Dresden 2011 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 35: Joint Session: Organic Semiconductors II: Solar Cells B
HL 35.2: Talk
Tuesday, March 15, 2011, 11:00–11:15, ZEU 222
Performance of density functional theory for donor-acceptor systems: a case study for TTF and TCNQ molecules — •Viktor Atalla1, Mina Yoon1,2, and Matthias Scheffler1 — 1Fritz-Haber-Institut der MPG, Berlin, Germany — 2Oak Ridge National Laboratory, USA
Organic materials are promising candidates for a next generation of electronic devices, since they offer a variety of new intriguing properties. However, from a theoretical point of view these materials are challenging because they are often composed of donor-acceptor systems, for which density-functional theory (DFT) with state-of-the-art exchange-correlation (XC) functionals is often suspected to fail. Here we study the performance of DFT in describing electron affinities, ionization potentials, and charge transfer for clusters of the prototypical electron donor molecule TTF and acceptor molecule TCNQ.
For the indivdual molecules we calculate the dependence of the HOMO and LUMO levels on the fraction of exact exchange and the screening length [1]. We find that conventional semilocal and hybrid XC functionals severely underestimate HOMO-LUMO gaps. For weakly bound TTF-TCNQ dimers all investigated XC functionals consistently give charge transfer from the donor to the acceptor, however the amount of transfered charge is strongly functional dependent - in particular all semilocal functionals have significant aritificial charge transfer in the asymptotic limit.
[1] A. Krukau et al., J. Chem. Phys. 125, 2006