Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L1: Van der Waals Bonding in Advanced Materials IIFocus
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Sponsoring Units: DMP DCOMP Chair: Santosh KC, Oak Ridge National Laboratory Room: 260 |
Wednesday, March 15, 2017 11:15AM - 11:51AM |
L1.00001: Dabbling in the rich color palette of van der Waals bonded layered materials Invited Speaker: Alex Zettl The modest-strength van der Waals bond hits the sweet spot for facilitating the assembly of layered materials. I will discuss some recent experimental and theoretical explorations of van der Waals heterostructures, often with in-plane sp2-bonded components including boron nitride and graphene. The materials can themselves display novel physics and chemistry, or be used as aids for exploring the properties of complementary nanomaterials via electrical transport, optics, high resolution transmission electron microscopy, and scanning tunneling microscopy. [Preview Abstract] |
Wednesday, March 15, 2017 11:51AM - 12:03PM |
L1.00002: Strong van der Waals attractive forces in nanotechnology. Jeffrey Reimers The Dobson classification scheme for failure of London-like expressions for describing dispersion is reviewed. New ways to measure using STM data and calculate by first principles free energies of organic self-assembly processes from solution will be discussed, considering tetraalkylporphyrins on graphite. How strong van der Waals forces can compete against covalent bonding to produce new molecular isomers and reaction pathways will also be demonstrated, focusing on golds-sulfur bonds for sensors and stabilizing nanoparticles. .(1) Reimers, J. R.; Goerigk, L.; Ford, Elemans, J. A. A. W.; Hush, N. S.; Crossley, M. J. et al "A priori calculations of the free energy of formation from solution of polymorphic self-assembled monolayers" \textit{Proc. Natl. Acad. Sci. U.S.A.} \textbf{2015}, \textit{112}, E6101. (2) Reimers, J. R.; Ford, M. J.; Halder, A.; Ulstrup, J.; Hush, N. S. "Gold surfaces and nanoparticles are protected by Au(0)-thiyl species and are destroyed when Au(I)-thiolates form" \textit{Proc. Natl. Acad. Sci. U.S.A.} \textbf{2016}, \textit{113}, E1424 . (3) Reimers, J. R.; Li, M.; Wan, D.; Gould, T.; Ford, M. J. In \textit{Noncovalent interactions in quantum chemistry and physics: Theory and applications}; Otero de la Roza, A., DiLabio, G., Eds.; Elsevier: Amsterdam, 2017, p in press. [Preview Abstract] |
Wednesday, March 15, 2017 12:03PM - 12:15PM |
L1.00003: Modeling of Materials for Energy Storage: A Challenge for Density Functional Theory Merzuk Kaltak, Marivi Fernandez-Serra, Mark S. Hybertsen Hollandite $\alpha$-MnO$_2$ is a promising material for rechargeable batteries and is studied extensively in the community because of its interesting tunnel structure and the corresponding large capacity for lithium as well as sodium ions. However, the presence of partially reduced Mn ions due to doping with Ag or during lithiation makes hollandite a challenging system for density functional theory and the conventionally employed PBE+U method. A naive attempt to model the ternary system Li$_x$Ag$_y$MnO$_2$ with density functionals, similar to those employed for the case $y=0$, fails and predicts a strong monoclinic distortion of the experimentally observed tetragonal unit cell for Ag$_2$Mn$_8$O$_{16}$. Structure and binding energies are compared with experimental data and show the importance of van der Waals interactions as well as the necessity for an accurate description of the cooperative Jan-Teller effects for silver hollandite Ag$_y$MnO$_2$. Based on these observations a ternary phase diagram is calculated allowing to predict the physical and chemical properties of Li$_x$Ag$_y$MnO$_2$, such as stable stoichiometries, open circuit voltages, the formation of Ag metal and the structural change during lithiation. [Preview Abstract] |
Wednesday, March 15, 2017 12:15PM - 12:27PM |
L1.00004: Interplay of H$_{2}$O and K$^+$ inside the channels of Mn$_{8}$O$_{16}$ Vidushi Sharma, Merzuk Kaltak, Mark Hybertsen, Marivi Fernandez-Serra With the rapid growth in consumer electronics and electric vehicles, there is an increasing interest in developing high-density batteries, which requires investigation of robust electrode materials. One of these, $\alpha$-MnO$_{2}$, is inexpensive and environmentally benign to manufacture. It consists of an arrangement of corner- and edge- shared MnO$_{6}$ octahedra forming a $2 \times 2$ tunnel structure, and belongs to a family of ``octahedral molecular sieve structures" (OMS-$2$). Owing to the large tunnel cavity of OMS-$2$, cations such as K$^{+}$, Li$^{+}$, Ag$^{+}$, etc. as well as water molecules can be introduced into the $2\times2$ tunnel, thereby enabling us to tailor its chemical and physical properties. In this work, we focus on the incorporation of K${^+}$ in the tunnel, which stabilizes $\alpha$-MnO$_{2}$, in agreement with experiment. Our primary goal is to investigate the role of water in stabilizing the ions already present in a tunnel cavity, using first-principles density functional theory (DFT) calculations, including van der Waals interactions. We also analyze how the hydrogen-bond network competes with the ionic bonding of K$^+$ in the channel. [Preview Abstract] |
