Browsing by Author "Elstner, Marcus"

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Automatized Parametrization of SCC-DFTB Repulsive Potentials: Application to Hydrocarbons
(2009-10-29)
Gaus, Michael
;
Chou, Chien-Pin
;
Witek, Henryk
;
Elstner, Marcus
;
應用化學系
In this work, we derive and test a new automatized strategy to construct repulsive potentials for the self-consistent charge density functional tight-binding (SCC-DFTB) method. This approach allows one to explore the parameter space in a systematic fashion in order to find optimal solutions. We find that due to the limited flexibility of the SCC-DFTB electronic part, not all properties can be optimized simultaneously. For example, the optimization of heats of formation is in conflict with the optimization of vibrational frequencies. Therefore, a special parametrization, for vibrational frequencies is derived. It is shown that the performance of SCC-DFTB can be significantly improved using a more elaborate fitting strategy. A new fit for C and H is presented, which results in an average error of 2.6 kcal/mol for heats of formations for a large set of hydrocarbons, indicating that the performance of SCC-DFTB can be systematically improved also for other elements.
Relativistic parametrization of the self-consistent-charge density-functional tight-binding method. 1. Atomic wave functions and energies
(2007-07-05)
Witek, Henryk A.
;
Koehler, Christof
;
Frauenheim, Thomas
;
Morokuma, Keiji
;
Elstner, Marcus
A detailed treatment of a confined relativistic atom, needed as an initial step for the parametrization of the self-consistent-charge density-functional tight-binding method, is presented and discussed. The required one-component quantities, i.e., orbital energies, orbital wave functions, and Hubbard parameters, are obtained by weighted averaging of the corresponding numbers determined for the atomic spinors. The wave function and density confinement is achieved by introducing the Woods-Saxon potential in the atomic four-component Dirac-Kohn-Sham problem. The effect of the additional confining potential on energy eigenvalues and the shape of atomic wave functions and densities is discussed and numerical examples are presented for the valence spinors of carbon, germanium, and lead.