian calculation on an ancopt(3) optimized geometry

--md
    molecular dynamics simulation on start geometry

--metadyn [int]
    meta dynamics simulation on start geometry, saving int snapshots of the
    trajectory to bias the simulation

--omd
    molecular dynamics simulation on ancopt(3) optimized geometry,
    a loose optimization level will be chosen

--metaopt [LEVEL]
    call ancopt(3) to perform a geometry optimization, then try to find other
    minimas by meta dynamics

--path [FILE]
    use meta dynamics to calculate a path from the input geometry to the given
    product structure

--modef INT
    modefollowing algorithm. INT specifies the mode that should be used for the
    modefollowing.

-I, --input FILE
    use FILE as input source for xcontrol(7) instructions

--namespace STRING
    give this xtb(1) run a namespace. All files, even temporary ones, will be named
    according to STRING (might not work everywhere).

--[no]copy
    copies the xcontrol file at startup (default = true)

--[no]restart
    restarts calculation from xtbrestart (default = true)

-P, --parallel INT
    number of parallel processes

--define
    performs automatic check of input and terminate

--json
    write xtbout.json file

--citation
    print citation and terminate

--license
    print license and terminate

-v, --verbose
    be more verbose (not supported in every unit)

-s, --silent
    clutter the screen less (not supported in every unit)

--ceasefiles
    reduce the amount of output and files written

--strict
    turns all warnings into hard errors

-h, --help
    show help page

Useful Maschine Settings:

export MKL_NUM_THREADS=<NCORE>
export OMP_NUM_THREADS=<NCORE>,1
export OMP_STACKSIZE=4G
ulimit -s unlimited

Output Conventions:

total energies are given in atomic units (Eh)
gaps/HL energies are given in eV

More information can be obtained by `man 1 xtb` and `man 7 xcontrol`
or at https://xtb-docs.readthedocs.io/en/latest/contents.html

