DFTB
DFTBA

DESCRIPTION

Requests a density-functional based tight-binding semi-empirical calculation, a method which is parametrized via the results of DFT calculations. DFTB uses the tabulated matrix elements as in the original implementation of Elstner and coworkers [Porezag95, Elstner98]; DFTBA is a version which uses analytic expressions for the matrix elements rather than tabulated ones [Zheng07]. See [Frauenheim00, Frauenheim02, Zheng05, Sattelmeyer06, Otte07] for review articles and calibration studies.

OPTIONS

There are no internally stored parameters for these methods, so one of the following options must be specified.

ReadParameters
Read values for parameters from the input stream.

ChkParameters
Read parameters from the checkpoint file.

AVAILABILITY

Energies, gradients and frequencies.

DFTBA is parametrized for all pairs of H, C, N, and O. It is also parametrized for the metals Sc, Ti, Fe, Co, and Ni but only with H, C, N, and O. That is, Fe₅CO and Sc₅CO are supported, but Fe₄ScCO is not. The DFTB parameter files are copyright by Professor Elstner and must be obtained from him.

EXAMPLES

The following input file format runs a DFTBA calculation using the parameter set provided with Gaussian 09:

# DFTBA OPT FREQ

Ala3 DFTB frequencies

0,1
C,0,-4.5929012011,1.0163256276,1.6498020765
O,0,-5.6641782096,0.9622594116,2.2369288649
H,0,-5.788876035,3.2375262156,-2.1703220199
N,0,-4.4446298947,1.4038535552,0.3517633631
Molecule specification continues …
 
@GAUSS_EXEDIR:dftba.prm

For DFTB, the same format of parameter files is used as in other programs: one file for each pair of elements, with the order of the two elements being significant. Accordingly, a calculation on H₂CO would use a parameter input section something like this:

@cc.prm
@oo.prm
@hh.prm
@co.prm
@oc.prm
@ch.prm
@hc.prm
@oh.prm
@ho.prm

The DFTB energy appears in the output as follows:

 SCF Done:  E(RDFT-SCTBA) =  -33.9465130617     A.U. after   11 cycles

Last updated on: 13 May 2010