Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session A31: Advances in Density Functional Theory IFocus

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Sponsoring Units: DCP Chair: Donald Truhlar, University of Minnesot Room: 331 
Monday, March 14, 2016 8:00AM  8:36AM 
A31.00001: \textbf{SCAN: An Efficient Density Functional Yielding Accurate Structures and Energies of DiverselyBonded Materials} Invited Speaker: Jianwei Sun The accuracy and computational efficiency of the widely used KohnSham density functional theory (DFT) are limited by the approximation to its exchangecorrelation energy E$_{\mathrm{xc}}$. The earliest local density approximation (LDA) overestimates the strengths of all bonds near equilibrium (even the vdW bonds). By adding the electron density gradient to model E$_{\mathrm{xc}}$, generalized gradient approximations (GGAs) generally soften the bonds to give robust and overall more accurate descriptions, except for the vdW interaction which is largely lost. Further improvement for covalent, ionic, and hydrogen bonds can be obtained by the computationally more expensive hybrid GGAs, which mix GGAs with the nonlocal exact exchange. MetaGGAs are still semilocal in computation and thus efficient. Compared to GGAs, they add the kinetic energy density that enables them to recognize and accordingly treat different bonds, which no LDA or GGA can [1]. We show here that the recently developed nonempirical strongly constrained and appropriately normed (SCAN) metaGGA [2] improves significantly over LDA and the standard PerdewBurkeErnzerhof GGA for geometries and energies of diverselybonded materials (including covalent, metallic, ionic, hydrogen, and vdW bonds) at comparable efficiency. Often SCAN matches or improves upon the accuracy of a hybrid functional, at almostGGA cost. [1] J. Sun et al., Phys. Rev. Lett. 111, 106401 (2013). [2] J. Sun, A. Ruzsinszky, and J.P. Perdew, Phys. Rev. Lett. 115, 036402 (2015). [Preview Abstract] 
Monday, March 14, 2016 8:36AM  8:48AM 
A31.00002: SCAN+rVV10: A promising van der Waals density functional Haowei Peng, ZengHui Yang, Jianwei Sun, John Perdew The newly developed ``strongly constrained and appropriately normed'' (SCAN) metageneralizedgradient approximation (metaGGA) can generally improve over the nonempirical PerdewBurkeErnzerhof (PBE) GGA not only for strong chemical bonding, but also for the intermediaterange van der Waals (vdW) interaction. However, the longrange vdW interaction is still missing. To remedy this, we propose here pairing SCAN with the nonlocal correlation part from the rVV10 vdW density functional, with only two empirical parameters. The resulting \textit{SCAN+rVV10} yields excellent geometric and energetic results not only for molecular systems, but also for solids and layeredstructure materials, as well as the adsorption of benzene on coinage metal surfaces. Especially, SCAN+rVV10 outperforms all current methods with comparable computational efficiencies, accurately reproducing the three most fundamental parametersthe interlayer binding energies, inter, and intralayer lattice constantsfor 28 layeredstructure materials. Hence, we have achieved with SCAN+rVV10 a promising vdW density functional for general geometries, with minimal empiricism. [Preview Abstract] 
Monday, March 14, 2016 8:48AM  9:00AM 
A31.00003: The optimized effective potential of metageneralized gradient approximations in solids Zenghui Yang, John Perdew Unlike the local density approximation(LDA) and the generalized gradient approximation(GGA), calculations with metaGGAs are usually done according to the generalized KohnSham(gKS) formalism. The exchangecorrelation potential of the gKS equation is nonmultiplicative, which prevents systematic comparison of metaGGA bandstructures to those of the LDA and the GGA. We implement the optimized effective potential(OEP) of the metaGGA for periodic systems, which allows us to carry out metaGGA calculations in the same KS manner as for the LDA and the GGA. We apply the OEP to several popular metaGGAs, including the new SCAN functional[Phys. Rev. Lett. 115, 036402(2015)]. We find that the KS gaps of metaGGAs are close to those of GGAs, and they are smaller than the gKS gaps of metaGGAs. The wellknown grid sensitivity of metaGGAs is much more severe in OEP calculations. [Preview Abstract] 
Monday, March 14, 2016 9:00AM  9:12AM 
