Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K7: First-Principles Modeling of Excited State Phenomena IV: Molecular Systems and Singlet FissionFocus
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Sponsoring Units: DCOMP DMP DCP Chair: Noa Marom, Carnegie Mellon University Room: 266 |
Wednesday, March 15, 2017 8:00AM - 8:12AM |
K7.00001: Fine screening of high-performance organic photovoltaics Gian-Marco Rignanese, Nicolas Dardenne, Steven A. Lopez, Alan Aspuru-Guzik, Xavier Blase, Geoffroy Hautier, Jean-Christophe Charlier Organic photovoltaic (OPV) devices are a promising (cheap and versatile) technology for harvesting the solar energy. Their efficiency depends critically on the charge transfer (CT) effects taking place at the interface between electron donor and acceptor phases. In order to theoretically devise new OPV devices with high efficiency, it is thus important to describe these CT effects adequately. Tens of thousands of donor molecules have been already tested in a multiple-step screening within the Harvard Clean Energy Project (CEP), leading to a ranking of potential candidates. However, these calculations have been performed relying on density-functional theory. The latter is known to underestimate the band gap and not to describe electron-hole interaction and CT effects correctly. Here, we investigate the top 20 donor molecules from the CEP ranking using the $GW$/BSE formalism. [Preview Abstract] |
Wednesday, March 15, 2017 8:12AM - 8:24AM |
K7.00002: Explicit crystal host effects on excited state properties of linear polyacenes: towards a room-temperature maser Robert Charlton, Stuart Bogatko, Tim Zuehlsdorff, Nicholas Hine, Andrew Horsfield, Peter Haynes Maser technology has been held back for decades by the impracticality of the operating conditions of traditional masing devices, such as cryogenic freezing and strong magnetic fields. Recently it has been experimentally demonstrated that pentacene in \textit{p}-terphenyl can act as a viable solid-state room-temperature maser by exploiting the alignment of the low-lying singlet and triplet excited states of pentacene. To understand the operation of this device from first principles, an \textit{ab initio} study of the excitonic properties of pentacene in \textit{p}-terphenyl has been carried out using time-dependent density functional theory (TDDFT), implemented in the linear-scaling ONETEP software (www.onetep.org). In particular, we focus on the impact that the wider crystal has on the localised pentacene excitations by performing an explicit DFT treatment of the \textit{p}-terphenyl environment. We demonstrate the importance of explicit crystal host effects in calculating the excitation energies of pentacene in \textit{p}-terphenyl, providing important information for the operation of the maser. We then use this same approach to test the viability of other linear polyacenes as maser candidates as a screening step before experimental testing. [Preview Abstract] |
Wednesday, March 15, 2017 8:24AM - 8:36AM |
K7.00003: Nature of electronic excitations in pentaerythritol tetranitrate crystals doped with 9,10-phenanthrenequinone Guzel Garifzianova, Roman Tsyshevskiy, Anton Zverev, Anatoly Mitrofanov, Maija Kuklja Electronic properties, optical absorption and chemical reactivity of organic ketones and quinone molecules have been widely studied because of their ability to abstract hydrogen atoms from other organic molecules once excited to the highly reactive $^{3}$(n,$\pi $*) state. Most of these studies were done for liquid solutions. In this joint theoretical and experimental study, we focused on excited states of pentaerythritol tetranitrate (PETN) crystals doped with 9,10-phenanthrenequinone (PQ) molecules. We explored electronic properties of the system and estimated energies of the electronic excitations. It was found that PQ molecule in its excited triplet state can catalyze unusual decomposition pathways of PETN, which are not attainable through the potential surface of the ground state. We discuss mechanisms of such autocatalytic reactions in PETN-PQ complexes. [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 9:12AM |
K7.00004: Excited state dynamics in nanoscale materials: time-domain ab initio studies Invited Speaker: Oleg Prezhdo Photo-induced processes at interfaces are key to photovoltaic and photo-catalytic applications. They require understanding of dynamical response of novel materials on atomic and nanometer scales. Our non-adiabatic molecular dynamics techniques, implemented within time-dependent density functional theory, allow us to model such non-equilibrium response in real time. The talk will focus on photo-initiated charge and energy transfer in several classes of nanoscale materials. Examples include semiconductor surfaces sensitized with organic molecules, water, semiconductor quantum dots, graphene and perovskites, carbon nanotube bundles, mixtures of C60 with inorganic particles, etc. Photo-induced charge separation and recombination across such interfaces creates many challenges due to stark differences between molecular and periodic, and organic and inorganic systems. Our simulations provide a unifying description of quantum dynamics on nanoscale, characterize the rates and branching ratios of competing processes, resolve debated issues, and generate theoretical guidelines for development of novel systems for solar energy harvesting, electronics and other applications. [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:24AM |
