Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session L31: Advances in Density Functional Theory VIFocus

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Sponsoring Units: DCP Chair: Marivi Fernandez Serra, SUNYStony Brook Room: 331 
Wednesday, March 16, 2016 11:15AM  11:51AM 
L31.00001: Fast RPA and GW calculations: cubic system size scaling Invited Speaker: Georg Kresse The random phase approximation (RPA) to the correlation energy and the related GW approximation are among the most promising methods to obtain accurate correlation energy differences and QP energies from diagrammatic perturbation theory at reasonable computational cost. The calculations are, however, usually one to two orders of magnitude more demanding than conventional density functional theory calculations. Here, we show that a cubic system size scaling can be readily obtained reducing the computation time by one to two orders of magnitude for large systems. Furthermore, the scaling with respect to the number of k points used to sample the Brillouin zone can be reduced to linear order. In combination, this allows accurate and very wellconverged singlepoint RPA and GW calculations, with a time complexity that is roughly on par or better than for selfconsistent HartreeFock and hybridfunctional calculations [12]. Furthermore, the talk discusses the relation between the RPA correlation energy and the GW approximation: the selfenergy is the derivative of the RPA correlation energy with respect to the Green's function. The calculated selfenergy can be used to compute QPenergies in the GW approximation, any first derivative of the total energy, as well as corrections to the correlation energy from the changes of the charge density when switching from DFT to a manybody body description (GW singles energy contribution) [3]. [1] Merzuk Kaltak, Ji\v{r}\'{\i} Klime\v{s}, and Georg Kresse, J. Chem. Theory Comput., 10, 24982507 (2014). \newline [2] Merzuk Kaltak, Ji\v{r}\'{\i} Klime\v{s}, and Georg Kresse, Phys. Rev. B 90, 054115 (2014). \newline [3] Ji\v{r}\'{\i} Klime\v{s}, M. Kaltak, E. Maggio, and G.~ Kresse,~ J. Chem. Phys. 140, 084502 (2015). [Preview Abstract] 
Wednesday, March 16, 2016 11:51AM  12:03PM 
L31.00002: Influence of {\it xc} functional on thermalelastic properties of Ceria: A DFTbased DebyeGr{\"u}neisen model approach JiHwan Lee, Youngjoo Tak, Taehun Lee, Aloysius Soon Ceria (CeO$_{2x}$) is widely studied as a choice electrolyte material for intermediatetemperature ($\sim800$\,K) solid oxide fuel cells. At this temperature, maintaining its chemical stability and thermalmechanical integrity of this oxide are of utmost importance. To understand their thermalelastic properties, we firstly test the influence of various approximations to the densityfunctional theory (DFT) $xc$ functionals on specific thermalelastic properties of both CeO$_2$ and Ce$_2$O$_3$. Namely, we consider the localdensity approximation (LDA), the generalized gradient approximation (GGAPBE) with and without additional Hubbard $U$ as applied to the $4f$ electron of Ce, as well as the recently popularized hybrid functional due to HeydScuseriaErnzehof (HSE06). Next, we then couple this to a volumedependent DebyeGr{\"u}neisen model to determine the thermodynamic quantities of ceria at arbitrary temperatures. We find an explicit description of the strong correlation (e.g. via the DFT$+U$ and hybrid functional approach) is necessary to have a good agreement with experimental values, in contrast to the meanfield treatment in standard xc approximations (such as LDA or GGAPBE). [Preview Abstract] 
Wednesday, March 16, 2016 12:03PM  12:15PM 
L31.00003: Catalytic Effects of Oxide Surfaces on DielsAlder Cycloaddition between Furan and Methyl Acrylate: A DFT Study. Taha Salavatifard, Glen Jenness, Stavros Caratzoulas, Douglas Doren Using density functional theory with periodic boundary conditions, we study the catalytic effects of oxide surfaces such as ZrO\textunderscore 2 and HfO\textunderscore 2 on DielsAlder reaction between furan and methyl acrylate. The cycloadduct can be dehydrated later to produce methyl benzoic which is an important step toward benzoic acid production. The gasphase and onsurface reaction mechanisms are studied in detail. The surface hydration effects on the reaction mechanism and energy profile are studied as well. Our calculations show that the oxide surfaces catalyze the reaction significantly through the interaction of metal sites with methyl acrylate. The calculations are interpreted by making use of electronic density of states and band structure of the catalyst. [Preview Abstract] 
Wednesday, March 16, 2016 12:15PM  12:27PM 
