Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 61: Frontiers of Electronic Structure Theory: Organics and Materials (jointly with O, HL)

TT 61.3: Talk

Wednesday, March 18, 2015, 11:15–11:30, MA 004

Transition paths and cohesive energies in alpha-sexithiophene polymorphs — •Bernhard Klett, Caterina Cocchi, and Claudia Draxl — Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Germany

Like many organic crystals, oligothiophenes display polymorphism. Different molecular orientations and stacking arrangements are known to influence electronic and transport properties. An in-depth theoretical understanding of the energetics in these systems is crucial to control their growth and fully exploit their potential. In fact, their outstanding opto-electronic features make oligothiophenes excellent candidates for a number of technological applications, ranging from thin-film transistors to photovoltaic cells. We investigate alpha-sexithiophene in view of the transition between the high-temperature (HT) and low-temperature (LT) phase. With the full-potential all-electron density-functional theory code exciting [1], we analyse the cohesive properties of the two polymorphs. Our results indicate HT as the most stable phase, in agreement with previous molecular-dynamics simulations [2]. We also explore a transition path between the two polymorphs, suggesting different reaction coordinates. Our findings allow for estimating the energy barrier between the two phases, hence gaining insight into the microscopic mechanisms ruling polymorphism in organic crystals. [1] A. Gulans, et al., J. Phys.: Condens. Matter 26, 363202 (2014). [2] R. G. Della Valle, et al., J. Phys. Chem. A, 112, 6715 (2008).