K7.00005: Singlet-Fission from First-Principles Many-Body Perturbation Theory Sivan Refaely-Abramson, Felipe H. da Jornada, Steven G. Louie, Jeffrey B. Neaton We present an ab initio approach to investigate the interaction between single excitons and non-interacting biexcitons from first-principles using many-body perturbation theory within the GW approximation and the Bethe-Salpeter Equation approach. We apply our model to explore singlet-fission in acene molecular crystals. For these systems, we calculate the electronic coupling between singlet excitations and non-interacting but spin-correlated triplet pairs, explore the resulting singlet-fission rate, and associate the exciton-exciton coupling mechanism in terms of the crystal structure and given the nature and symmetry of the involved solid-state excitons. [Preview Abstract] |
Wednesday, March 15, 2017 9:24AM - 9:36AM |
K7.00006: Effects of molecular packing in organic crystals on singlet fission with ab initio many body perturbation theory Jonah Haber, Sivan Refaely-Abramson, Felipe H. da Jornada, Steven G. Louie, Jeffrey B. Neaton Multi-exciton generation processes, in which multiple charge carriers are generated from a single photon, are mechanisms of significant interest for achieving efficiencies beyond the Shockley-Queisser limit of conventional p-n junction solar cells. One well-studied multiexciton process is singlet fission, whereby a singlet decays into two spin-correlated triplet excitons. Here, we use a newly developed computational approach to calculate singlet-fission coupling terms and rates with an ab initio Green’s function formalism based on many-body perturbation theory (MBPT) within the GW approximation and the Bethe-Salpeter equation approach. We compare results for crystalline pentacene and TIPS-pentacene and explore the effect of molecular packing on the singlet fission mechanism. [Preview Abstract] |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K7.00007: Effect of co-crystallization on singlet fission efficiency in pentacene derivatives Xiaopeng Wang, Samuel Sanders, Luis Campos, Matthew Sfeir, Noa Marom Singlet fission (SF), the conversion of one singlet exciton into two triplet excitons, may lead to a twofold increase in the efficiency of organic photovoltaics. Since SF has been observed in crystalline pentacene, this material has drawn interest both experimentally and theoretically. Recently, it has been shown that SF efficiency in rubrene may be improved by modifying the crystal packing [CrystEngComm 18, 7353 (2016)]. Here, we study the effect of co-crystallization with small molecule H-bond donors on SF efficiency in pentacene derivatives. Five co-crystals are synthetized and their photoluminescence (PL) and absorption spectra are measured. First-principles calculations based on many-body perturbation theory (MBPT) are then employed to study their excitonic properties. By combining experiment and theory, we demonsrate that excitonic properties, including singlet-triplet gaps, exciton binding energies, and exciton localization, are significantly modulated in pentacene co-crystals. Consequently, co-crystallization becomes an effective strategy for improving SF efficiency in molecular crystals of organic semiconductors. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K7.00008: Dynamically Corrected Methods Can Explain Observed Discrepancies in Singlet Fission Properties of Quinoidal Bi- and Tetrathiophenes Mohammad R. Momeni Quinoidal bithiophene has been introduced (\textit{J. Phys. Chem. Lett.} \textbf{2015}, \textit{6}, 1375) as a very promising isolated compound for intramolecular singlet fission (iSF). In contrast, another study (\textit{J. Am. Chem. Soc.} \textbf{2015}, \textit{137}, 11294) revealed that quinoidal tetrathiophenes have no activity in the iSF process and are strong fluorophores instead. To address this unprecedented discrepancy quinoidal bithiophene and tetrathiophene compounds and their derivatives are carefully examined using the CASPT2 technique. Through comparison of the CASPT2 results with the CASSCF and RAS-2SF data, it is found that the dynamic electron correlation present in the CASPT2 method plays a crucial role for correct description of the multiexciton nature of the triplet pair $^{1}$[TT] state. Effects of substitution and structural modification on iSF activity of these compounds are also examined using the CASPT2 method where the obtained results are in accordance with previous experimental predictions. These results contribute to a better understanding of the iSF mechanism in quinoidal systems which could be relevant for designing new iSF active compounds. [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K7.00009: Quantitative prediction of optical absorption in molecular solids using an optimally tuned screened range-separated hybrid functional Arun K. Manna, Sivan Refaely-Abramson, Anthony Reilly, Alexandre Tkatchenko, Jeffrey B. Neaton, Leeor Kronik Quantitative prediction of optical absorption in the solid-state using density functional theory (DFT) is a long-standing challenge. In principle, this should be possible with time-dependent DFT (TDDFT). In practice, the results depend very strongly on the approximate exchange-correlation functional and standard approximations usually fail qualitatively in the solid state. We show that such prediction is possible, using the recently-developed time-dependent optimally-tuned screenedrange-separated hybrid (OT-SRSH). In this method the molecular electronic structure is determined by optimal tuning of the range-separation parameter in a range-separated hybrid functional. Screening and polarization in the solid-state are taken into account by adding long-range dielectric screening to the functional form. We