L31.00004: Role of Exchange and Correlation in Predicting Structures and Properties of Fluoride Materials Nenian Charles, James Rondinelli The study of fluorinebased inorganic compounds has captured the attention of condensed matter physicists as a route to engineer novel states of matter. Here, we present a density functional theory (DFT) study on fluorides with structures ranging from simple to complex, including KF (rock salt), MnF$_2$ and VF$_2$ (rutile), KMnF$_3$ (perovskite), and Na$_3$MnF$_6$ and Na$_6$ScF$_6$ (cryolite). % The focus is on understanding the accuracy of various exchangecorrelation functionals for the prediction of structural, electronic, and phonon properties at four different levels of theory, i.e., the local density approximation (LDA), generalized gradient approximation (GGA), metaGGA, and hybrid functional level with exact exchange. % Specifically, we draw attention to the metaGGA functional MS2 [Sun \emph{et al}, Phys.\ Rev.\ Lett., \textbf{111}, 106401 (2013)], demonstrating that although it shows improvements over the LDA and GGA functionals in predicting structural properties of fluorides, %,\emph{i.e.} volume errors $\leq2\%$, MS2 generally performs poorer for the electronic and phonon properties. % Our study provides useful insights for predictive design of functional halide compounds using computational models based on DFT. [Preview Abstract] 
Wednesday, March 16, 2016 12:27PM  12:39PM 
L31.00005: Bond Breaking in Epoxy Systems: A Combined QM/MM Approach Stephen Barr, Gary Kedziora, Allison Ecker, James Moller, Rajiv Berry, Tim Breitzman A novel method to combine molecular mechanics and quantum mechanics (QM/MM) is developed with the intent to accurately and efficiently account for covalent bond breaking in polymer systems. Since classical force fields cannot accurately account for bond breaking, and QM is too demanding to simulate large systems, a hybrid approach is required. In the method demonstrated here, strain is applied to the system using a classical force field. When a bond break is likely, a zone surrounding the bond is used in a QM calculation to determine which, if any, bonds break. The QM result is then used to reconstitute the system to continue the classical simulation until another QM calculation is triggered. In this way a QM calculation is only computed when and where it is needed, allowing for an efficient simulation. A key component of this method is a density functional theory (DFT) method which provides accurate forces as bonds are pulled past their breaking points. To find the best method, a number functionals are compared with high level QM calculations by pulling various small molecules, representative of epoxies, past a bond breaking event. Appropriate values for the QM zone size and the QM trigger criteria are also determined. The overall QM/MM method is then applied to an epoxy system. [Preview Abstract] 
Wednesday, March 16, 2016 12:39PM  1:15PM 
L31.00006: Bayesian Error Estimation Functionals Invited Speaker: Karsten W. Jacobsen The challenge of approximating the exchangecorrelation functional in Density Functional Theory (DFT) has led to the development of numerous different approximations of varying accuracy on different calculated properties. There is therefore a need for reliable estimation of prediction errors within the different approximation schemes to DFT. The Bayesian Error Estimation Functionals (BEEF) have been developed with this in mind. The functionals are constructed by fitting to experimental and highquality computational databases for molecules and solids including chemisorption and van der Waals systems. This leads to reasonably accurate generalpurpose functionals with particual focus on surface science. The fitting procedure involves considerations on how to combine different types of data, and applies Tikhonov regularization and bootstrap cross validation. The methodology has been applied to construct GGA and metaGGA functionals with and without inclusion of longranged van der Waals contributions. The error estimation is made possible by the generation of not only a single functional but through the construction of a probability distribution of functionals represented by a functional ensemble. The use of the functional ensemble is illustrated on compound heat of formation and by investigations of the reliability of calculated catalytic ammonia synthesis rates. [Preview Abstract] 
Wednesday, March 16, 2016 1:15PM  1:27PM 
L31.00007: Joint Density Functional Theory for the electrode/electrolyte interface: Benchmarking liquid structure with experiment and {\it ab initio} molecular dynamics Kendra LetchworthWeaver, Christine Umbright, Maria Chan, Paul Fenter, T. A. Arias Understanding the physics of the interface between a charged electrode surface and a fluid electrolyte would inform design of electrochemical energy storage and conversion devices. However, such studies require a simultaneously accurate yet inherently multiscale theory. Joint densityfunctional theory (JDFT) bridges the relevant lengthscales by joining a fully {\it ab initio} description of the electrode with a low computational cost, yet atomically detailed classical DFT description of the liquid electrolyte structure. Leveraging JDFT within our framework to treat charged systems in periodic boundary conditions, we can predict the voltagedependent structure and energetics of solvated ions at the interface between graphitic and singlecrystalline metallic electrodes and technologically relevant liquid electrolytes. First, we elucidate the physical origin of the experimentally measured voltagedependent differential capacitance of an Ag(111) electrode in aqueous NaF electrolyte, examining the crucial role of ion desolvation and physisorption onto the electrode surface. We go on to compare the JDFTpredicted interfacial liquid structure next to a graphitic electrode with results obtained from Xray reflectivity measurements and {\it ab initio} molecular dynamics simulations. [Preview Abstract] 
