NAME

       xtb - performs semiempirical quantummechanical calculations, for version 6.0 and newer

SYNOPSIS

       xtb [OPTIONS] FILE [OPTIONS]

DESCRIPTION

       The xtb(1) program performs semiempirical quantummechanical calculations. The underlying effective
       Hamiltonian is derived from density functional tight binding (DFTB). This implementation of the xTB
       Hamiltonian is currently compatible with the zeroth, first and second level parametrisation for
       geometries, frequencies and non-covalent interactions (GFN) as well as with the ionisation potential and
       electron affinity (IPEA) parametrisation of the GFN1 Hamiltonian. The generalized born (GB) model with
       solvent accessable surface area (SASA) is also available in this version. Ground state calculations for
       the simplified Tamm-Dancoff approximation (sTDA) with the vTB model are currently not implemented.

   GEOMETRY INPUT
       The wide variety of input formats for the geometry are supported by using the mctc-lib. Supported formats
       are:

       •   Xmol/xyz files (xyz, log)

       •   Turbomole’s coord, riper’s periodic coord (tmol, coord)

       •   DFTB+ genFormat geometry inputs as cluster, supercell or fractional (gen)

       •   VASP’s POSCAR/CONTCAR input files (vasp, poscar, contcar)

       •   Protein Database files, only single files (pdb)

       •   Connection table files, molfile (mol) and structure data format (sdf)

       •   Gaussian’s external program input (ein)

       •   JSON input with qcschema_molecule or qcschema_input structure (json)

       •   FHI-AIMS' input files (geometry.in)

       •   Q-Chem molecule block inputs (qchem)

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

       xtb(1) reads additionally .CHRG and .UHF files if present.

INPUT SOURCES

       xtb(1) gets its information from different sources. The one with highest priority is the commandline with
       all allowed flags and arguments described below. The secondary source is the xcontrol(7) system, which
       can in principle use as many input files as wished. The xcontrol(7) system is the successor of the
       set-block as present in version 5.8.2 and earlier. This implementation of xtb(1) reads the xcontrol(7)
       from two of three possible sources, the local xcontrol file or the FILE used to specify the geometry and
       the global configuration file found in the XTBPATH.

OPTIONS

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

       -c, --chrg INT:INT
           specify charges for inner region:outer region for oniom calculation, overrides .CHRG file and
           xcontrol option

       -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

       --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 high:low where high can be orca,
           turbomole, gfn2, gfn1, or gfnff and low can be gfn2, gfn1, or gfnff. The inner region is given as
           comma-separated indices directly in the commandline or in a file with each index on a separate line.

       --etemp, --temp REAL
           electronic temperature for SCC (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)

       --iterations, --maxiterations INT
           maximum number of SCC iterations per single point calculation (default = 250)

       --vparam FILE
           Parameter file for xTB calculation

       --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 or bar1M
           (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 or bar1M (default).

       --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

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

       --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)

       --dipole
           requests dipole printout

       --wbo
           requests Wiberg bond order printout

       --lmo
           requests localization of orbitals

       --fod
           requests FOD calculation

   RUNTYPS
           Note

           You can only select one runtyp, only the first runtyp will be used from the program, use implemented
           composite runtyps to perform several operations at once.

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

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

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

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

       --vfukui
           performs calculation of Fukui indices.

       --vomega
           performs calculation of electrophilicity index. This needs the .param_ipea.xtb 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

       --reactor
           experimental

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

       --dipro [REAL]
           the dimer projection method for the calculation of electronic coupling integrals between two
           fragments.  REAL sets the threshold for nearly degenerate orbitals to still be considered (default =
           0.1 eV).

   GENERAL
       -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 (e.g. xtbtopo.mol)

       --strict
           turns all warnings into hard errors

       -h, --help
           show help page

       --cut
           create inner region for oniom calculation without performing any calcultion

ENVIRONMENT VARIABLES

       xtb(1) accesses a path-like variable to determine the location of its parameter files, you have to
       provide the XTBPATH variable in the same syntax as the system PATH variable. If this variable is not set,
       xtb(1) will try to generate the XTBPATH from the deprecated XTBHOME variable. In case the XTBHOME
       variable is not set it will be generated from the HOME variable. So in principle storing the parameter
       files in the users home directory is suffient but might lead to come cluttering.

       Since the XTBHOME variable is deprecated with version 6.0 and newer xtb(1) will issue a warning if
       XTBHOME is not part of the XTBPATH since the XTBHOME variable is not used in production runs.

LOCAL FILES

       xtb(1) accesses a number of local files in the current working directory and also writes some output in
       specific files. Note that not all input and output files allow the --namespace option.

