General¶

Introduction¶

Our implementation of the DFTB method can perform single point calculations, geometry optimizations, transition state searches, frequency calculations, and molecular dynamics. Molecules as well as periodic systems can be handled ensuring a smooth link with our full DFT codes ADF and BAND. It can be used from the command line through the AMS driver, or through the graphical interface.

The DFTB program is orders of magnitude faster than DFT, but requires parameter files for all pair-wise combinations of atoms in a molecule. Many elements can be handled with the parameter sets included in the distribution. Alternatively, sets of parameters in the SKF format can be downloaded and used from third party sources.

Three models within the DFTB framework are available: standard DFTB, SCC-DFTB (DFTB with self-consistent-charge correction), and DFTB3 (SCC-DFTB with third-order correction). As they have been respectively parametrized, it is important to specify a proper parameter set when applying one of these models.

What’s new in DFTB 2018¶

New features¶

• Elastic tensor and related properties (e.g. Bulk modulus) (via AMS)
• Linear transit and PES scan (via AMS)
• Geometry optimization under pressure (via AMS)
• ...

AMS: a new driver program¶

Important

In the 2018 release of the Amsterdam Modeling Suite we introduced a new driver program call AMS. We recommend you to first read the General section of the AMS Manual

If you use DFTB exclusively via the Graphical User Interface (GUI), this change should not create any issues. If, on the other hand, you create input files by hand (or you use DFTB via PLAMS), then you should be aware that shell scripts for DFTB-2017 and previous versions are not compatible with DFTB-2018 and have to be adjusted to the new setup.

The example below shows how a shell script for DFTB-2017 is converted to DFTB-2018.

DFTB-2017 shell script (obsolete):

#!/bin/sh

# This is a shell script for DFTB-2017 which will not work for DFTB-2018

$ADFBIN/dftb << EOF Task RunType GO End System Atoms H 0.0 0.0 0.0 H 0.9 0.0 0.0 End End DFTB ResourcesDir Dresden End Geometry iterations 100 End EOF  DFTB-2018 shell script: #!/bin/sh # This is a shell script for DFTB-2018 # The executable '$ADFBIN/dftb' is no longer present.
# You should use '$ADFBIN/ams' instead.$ADFBIN/ams << EOF
# Input options for the AMS driver:

System
Atoms
H 0.0 0.0 0.0
H 0.9 0.0 0.0
End
End