We solve the long-standing problem of the large overestimation of the static polarizability of conjugated polymers obtained using the local density approximation within density-functional theory. The local approximation is unable to describe the highly nonlocal exchange and correlation (xc) effects found in these quasi-one-dimensional systems. Time-dependent current-density-functional theory enables a local current description of ultranonlocal xc effects using the Vignale-Kohn functional [G. Vignale and W. Kohn, Phys. Rev. Lett. 77, 2037 (1996)]. Except for the model hydrogen chain, our results are in excellent agreement with the best available correlated methods.

In this paper we present a new approach to calculate optical spectra, which for the first time uses a polarization dependent functional within current density functional theory (CDFT), which was proposed by Vignale and Kohn [Phys. Rev. Lett. 77, 2037 (1996)]. This polarization dependent functional includes exchange-correlation (xc) contributions in the effective macroscopic electric field. This functional is used to calculate the optical absorption spectrum of several common semiconductors. We achieved in all cases good agreement with experiment.

Efficient real-space approach to time-dependent density functional theory for the dielectric response of nonmetallic crystals Kootstra, F.; de Boeij, P. L.; Snijders, J. G. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Time-dependent density functional theory has been used to calculate the static and frequency-dependent dielectric function ⑀( ) of nonmetallic crystals. We show that a real-space description becomes feasible for crystals by using a combination of a lattice-periodic ͑microscopic͒ scalar potential with a uniform ͑macroscopic͒ electric field as perturbation in a periodic structure calculation. The induced density and microscopic potential can be obtained self-consistently for fixed macroscopic field by using linear response theory in which Coulomb interactions and exchange-correlation effects are included. We use an iterative scheme, in which density and potential are updated in every cycle. The explicit evaluation of Kohn-Sham response kernels is avoided and their singular behavior as function of the frequency is treated analytically. Coulomb integrals are evaluated efficiently using auxiliary fitfunctions and we apply a screening technique for the lattice sums. The dielectric function can then be obtained from the induced current. We obtained ⑀( ) for C, Si, and GaAs within the adiabatic local density approximation in good agreement with experiment. In particular in the low-frequency range no adjustment of the local density approximation ͑LDA͒ band gap seems to be necessary.

Articles you may be interested inDetermining the appropriate exchange-correlation functional for time-dependent density functional theory studies of charge-transfer excitations in organic dyes Assessment of exchange-correlation functionals for the calculation of dynamical properties of small clusters in time-dependent density functional theoryWe provide a successful approach towards the solution of the longstanding problem of the large overestimation of the static polarizability of conjugated oligomers obtained using the local density approximation within density-functional theory. The local approximation is unable to describe the highly nonlocal exchange and correlation effects found in these quasi-one-dimensional systems. Time-dependent current-density-functional theory enables us to describe ultranonlocal exchange-correlation effects within a local current description. Recently a brief account was given of the application of the Vignale-Kohn current-functional ͓G. Vignale and W. Kohn, Phys. Rev. Lett. 77, 2037 ͑1996͔͒ to the axial polarizability of oligomer chains ͓M. van Faassen, P. L. de Boeij, R. van Leeuwen, J. A. Berger, and J. G. Snijders, Phys. Rev. Lett. 88, 186401 ͑2002͔͒. With the exception of the model hydrogen chain, our results were in excellent agreement with best available wavefunction methods. In the present work we further outline the underlying theory and describe how the Vignale-Kohn functional was implemented. We elaborate on earlier results and present new results for the oligomers of polyethylene, polysilane, polysilene, polymethineimine, and polybutatriene. The adiabatic local density approximation gave good results for polyethylene, which were slightly modified by the Vignale-Kohn functional. In all other cases the Vignale-Kohn functional gave large improvements upon the adiabatic local density approximation. The Vignale-Kohn results were in agreement with best available data from wave function methods. We further analyze the hydrogen chain model for different bond length alternations. In all these cases the Vignale-Kohn correction upon the adiabatic local density approximation was too small. Arguments are given that further improvements of the functional are needed.

Application of time-dependent density-functional theory to the dielectric function of various nonmetallic crystals Kootstra, F.; de Boeij, P.L.; Snijders, J.G.