Mark A. Iron, Grażyna Staszewska, Tiqing Liu, Ahren W. Jasper, and Donald G. Truhlar
Department of Chemistry and Supercomputer Institute
University of Minnesota, Minneapolis, Minnesota 55455-0431
TBPAC is a complete package for tight binding calculations on molecules containing selected metal atoms (Al, Ni, Cu, Pd, Ag, Pt, and Au) plus carbon and hydrogen. This implementation combines the capabilities of TB 1.0 and TB 2.0 plus it adds tight-binding with a Hubbard-like term (TB+U), and tight binding with configuration interaction (TBCI). As a result, it includes orthogonal and nonorthogonal Slater-Koster tight binding, penalty energies, orthogonal and nonorthogonal many-body tight binding, tight-binding with a Hubbard-like term, and tight binding with configuration interaction. (None of the methods is supported for all possible combinations of the supported elements.) Analytical gradients are available for all methods.
TBPAC is a FORTRAN 77 computer program for the calculation of potential energy surfaces and analytical gradients of systems involving Ni, Cu, Pd, Ag, Pt, or Au and C and/or H by using tight binding theory. Tight binding theory is a highly parametrized extended Hueckel theory, and the present implementation includes an explicit term representing the pairwise repulsion between atomic cores. The present code also includes a Hubbard-type penalty term. The overlap integral is not included in the secular equation. The radial parts of the Hamiltonian matrix elements are parametrized using the functional forms of Lathiotakis et al. and Wang and Mak or the Wolfberg-Holmholz scheme; the angular parts are evaluated by the Slater-Koster scheme. The program is built as a subroutine accepting the coordinates of the system from the caller and returning the energy of the system and the first derivatives of the energy with respect to the Cartesian coordinates of each atom in the system.
TBPAC also contains tight binding methods solely designed for homonuclear systems composed of Al atoms. The dimension of the matrix is 4*N, where N is the number of Al atoms in the nanoparticle, and electronic wave functions are expanded in a basis of 4 atomic orbitals: 3s,3p_x,3p_y and 3p_z; Al has 3 valence electrons. The code may be applied to neutral clusters.
The radial parts of the Hamiltonian matrix elements are parametrized in 6 different ways as described in:
Grażyna Staszewska, Przemysław Staszewski, Nathan E. Schultz and Donald G. Truhlar, "Many-body tight binding model for aluminum nanoparticles," Physical Reviews B, 71, 045423 (2005) (Read at APS)
(1) MBTB-S - many-body tight-binding based on screening,
(2) MBTB-CN - many-body tight-binding based on coordination number,
(3) MBTB-BA - Many-body tight-binding based on bond-angle correction,
and three versions of pair-wise tight binding:
(4) TB-OWH - optimized Wolfsberg-Helmholz approximation
(5) TB-EWH - extended Wolfsberg-Helmholz approximation
(6) TB-WH - Wolfsberg-Helmholz approximation.
The angular parts are evaluated by the Slater-Koster scheme. The current version is available for energies only and does not include analytical gradients.