# User Guide to Semiempirical Tight Binding¶

This user guide focuses on the semiempirical quantum mechanical methods GFNn-xTB, their descendants, and corresponding composite schemes as implemented in the xtb (extended tight binding) program package.

We provide a number of detailed guides dealing with common task that can
be performed easily with the `xtb`

program.
All guides are usually structured the same way, starting with some simple
examples using only the commandline and the default settings followed
by a trouble shooting section.
Detailed inputs are provided in a ready to use fashion to solve some
more special but still common tasks with `xtb`

together with some
insights into the theory used behind the scences.

## Quick Links¶

## Recent developments, news and publications¶

2021-06-10: xtb version 6.4.1 released by

*Sebastian Ehlert*We released a new version of

`xtb`

with a significantly improved memory footprint for large scale calculations and improved parallelisation for frequency calculations. The parallel evaluation of hessians with GFN-FF is now possible, overall we improved the stablility of the parallelisation which was slightly degraded in version 6.4.0. For xTB calculations the required`OMP_STACKSIZE`

has been significantly reduced by restructuring the integral evaluation slightly.Also, this version of

`xtb`

now supports the COSMO/CPCM solvation model using the ddPCM library.2021-06-10: QCxMS version 5.0.3 released by

*Jeroen Koopman*Recently, we released the QCxMS program for calculating EI and CID mass spectra using molecular dynamics. The project moved to GitHub under the @qcxms namespace and will soon become an open source project, as soon as all major bugs are fixed.

In this second update, we have started to update the output information provided by the program and especially the cid module and improved the way the automated

*general run-type*of the CID module detemines the number of collisions. This in turn leads to a**greater number**of collisions in the simulation than in the versions before.2021-05-03: DFT-D4 version 3.2.0 released by

*Sebastian Ehlert*We released a new version of DFT-D4 further expanding the functionality of the Python API and the integration with QCEngine and ASE. In this process we simplified the installation of the Python extension module which should now also be possible with pip. The DFT-D4 program can now also calculate pairwise resolved dispersion energies, both for the pairwise additive and pairwise non-additive contributions to the total dispersion energy.

Find the complete release notes here.

See the news archive for all posts.

## xTB in Other Quantum Chemistry Programs¶

The xTB-methods are now officially available in other quantum chemistry programs!

in Orca 4.2 an IO-based interface to the

`xtb`

binary is availableAMS 2019 implements GFN1-xTB in their DFTB module

the entos program implements GFN1-xTB (also available in the webinterface)

the computational chemistry framework cuby4 supports

`xtb`

Turbomole does support GFN1-xTB and GFN2-xTB since version 7.4

QCEngine supports calculations with the

`xtb`

APIthe GMIN, OPTIM, and PATHSAMPLE global optimization tools provide a

`xtb`

interfaceCP2K has an GFN1-xTB implementation since version 7.1

We missed your project here? No problem, just give us hint at the mailing list or open an issue at github.

- Singlepoint Calculations
- Properties
- Geometry Optimization
- Exploration of the potential energy surface (PES)
- Implicit Solvation
- Calculation of Vibrational Frequencies
- Molecular Dyamics Simulations
- Meta-Dynamics Simulations
- Reaction Path Methods
- Growing String Method
- Periodic Boundary Conditions
- External Potentials and Embedding
- GFN-Force-Field (GFN-FF)
- C API to the extended tight binding program
- Python Integration for the xtb API
- Community resources

- Introduction to CREST
- CREST Versions and Changelog
- CREST command line arguments
- Example applications
- iMTD-GC conformational search
- Sorting an ensemble
- Comparing two ensemble
- Constrained conformational sampling
- Sampling of noncovalent complexes and aggregates (NCI mode)
- Molecular prototropy screening
- Property calculations on final ensemble
- Dry run to check settings prior to calculations
- Examples from the paper: Automated exploration of the low-energy chemical space with fast quantum chemical methods
- Preparing a Nanoreactor calculation for
`xtb`