An efficient implementation of Density-Functional based Tight-Binding method
(DFTB) in Gaussian 03 program: The calculation of energies, gradients,
vibrational frequencies and IR spectrums

Guishan Zheng, gzheng@emory.edu1, Michael Frisch2, and Keiji Morokuma,
morokuma@emory.edu1. (1) Cherry L. Emerson Center for Scientific Computation and
Department of Chemistry, Emory University, 1515 Dickey Dr, Atlanta, GA 30322,
(2) Gaussian, Inc, 340 Quinnipiac St Bldg 40, Wallingford, CT 06492

We have recently implemented the energy, analytical gradient and frequencies as
well as IR intensities of the closed shell and the spin-polarized (s-)DFTB (with
or without the dispersion contribution(-D)) in the Gaussian program. Several new
aspects have been included: 1) For diatomic parameters, using analytical
functions consisting of even-tempered polynomials and fitted to the original
parameters; 2) Removal of unphysical oscillation of diatomic overlap and
Hamiltonian matrix element values in the original parameter tables at long
distance; 3) New scheme for the gamma matrix element for two center
charge-charge interactions. These are intended to improve the numerical
accuracy. Parameters for transition metal elements, recently developed by the
Morokuma group, are also incorporated.