TIME DEPENDENT DENSITY FUNCTIONAL THEORY ... - TDDFT.org

Plane-wave TDDFT calculations of molecules
in solution
Juerg Hutter
Physical Chemistry Institute, University of Zurich
A formulation of time dependent linear response density functional theory within the planewave
pseudopotential framework has recently been introduced [J. Hutter, J. Chem. Phys., 118,
3928 (2003)]. This implementation allows for efficient calculations of excitation spectra, excited
state properties and coupling to classical force fields in QM/MM approaches. The scheme has
been applied in combination with Car-Parrinello molecular dynamics to study the solvent shift
and intensity enhancement effects of the first electronic transition in acetone-water systems [L.
Bernasconi et al., J. Chem. Phys., 119, 12417 (2003)]. In agreement with experiment a general
increase in the mean oscillator strength and a blue shift of 0.19 eV of the transition was found.
However, this analysis was severely hampered by shortcomings of traditional density functionals.
Both, the poor eigenvalues of occupied and virtual Kohn-Sham orbitals and the lack of a correct
representation of charge transfer (CT) in the response kernel result in many unphysical solutesolvent
and solute-solute CT states overlapping with the acetone n-¿π ∗ transition. These problems
are partially solved using hybrid functional, although only with drastically increased computational
costs [L. Bernasconi et al., Chem. Phys. Lett., 394, 141 (2004)]. Another approach combines
standard DFT calculations with TDDFT using the statistical average of orbital model exchangecorrelation
potentials. The improved representation of orbital energies helps to isolate low-lying
local transitions and is a first step towards an accurate description of CT states.
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