   INPUT
       .CHRG
           molecular charge as int

       .UHF
           Number of unpaired electrons as int

       mdrestart
           contains restart information for MD, --namespace compatible.

       pcharge
           point charge input, format is real real real real [int]. The first real is used as partial charge,
           the next three entries are the cartesian coordinates and the last is an optional atom type. Note that
           the point charge input is not affected by a CMA transformation. Also parallel Hessian calculations
           will fail due to I/O errors when using point charge embedding.

       xcontrol
           default input file in --copy mode, see xcontrol(7) for details, set by --input.

       xtbrestart
           contains restart information for SCC, --namespace compatible.

   OUTPUT
       charges
           contains Mulliken partial charges calculated in SCC

       wbo
           contains Wiberg bond order calculated in SCC, --namespace compatible.

       energy
           total energy in Turbomole format

       gradient
           geometry, energy and gradient in Turbomole format

       hessian
           contains the (not mass weighted) cartesian Hessian, --namespace compatible.

       xtbtopo.mol
           topology information written in molfile format.

       xtbopt.xyz, xtbopt.coord
           optimized geometry in the same format as the input geometry.

       xtbhess.coord
           distorted geometry if imaginary frequency was found

       xtbopt.log
           contains all structures obtained in the geometry optimization with the respective energy in the
           comment line in a XMOL formatted trajectory

       xtbsiman.log,xtb.trj.int
           trajectories from MD

       scoord.int
           coordinate dump of MD

       fod.cub
           FOD on a cube-type grid

       spindensity.cub
           spindensity on a cube-type grid

       density.cub
           density on a cube-type grid

       molden.input
           MOs and occupation for visualisation and sTDA-xTB calculations

       pcgrad
           gradient of the point charges

       xtb_esp.cosmo
           ESP fake cosmo output

       xtb_esp_profile.dat
           ESP histogramm data

       vibspectrum
           Turbomole style vibrational spectrum data group

       g98.out, g98l.out, g98_canmode.out, g98_locmode.out
           g98 fake output with normal or local modes

       .tmpxtbmodef
           input for mode following

       coordprot.0
           protonated species

       xtblmoinfo
           centers of the localized molecular orbitals

       lmocent.coord
           centers of the localized molecular orbitals

       tmpxx
           number of recommended modes for mode following

       xtb_normalmodes, xtb_localmodes
           binary dump for mode following

   TOUCH
       xtbmdok
           generated by successful MD

       .xtbok
           generated after each successful xtb(1) run

       .sccnotconverged
           generated after failed SCC with printlevel=2

WARNINGS

       xtb(1) can generate the two types of warnings, the first warning section is printed immediately after the
       normal banner at startup, summing up the evaluation of all input sources (commandline, xcontrol, xtbrc).
       To check this warnings exclusively before running an expensive calculation a input check is implemented
       via the --define flag. Please, study this warnings carefully!

       After xtb(1) has evaluated the all input sources it immediately enters the production mode. Severe errors
       will lead to an abnormal termination which is signalled by the printout to STDERR and a non-zero return
       value (usually 128). All non-fatal errors are summerized in the end of the calculation in one block,
       right before the timing analysis.

       To aid the user to fix the problems generating these warnings a brief summary of each warning with its
       respective string representation in the output will be shown here:

       ANCopt failed to converge the optimization
           geometry optimization has failed to converge in the given number optimization cycles. This is not
           neccessary a problem if only a small number of cycles was given for the optimization on purpose. All
           further calculations are done on the last geometry of the optimization.

       Hessian on incompletely optimized geometry!
           This warning will be issued twice, once before the Hessian, calculations starts (it would otherwise
           take some time before this this warning could be detected) and in the warning block in the end. The
           warning will be generated if the gradient norm on the given geometry is higher than a certain
           threshold.

EXIT STATUS

       0
           normal termination of xtb(1)

       128
           Failure (termination via error stop generates 128 as return value)

BUGS

       please report all bugs with an example input, --copy dump of internal settings and the used geometry, as
       well as the --verbose output to xtb@thch.uni-bonn.de

RESOURCES

       Main web site: http://grimme.uni-bonn.de/software/xtb

COPYING

       Copyright © 2017-2023 Stefan Grimme

       xtb is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General
       Public License as published by the Free Software Foundation, either version 3 of the License, or (at your
       option) any later version.

       xtb is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
       warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
       License for more details.

       You should have received a copy of the GNU Lesser General Public License along with xtb. If not, see
       https://www.gnu.org/licenses/.

                                                   03/26/2024                                             XTB(1)