Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session F6: Focus Session: Van der Waals Bonding in Advanced Materials - Functional Materials |
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Sponsoring Units: DMP Chair: Per Hyldgaard, Chalmers University of Technology Room: 302 |
Tuesday, March 19, 2013 8:00AM - 8:12AM |
F6.00001: Active Pharmaceutical Ingredients: Prediction of Physical-Chemical Properties from First Principles Loredana Valenzano Polymorphism in active pharmaceutical ingredients (APIs) plays a crucial role both for medical and intellectual property concerns but despite ongoing efforts, experimental and computational investigations of the existence and the physical-chemical properties of the same compound in different forms is still an open question.While comparison between computed and experimental values for properties derived from differences between states is often promising (such as bulk modulus), results are disappointing for absolute values (such as density). Quantum mechanical computational methods describe the systems at 0K, experimentally properties are often evaluated at room temperature. Therefore it is not surprising that results determined from first principles dramatically differ from those obtained experimentally. By applying a quantum mechanical periodic approach that takes into account long range London dispersion forces fitted for solid materials, and by imposing different cell volumes corresponding to different thermodynamic conditions, we show how results from calculations at 0K (structures, vibrational spectra, elastic constants) may be compared to experimental values at higher temperatures, helping to foster a stronger linkage between computational and experimental work on systems such as APIs. Where experimental results are not available, our work represents an innovative approach in addressing the properties of APIs. Our results can also serve as foundation for the developing of new force fields to be adopted within a multi-scale computational approach. [Preview Abstract] |
Tuesday, March 19, 2013 8:12AM - 8:24AM |
F6.00002: Many-Body van der Waals Effects in Advanced Materials Alexandre Tkatchenko, Anatole von Lilienfeld, Robert A. DiStasio Jr. Van der Waals (vdW) interactions are ubiquitous in molecules and condensed matter. These interactions are inherently quantum mechanical phenomena that arise from concerted correlations between many electrons within a given molecular system. Despite this fact, the vast majority of theoretical calculations include long-range vdW interactions based on a simple effective interatomic pairwise model. We introduce an efficient method that accurately describes the full long-range many-body vdW energy [1,2], and demonstrate that many-body contributions can significantly exceed the highly coveted ``chemical accuracy''. Cases studied include intermolecular binding energies, the conformational hierarchy of DNA structures [2], the geometry and stability of molecular crystals [1], and supramolecular host--guest complexes [3]. Our findings suggest that inclusion of the many-body vdW energy is essential for achieving chemical accuracy and therefore must be accounted for when studying advanced materials. [1] Tkatchenko, DiStasio, Car, Scheffler, PRL (2012), [2] DiStasio, von Lilienfeld, Tkatchenko, PNAS (2012), [3] Tkatchenko, Alfe, Kim, JCTC (2012). [Preview Abstract] |
Tuesday, March 19, 2013 8:24AM - 8:36AM |
F6.00003: First-Principles Calculations of the Role of PVP in the Controlled Synthesis of Au Nanostructures Shih-Hsien Liu, Wissam Al-Saidi, Kristen Fichthorn Structure-directing agents such as PVP play an important role in determining the shape of metal nanostructures in solution-phase syntheses. It is usually hypothesized that structure-directing molecules bind more strongly to certain crystal facets, which grow at the expense of facets on which they are less strongly bound. In this study, we use dispersion-corrected density functional theory to resolve the role of PVP in the shape-selective synthesis of Au nanostructures. We calculate binding energies for the 2-pyrrolidone ring of PVP on Au(111), (5 $\times$ 1) Au(100)-hex, and Au(100) slabs in vacuum. The results show that there is no significant difference between the binding of 2-pyrrolidone to Au(111) and Au(100)-hex, while 2-pyrrolidone binds more strongly to Au(111) than to Au(100). We discuss the origins of these trends. Our results are consistent with experiments, in which (111)-faceted Au nanostructures are formed with the assistance of PVP. [Preview Abstract] |
Tuesday, March 19, 2013 8:36AM - 8:48AM |