provide a comprehensive benchmark for the accuracy of this approach, by considering the X23 benchmark set of molecular solids. The results are in good agreement with many-body perturbation theory in the GW-BSE approximation. We discuss strengths and weaknesses of the approach. We believe that it could be used for studies of molecular solids typically outside the reach of computationally more intensive methods. [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K7.00010: Electronic structure of PPP@ZnO from all-electron quasiarticle calculations Benjamin H\"{o}ffling, Dimitri Nabok, Claudia Draxl We investigate the electronic properties of poly(\emph{para}-phenylene) (PPP) adsorbed on the non-polar (001) surface of rocksalt (\emph{rs}) ZnO using all-electron density functional theory (DFT) as well as quasiparticle (QP) calculations within the \emph{GW} approach. A particular focus is put on the electronic band discontinuities at the interface, where we investigate the impact of quantum confinement, molecular polarization, and charge rearrangement. For our prototypical system, PPP@ZnO, we find a type-I heterostructure. Comparison of the band offsets derived from a QP-treatment of the hybrid system with predictions based on mesoscopic methods, like the Shockley-Anderson model or alignment via the electrostatic potential, reveals the inadequacy of these simple approaches for the prediction of the electronic structure of such inorganic/organic heterosystems. Finally, we explore the optical excitations of the interface compared to the features of the pristine components and discuss the methodological implications for the \emph{ab-initio} treatment of interface electronics. [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K7.00011: Application of ab initio many-body perturbation theory with Gaussian basis sets to the singlet and triplet excitations of organic molecules Samia Hamed, Tonatiuh Rangel, Fabien Bruneval, Jeffrey B. Neaton Quantitative understanding of charged and neutral excitations of organic molecules is critical in diverse areas of study that include astrophysics and the development of energy technologies that are clean and efficient. The recent use of local basis sets with ab initio many-body perturbation theory in the GW approximation and the Bethe-Saltpeter equation approach (BSE), methods traditionally applied to periodic condensed phases with a plane-wave basis, has opened the door to detailed study of such excitations for molecules, as well as accurate numerical benchmarks. Here, through a series of systematic benchmarks with a Gaussian basis, we report on the extent to which the predictive power and utility of this approach depend critically on interdependent underlying approximations and choices for molecules, including the mean-field starting point (eg optimally-tuned range separated hybrids, pure DFT functionals, and untuned hybrids), the GW scheme, and the Tamm Dancoff approximation. We demonstrate the effects of these choices in the context of Thiels' set while drawing analogies to linear-response time-dependent DFT and making comparisons to best theoretical estimates from higher-order wavefunction-based theories. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K7.00012: Efficient $G_0W_0$ using localized basis sets: a benchmark for molecules Petr Koval, Mathias Per Ljungberg, Daniel Sanchez-Portal Electronic structure calculations within Hedin's $GW$ approximation are becoming increasingly accessible to the community. In particular, as it has been shown earlier and we confirm by calculations using our \textbf{MBPT\_LCAO} package, the computational cost of the so-called $G_0W_0$ can be made comparable to the cost of a regular Hartree-Fock calculation. In this work, we study the performance of our new implementation of $G_0W_0$ to reproduce the ionization potentials of all 117 closed-shell molecules belonging to the G2/97 test set, using a pseudo-potential starting point provided by the popular density-functional package \textbf{SIESTA}. Moreover, the ionization potentials and electron affinities of a set of 24 acceptor molecules are compared to experiment and to reference all-electron calculations. [Preview Abstract] |
Wednesday, March 15, 2017 10:48AM - 11:00AM |
K7.00013: Benchmark of Ab Initio Bethe-Salpeter Equation Approach with Numeric Atom-Centered Orbitals Chi Liu, Jan Kloppenburg, Yosuke Kanai, Volker Blum The Bethe-Salpeter equation (BSE) approach based on the GW approximation has been shown to be successful for optical spectra prediction of solids and recently also for small molecules. We here present an all-electron implementation of the BSE using numeric atom-centered orbital (NAO) basis sets. In this work, we present benchmark of BSE implemented in FHI-aims for low-lying excitation energies for a set of small organic molecules, the well-known Thiel's set. The difference between our implementation (using an analytic continuation of the GW self-energy on the real axis) and the results generated by a fully frequency dependent GW treatment on the real axis is on the order of $\sim$0.07 eV for the benchmark molecular set. We study the convergence behavior to the complete basis set limit for excitation spectra, using a group of valence correlation consistent NAO basis sets (NAO-VCC-nZ), as well as for standard NAO basis sets for ground state DFT with extended augmentation functions (NAO+aug). The BSE results and convergence behavior are compared to linear-response time-dependent DFT, where excellent numerical convergence is shown for NAO+aug basis sets. [Preview Abstract] |
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