Analytical excited state forces for the time-dependent density-functional tight-binding method.
An analytical formulation for the geometrical derivatives of excitation energies within the time-dependent density-functional tight-binding (TD-DFTB) method is presented. The derivation is based on the auxiliary functional approach proposed in [Furche and Ahlrichs, J Chem Phys 2002, 117, 7433]. To validate the quality of the potential energy surfaces provided by the method, adiabatic excitation energies, excited state geometries, and harmonic vibrational frequencies were calculated for a test set of molecules in excited states of different symmetry and multiplicity. According to the results, the TD-DFTB scheme surpasses the performance of configuration interaction singles and the random phase approximation but has a lower quality than ab initio time-dependent density-functional theory. As a consequence of the special form of the approximations made in TD-DFTB, the scaling exponent of the method can be reduced to three, similar to the ground state. The low scaling prefactor and the satisfactory accuracy of the method makes TD-DFTB especially suitable for molecular dynamics simulations of dozens of atoms as well as for the computation of luminescence spectra of systems containing hundreds of atoms.
Heringer
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General Electrics, Consumer & Industrial--Lighting, 1340 Budapest, Vaci ut 77, Hungary.
Niehaus
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Wanko
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Frauenheim
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D002734:Chlorophyll; D053279:Polyynes; D015016:Yohimbine; D017239:Paclitaxel; D001241:Aspirin; D000077194:Chlorophyll A