FAQ
***


Which DFTB parameters are available?
====================================

The DFTB module in the Amsterdam Modeling Suite ships with the
following parameter sets:

* GFN1-xTB: extended tight-binding parameters for elements H-Rn (all
  spd elements). Can be used for all properties.

* Quasinano 2013: electronic parameters for H-Po, La, Th, enabling
  electronic properties like band structures, DOS, UV/VIS, NEGF.

* Quasinano 2015: + repulsive parameters for H-Ca, Br, enabling
  geometry optimization, IR spectra, MD.

* Dresden parameters: C, H, O, N, P, S, Al, Si, Ti, Cu, Na, see
  **$ADFHOME/atomicdata/DFTB/Dresden/README**

* DFTB.org parameters (see README or the DFTB.org website for latest
  info). Encrypted parameters may also be evaluated during a trial.

* Dispersion corrections available (Grimme’s D2 & D3(BJ), London,
  UFF).

See the documentation on the available DFTB parameter sets.


Can I use Grimme’s D3(BJ) dispersion corrections?
=================================================

Yes, with DFTB3 and either the Quasinano or the DFTB.org 3ob parameter
sets. With other DFTB methods and parameter sets you can use D2,
London (ULG), or UFF dispersion.


Do you have the extended Tight-Binding (xTB) parameters?
========================================================

We have implemented Grimme’s first GFN-xTB method (GFN1-xTB). The
second set (GFN2-xTB) usually does not improve accuracy much and has
not yet been implemented.


Can I include electric fields?
==============================

Yes.


Can I study 1D periodic systems like carbon nanotubes?
======================================================

Yes, DFTB can be applied to 0D systems (molecules), 1D systems
(polymers, nanotubes), 2D systems (surfaces), and 3D systems (bulk).

For 1D and 2D systems, we have proper periodic boundary conditions. So
you do not need to work with large unit cells and slab-gap
approximations.

All DFTB parameters can be used for any periodicity.