Wednesday, March 15, 2017 12:27PM - 12:39PM |
L1.00005: Thermo-mechanical behavior of nanoparticle membranes. Henry Chan, Badri Narayanan, Yifan Wang, Xiao-Min Lin, Heinrich Jaeger, Sankaranarayanan Subramanian Ultra-thin nanoparticle (NP) membranes are self-assembled hybrid materials that have attracted considerable interests. Monolayer membranes formed of simple dodecanethiol ligated gold NPs have mechanical strength that comes mostly from weak non-covalent van der Waals interactions between ligands, yet they can free-stand over micron-size holes and have a Young's modulus on the order of several GPa. We will present our recent experimental-theoretical study on the thermo-mechanical behavior of these membranes and reveal microscopic details relating to ligand rearrangement and dynamics that lead to their hysteretic mechanical response. The results provide insight that can be useful in the development of new non-covalent self-assembled materials with tunable properties. [Preview Abstract] |
Wednesday, March 15, 2017 12:39PM - 12:51PM |
L1.00006: Biogenic twinned crystals exhibiting unique morphological symmetry Anna Hirsch, Dvir Gur, Ben Palmer, Lia Addadi, Leslie Leiserowitz, Leeor Kronik Guanine crystals are widely used in nature as components of multilayer reflectors. Organisms control the size, morphology, and arrangement of these crystals, to obtain a variety of optical "devices" [1]. The reflection systems found in the lens of the scallop eye and in the copepod cuticle are unique in that the multilayered reflectors are tiled together to form a contiguous packed array. In the former, square crystals are tiled to form a reflecting mirror. In the latter, hexagonal crystals are closely packed to produce brilliant colors. Based on electron diffraction, morphology considerations, and density functional theory, these crystals were shown to possess similar monoclinic crystal symmetry, which we have previously identified as different from that of synthetic anhydrous guanine [2]. However, the crystals are different in that multiple twinning about the \{012\} and the \{011\} crystallographic planes results in square and hexagonal morphology, respectively. This is a unique example where controlled twinning is used as a strategy to form a morphology with higher symmetry than that of the underlying crystal, allowing for tilling that facilitates optical functionality. [1] Gur et al., Adv. Mat. (2016) [2] Hirsch et al., Chem. Mat. 27, 8289 (2015) [Preview Abstract] |
Wednesday, March 15, 2017 12:51PM - 1:03PM |
L1.00007: Origin and structure of polar domains in doped molecular crystals Ido Azuri, Elena Meirzadeh, Yubo Qi, David Ehre, Andrew Rappe, Meir Lahav, Leeor Kronik, Igor Lubomirsky Doping is a primary tool for the modification of the properties of materials. Occlusion of guest molecules in crystals generally reduces their symmetry by the creation of polar domains, which engender polarization and pyroelectricity in the doped crystals. Here we describe a molecular-level determination of the structure of such polar domains, as created by low dopant concentrations ($<$0.5\%). The approach comprises crystal engineering and pyroelectric measurements, together with dispersion-corrected density functional theory and classical molecular dynamics calculations of the doped crystals, using neutron diffraction data of the host at different temperatures. This approach is illustrated using centrosymmetric $\alpha$-glycine crystals doped with minute amounts of different L-amino acids. The experimentally determined pyroelectric coefficients are explained by the structure and polarization calculations, thus providing strong support for the local and global understanding of how different dopants influence the properties of molecular crystals. [Preview Abstract] |
Wednesday, March 15, 2017 1:03PM - 1:15PM |
L1.00008: Anharmonic and Quantum Fluctuations in Molecular Crystals from Ab Initio Simulations Mariana Rossi, Piero Gasparotto, Michele Ceriotti Molecular crystals often exist in multiple competing polymorphs which are challenging to be predicted computationally, but show significantly different physicochemical properties. This challenge is not due only to the combinatorial search space, but also to the complex interplay of subtle effects determine the relative stability of different structures. Here we estimate all contributions to the free energies of these systems with density-functional theory, including the oft-neglected anharmonic contributions and nuclear quantum effects, by using a series of different flavors of thermodynamic integration. As an example, for the two most stable forms of paracetamol we find that anharmonic contributions, different descriptions of van der Waals interactions, and nuclear quantum effects {\bf all} matter to quantitatively determine the stability of different phases [1]. Our studies indicate that anharmonic free energies could play an important role for molecular crystals composed by large molecules and opens the way for a systematic inclusion of these effects in order to obtain a predictive screening of structures. [1] Rossi, Gasparotto, Ceriotti, {\it Phys. Rev. Lett.} {\bf 117}, 115702 (2016). [Preview Abstract] |
