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.
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.
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.
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: 10 May 2009