Wednesday, March 16, 2016 1:27PM  1:39PM 
L31.00008: Role of Van der Waals interactions in determining the structure of liquid tellurides Matthieu Micoulaut, Hugo FloresRuiz, Vanessa Coulet, Andrea Piarristeguy, Mark Johnson, Gabriel Cuello, Annie Pradel The simulation of tellurides using standard density functional (DFT) theory based molecular dynamics usually leads to an overestimation of the bond distances and a noticeable mismatch between theory and experiments when e.g. structure functions are being directly compared. Here, the structural properties of several compositions of GeTe and GeSbTe liquids are studied from a combination of neutron diffraction and DFTbased molecular dynamics. Importantly, we find an excellent agreement in the reproduction of the structure in real and reciprocal spaces, resulting from the incorporation of dispersion forces in the simulation. We then investigate structural properties including structure factors, pair distribution functions, angular distributions, coordination numbers, neighbor distributions, and compare our results with experimental findings. \par {\bf References:}\par Physical Review B 92, 134205 (2015)\par Physical Review B 89, 174205 (2014)\par Physical Review B 90, 094207 (2014)\par [Preview Abstract] 
Wednesday, March 16, 2016 1:39PM  1:51PM 
L31.00009: Ti $\alpha  \omega$ phase transformation and metastable structure, revealed by the solidstate nudged elastic band method Nikolai Zarkevich, Duane D. Johnson$^{2,}$ Titanium is on of the four most utilized structural metals, and, hence, its structural changes and potential metastable phases under stress are of considerable importance. Using DFT+U combined with the generalized solidstate nudged elastic band (SSNEB) method, we consider the pressuredriven transformation between Ti $\alpha$ and $\omega$ phases, and find an intermediate metastable bodycentered orthorhombic (bco) structure of lower density. We verify its stability, assess the phonons and electronic structure, and compare computational results to experiment. Interestingly, standard density functional theory (DFT) yields the $\omega$ phase as the Ti ground state, in contradiction to the observed $\alpha$ phase at low pressure and temperature. We correct this by proper consideration of the strongly correlated $d$electrons, and utilize DFT+U method in the SSNEB to obtain the relevant transformation pathway and structures. [Preview Abstract] 
Wednesday, March 16, 2016 1:51PM  2:03PM 
L31.00010: The effect of the pair correlation function on dynamic density functional theory Stephen J. Tate, Benjamin D. Goddard, Grigorios A. Pavliotis, Serafim Kalliadasis In a previous study [1], a general dynamical density functional theory (DDFT) to include hydrodynamic interactions (HI) and inertial effects of colloidal particles was derived and validated with stochastic simulations. But the pair correlation function, g, was approximated with a simplest possible volumeexclusion function, namely a Heaviside step function. Here we explore what effect more accurate g's have on the same DDFT. These include a correction giving the PercusYevick solution for hard spheres, which is known analytically. Furthermore, since we typically deal with systems outside of equilibrium, we model nonadiabatic effects to the HI terms in the DDFT, including density and momentum dependence. [1] B.D. Goddard, A. Nold, N. Savva, G.A. Paviotis and S. Kalliadasis, "General dynamical density functional theory for classical fluids," Phys. Rev. Let.. 109 (120603) 2012. [Preview Abstract] 
Wednesday, March 16, 2016 2:03PM  2:15PM 
L31.00011: Understanding the spurious DFT fractional charge in the electrochemical double layer Leanne Chen, Michal Bajdich, Alan Luntz, Karen Chan, Jens Norskov An ongoing challenge in computational electrochemistry is the accurate determination of electrochemical barriers at constant electrode potential. Recently, our group developed an efficient scheme to determine the barriers using a simple extrapolation based on the interfacial charge [1]. However, semilocal DFT calculations have shown that the magnitude of the charge of solvated species (H$_{\mathrm{3}}$O$^{\mathrm{+}}$, OH$^{\mathrm{}}$, Li$^{\mathrm{+}}$, Na$^{\mathrm{+}})$ in the outer Helmholtz plane is not 1e, but always near 0.6e, which suggests a charge delocalization error in DFT. Furthermore, we frequently observe inaccurate alignment of the metal Fermi and solvent energy levels. Using an increasing amount of exact exchange, we first analyze the charge delocalization error in the dissociation of NaCl molecule, where a large amount of exchange is need to reproduce the steplike transition of charge from $+$1 to 0 on the dissociated Na and Cl. Next, we apply the same method to the metalwater interface with solvated ions at varying distances from the surface. The performance of hybrid and other fractional chargecorrected functionals will be discussed together with the possibility of a simple correction scheme. [1] Chan, K.; N{\o}rskov, J. K. Electrochemical Barriers Made Simple. \textit{J. Phys. Chem. Lett.} \textbf{2015}, \textit{6} (14), 26632668. [Preview Abstract] 
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