Wednesday, March 15, 2017 1:15PM - 1:27PM |
L1.00009: First-Principles Molecular Crystal Structure Prediction: The Importance of Collective van der Waals Interactions and Free Energies Johannes Hoja, Hsin-Yu Ko, Roberto Car, Robert A. DiStasio Jr., Alexandre Tkatchenko For meaningful crystal structure predictions (CSP) of practically relevant molecular crystals, it is imperative to calculate relative lattice energies with an accuracy of about 1 kJ/mol since it is necessary to correctly rank the stabilities of numerous low-energy polymorphs. Accurate results can be obtained by utilizing density-functional theory (DFT) supplemented by a high-level van der Waals (vdW) model, such as the many-body dispersion (MBD) method. Since relative stabilities have to be determined at finite temperatures, vibrational free energies have to be considered as well. The importance of an accurate treatment of vdW interactions and free energies is discussed in terms of the systems studied in the most recent CSP blind test [Reilly et al., Acta Cryst. B72, 439 (2016)], with a particular focus on a challenging case of a highly polymorphic system. It is shown that collective many-body vdW interactions completely change the relative stabilities of the studied polymorphs in comparison to a pairwise approach. Furthermore, the inclusion of thermal fluctuations also leads to a significant improvement of the relative stabilities. Overall, the CSP approach based on DFT+MBD provides remarkably accurate structures and stability rankings for relevant molecular crystals. [Preview Abstract] |
Wednesday, March 15, 2017 1:27PM - 1:39PM |
L1.00010: Genarris: Parallelized Configuration Space Screening of Molecular Crystals Aided by a Harris Approximation Xiayue Li, Farren Curtis, Christoph Schober, Alvaro Vazquez-Mayagoitia, Harald Oberhofer, Noa Marom Genarris is a Python-based package for parallelized configuration space screening for crystals of rigid molecules. Genarris is designed to rapidly create a low-energy and high-diversity initial pool for further crystal structure prediction based on a genetic algorithm. Genarris generates random structures with physical constraints by applying space group symmetries and customizable closeness checks. For fast total energy evaluations, Genarris employs a Harris approximation, whereby the total charge density of a molecular crystal is constructed via superposition of single molecule densities. Dispersion-corrected density functional theory (DFT) is then used with the Harris density as input to compute the total energy in one iteration. To balance the need for quality and diversity, the pool is enriched with structures only meeting looser closeness criteria. The lowest energy structures are then selected from clusters of similar structures, found by a $k-$means algorithm based on a radial distribution function descriptor. [Preview Abstract] |
Wednesday, March 15, 2017 1:39PM - 1:51PM |
L1.00011: Effect of packing motifs on the energy ranking and electronic properties of putative crystal structures of tricyano-1,4-dithiino[c ]-isothiazole Farren Curtis, Xiaopeng Wang, Noa Marom We present an analysis of putative structures of tricyano-1,4-dithiino[c]- isothiazole (TCS3), generated within the sixth crystal structure prediction blind test. Typical packing motifs are identified and characterized in terms of distinct patterns of close contacts and regions of electrostatic and dispersion interactions. We find that different dispersion-inclusive density functional theory (DFT) methods systematically favor specific packing motifs, which may affect the outcome of crystal structure prediction efforts. The effect of crystal packing on the electronic and optical properties of TCS3 is investigated using many-body perturbation theory within the GW approximation and the Bethe--Salpeter equation (BSE). We find that a structure with Pna2$_{\mathrm{1\thinspace }}$symmetry and a bilayer packing motif exhibits intermolecular bonding patterns reminiscent of pi--pi stacking and has markedly different electronic and optical properties than the experimentally observed P2$_{\mathrm{1}}$/n structure with a cyclic dimer motif, including a narrower band gap, enhanced band dispersion, and broader optical absorption. The Pna2$_{\mathrm{1\thinspace }}$bilayer structure is close in energy to the observed structure and may be feasible to grow. [Preview Abstract] |
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