F6.00004: van der Waals Density Functional Studies of Gas Binding and Transport in Zeolitic Imidazolate Frameworks Keith Ray, David Olmsted, Ning He, Yao Houndonougbo, Brian Laird, Mark Asta Gas adsorption selectivity and transport barriers in a series of Zeolitic Imidazolate Frameworks (ZIFs) are calculated with the van der Waals density functional [1]. In these microporous materials, promising for natural gas upgrading applications, CO2 molecules are found to preferentially adsorb [2] when compared with CH4 depending on the ZIF chemical functionalization. The role of the interaction between the CO2 quadrupole and the host framework, as well as the significant dispersion contribution to both CO2 and CH4 binding are discussed. Diffusion barriers are calculated with the nudged elastic band method (NEB) and results are found to depend on the inclusion of the van der Waals energy.\\[4pt] [1] M. Dion, H. Rydberg, E. Schroder, D. C. Langreth, B. I. Lundqvist, Phys. Rev. Let. 92, 246401 (2004)\\[0pt] [2] K. G. Ray, D. Olmsted, N. He, Y. Houndonougbo, B.B. Laird, M. Asta, Phys. Rev. B 85, 085410 (2012). [Preview Abstract] |
Tuesday, March 19, 2013 8:48AM - 9:00AM |
F6.00005: Self-assembly of functionalized anthradithiophene on Au(111) Brad Conrad, Shawn Huston, Jiuyang Wang, Marsha Loth, John Anthony, Daniel Dougherty We utilize scanning tunneling microscopy (STM) to characterize the initial growth and crystallization of the high-performance, small organic molecule 2,8-difluoro-5,11-triethylsilylethynyl (diF TESADT) on Au(111). Two ordered structures are observed with diF TESADT backbone planes parallel to the substrate. Submolecular resolution imaging of the first monolayer ordered film regions realizes structures with close approach of fluorine-sulfur and fluorine-fluorine atoms of alternating molecules. These measurements provide evidence for the importance of non-covalent F-S and F-F interactions in driving 2D self-assembly. Scanning Tunneling Spectroscopy indicates a 2.4 eV transport gap which is insensitive to the local domain. Structures and growth are put in context of bulk measurements and device performance measurements. [Preview Abstract] |
Tuesday, March 19, 2013 9:00AM - 9:12AM |
F6.00006: Using NMR to study small molecule adsorption in metal organic frameworks M.G. Lopez, P. Canepa, T. Thonhauser We calculate the carbon nuclear magnetic resonance (NMR) chemical shift for the CO$_2$ molecule and the hydrogen shift for both H$_2$ and H$_2$O inside the metal organic framework structure Mg-MOF74 using \emph{ab initio} calculations at the density functional theory level\footnote{T. Thonhauser et al., J. Chem. Phys. \textbf{131}, 101101 (2009).}$^,$\footnote{C. J. Pickard and F. Mauri, Phys. Rev. B {\bf 63}, 245101 (2001).} with the van der Waals density functional (vdW-DF).\footnote{M. Dion et al., Phys. Rev. Lett. \textbf{92}, 246401 (2004).} These shifts are obtained while placing the small molecules throughout the structure, including the calculated adsorption site for various loading scenarios. Our binding energy results agree well with previous experiments and calculation, and the NMR calculations show that it is reasonable to expect an experimentally observable change in the chemical shift depending on adsorbant, position, and loading. By providing this mapping of chemical shift to position and loading for these adsorbants, we argue that NMR probes could be used to provide information about the position at which these small molecules bind within the MOF and provide information about the loading of the adsorbed molecule. [Preview Abstract] |
Tuesday, March 19, 2013 9:12AM - 9:48AM |
F6.00007: Spectroscopic studies of van der Waals bonding and interactions in microporous materials Invited Speaker: Yves Chabal Van der Waals interactions govern the interaction of gas phase molecules in microporous materials. New theoretical approaches, such as DF-vdW methods, have brought great insight into the results of vdW forces on the adsorption and diffusion properties of molecular guests. In this talk, we highlight the role of vibrational spectroscopies (infrared and Raman) in providing information that can directly test such theoretical approaches. Typically, vdW interactions lead to measurable shifts in molecular internal modes, which can be calculated. We also show that vdW interactions often lead to minor structural alteration or reconfiguration of the microporous hosts, which can clearly be observed by IR or Raman spectroscopy. Examples will be taken from molecular hydrogen storage and gas phase separation in Metal Organic Framework materials, which represent a versatile class of porous materials. For example, the origin of interesting ``gate opening'' phenomena in flexible MOFs, leading to highly selective adsorption, will be described. [Preview Abstract] |
Tuesday, March 19, 2013 9:48AM - 10:00AM |
F6.00008: Van der Waals density functional study of water binding in metal-organic frameworks Kyuho Lee, Berend Smit, Jeffrey B. Neaton Metal-organic frameworks (MOFs) are promising candidate materials for gas storage, gas separation and catalysis. However, MOFs are vulnerable to humid air and effective surface area drops dramatically on an exposure to water [1]. In this theoretical study, we investigate the interaction of single water molecule with MOF-74 on different binding sites by using van der Waals density functionals. We also explore how different type of metal cations affect the interaction.\\[4pt] [1] S. S. Kaye, A. Daily, O. M. Yaghi and J. R. Long, J. Am. Chem. Soc. \textbf{129}, 14176 (2007). [Preview Abstract] |
Tuesday, March 19, 2013 10:00AM - 10:12AM |
F6.00009: Understanding CO$_{2}$/N$_{2}$ Selectivity and Binding in MOFs Using Dispersion-Corrected DFT Joshua Howe, Kyuho Lee, Berend Smit, Jeffrey Neaton Metal-organic frameworks (MOFs) are a class of highly ordered, highly customizable nanoporous materials that are attractive for use in energy-relevant gas separations. MOF-253 (AlOH)(bpydc) can be post-synthetically modified by introduction of metal cations and charge-stabilizing anions [1]. Post-synthetically modified MOF-253 samples have been shown to exhibit enhanced CO$_{2}$/N$_{2}$ selectivity over the unmodified framework [1]. Here we focus on the following series of post-synthetic modifications: ~CoCl$_{2}$, CuCl$_{2}$, FeCl$_{2}$, NiCl$_{2}$, PdCl$_{2}$. We use the vdW-DF, vdW-DF2, and DFT-D2 dispersion-corrected density functional theory (DFT) methods to study CO$_{2}$ and N$_{2}$ binding trends in this series of modified frameworks. Particular focus is paid to examining the predictive power of our calculations on both the modified framework and modified bipyridine clusters as a proxy for the full framework. Additionally, we examine the suitability of an approximate Henry coefficient model to predict measured gas selectivity trends [1]. \\[4pt] [1] E. Bloch, et. al, J. Am. Chem. Soc., 132, 14382-14384, 2010. [Preview Abstract] |
Tuesday, March 19, 2013 10:12AM - 10:48AM |
F6.00010: The Role of Many-Body Dispersion Interactions in Molecular Crystals Invited Speaker: Noa Marom The structure, energetics, and electronic properties of molecular crystals are studied using density functional theory (DFT) with the recently developed many-body dispersion (MBD) method [Tkatchenko et al. Phys. Rev. Lett. 108, 236402 (2012)]. It is shown that accounting for the long-range electrostatic screening in extended systems is essential for obtaining the correct dielectric constants and ensuing optical properties of molecular crystals [Schatschneider et al., arXiv:1211.1683]. Furthermore, accounting for the non-additive many-center dispersion interactions is crucial for obtaining a highly accurate description of the energetics of molecular crystals. This includes lattice energies, sublimation enthalpies [Reilly et al., to be published], and relative stabilities of polymorphs [Marom et al. arXiv: 1210.5636] \\[4pt] In collaboration with Leslie Leiserowitz, Weizmann Institute of Science, Israel; Bohdan Schatschneider, The Pennsylvania State University, Fayette; Robert DiStasio, Princeton University; Anthony Reilly and Guo-Xu Zhang, Fritz Haber Institute of the Max Planck Society, Berlin; James Chelikowsky, The University of Texas at Austin; and Alexandre Tkatchenko, Fritz Haber Institute of the Max Planck Society, Berlin. [Preview Abstract] |
Tuesday, March 19, 2013 10:48AM - 11:00AM |
F6.00011: Stiffness of Diphenylalanine-Based Molecular Solids from First Principles Calculations Ido Azuri, Oded Hod, Ehud Gazit, Leeor Kronik Diphenylalanine-based peptide nanotubes were found to be unexpectedly stiff, with a Young modulus of 19 GPa. Here, we calculate the Young modulus from first principles, using density functional theory with dispersive corrections. This allows us to show that at least half of the stiffness of the material comes from dispersive interactions and to identify the nature of the interactions that contribute most to the stiffness. This presents a general strategy for the analysis of bioinspired functional materials. [Preview Abstract] |
Tuesday, March 19, 2013 11:00AM - 11:12AM |
F6.00012: Molecular Transport in Metal Organic Framework Ma- terials P. Canepa, N. Nijem, Y.J. Chabal, T. Thonhauser Metal organic frameworks (MOF) materials are a class of porous materials well suited for hydrogen storage and gas separation. While current work on MOFs focuses mostly on the adsorption properties of small molecules, their diffusion is still poorly understood. To elucidate the diffusion process, we study the diffusion of H$_2$, CO$_2$, and H$_2$O in the nano-pores of MOF-74-Mg by combining \emph{ab initio} simulations with infrared (IR) spectroscopy. We present computed adsorption energies and changes in the IR frequencies upon adsorption. We also discuss several diffusion mechanisms and their calculated barriers. We further verify the existence of the debated secondary binding sites for guest molecules and we discuss the role played by H$_2$O. We find that H$_2$O is much more likely to adsorb in the MOF than H$_2$ and CO$_2$, leading to a significant reduction of the adsorption capabilities of the MOF towards these target molecules, and hence resulting in limitations for practical applications. Overall, our computational findings are in very good agreement with experiment and they provide a fundamental understanding of the diffusion processes of small molecules in these nano-porous materials, with implication for the usability of MOFs in gas separation and storage applications. [Preview Abstract] |
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