A31.00004: Characterization of Thin Film Materials using SCAN MetaGGA, an Accurate Nonempirical Density Functional IoanaGianina Buda, Christopher Lane, Bernardo Barbiellini, Adrienn Ruzsinszky, Jianwei Sun, John P. Perdew, Arun Bansil The exact groundstate properties of a material can be derived from the singleparticle KohnSham equations within the framework of the Density Functional Theory (DFT), provided the exact exchangecorrelation potential is known. The simplest approximation is the local density approximation (LDA), but it usually leads to overbinding in molecules and solids. On the other hand, the generalized gradient approximation (GGA) introduces corrections that expand and soften bonds. The newly developed nonempirical SCAN (stronglyconstrained and appropriatelynormed) MetaGGA [Phys. Rev. Lett. 115, 036402] has been shown to be comparable in efficiency to LDA and GGA, and to significantly improve LDA and the PerdewBurkeErnzerhof version of the GGA for groundstate properties such as equilibrium geometry and lattice constants for a number of standard datasets for molecules and solids. Here we discuss the performance of SCAN MetaGGA for thin films and monolayers and demonstrate improvements of predicted groundstate properties. Examples include graphene, phosphorene and MoS$_2$. [Preview Abstract] 
Monday, March 14, 2016 9:12AM  9:24AM 
A31.00005: Comparative firstprinciples study of cleansurface properties of metals Abhirup Patra, Jianwei Sun, John P. Perdew Metal surfaces are widely used in different applications from nanodevices to heterogeneous catalysis. Cleansurface properties such as the surface energy, work function and interlayer spacing importantly determine the behavior of metal surfaces. Prior work has been done to understand these properties using highlevel methods including the local density approximation (LDA) and the generalized gradient approximation (PBE). In this work, we study (111) (100) and (110) surfaces of Pt, Pd, Cu, Al, Au, Ag, Rh and Ru by extrapolation from a finite number of layers. These surfaces are studied using SCAN, a new member of the computationallyefficient metaGGA family of density functionals. We have compared the performance of SCAN and three other standard density functionals  LDA, PBE and PBEsol  to available experimental results. We find that the performance of the generalpurpose SCAN is at the level of the morespecialized PBEsol, giving accurate metallic properties. Ref: Jianwei Sun, Adrienn Ruzsinszky, John P Perdew, Strongly Constrained and Appropriately Normed Semilocal Density Functional, \textit{Physical Review Letters}115 (3), 036402 (2015). Supported by NSF under DMR1305135, CNS095884, and by DOE under DESC0012575, DEAC0205CH11231. [Preview Abstract] 
Monday, March 14, 2016 9:24AM  9:36AM 
A31.00006: A NonLocal, EnergyOptimized Kernel: Recovering SecondOrder Exchange and Beyond in Extended Systems Jefferson Bates, Savio Laricchia, Adrienn Ruzsinszky The Random Phase Approximation (RPA) is quickly becoming a standard method beyond semilocal Density Functional Theory that naturally incorporates weak interactions and eliminates selfinteraction error. RPA is not perfect, however, and suffers from selfcorrelation error as well as an incorrect description of shortranged correlation typically leading to underbinding. To improve upon RPA we introduce a shortranged, exchangelike kernel that is oneelectron selfcorrelation free for one and two electron systems in the highdensity limit. By tuning the one free parameter in our model to recover an exact limit of the homogeneous electron gas correlation energy we obtain a nonlocal, energyoptimized kernel that reduces the errors of RPA for both homogeneous and inhomogeneous solids. To reduce the computational cost of the standard kernelcorrected RPA, we also implement RPA renormalized perturbation theory for extended systems, and demonstrate its capability to describe the dominant correlation effects with a loworder expansion in both metallic and nonmetallic systems. Furthermore we stress that for normconserving implementations the accuracy of RPA and beyond RPA structural properties compared to experiment is inherently limited by the choice of pseudopotential. [Preview Abstract] 
Monday, March 14, 2016 9:36AM  10:12AM 
A31.00007: Semiclassical origins of density functionals Invited Speaker: Kieron Burke By careful numerical analysis of nonrelativistic atomic correlation energies, we show that (a) the local density approximation becomes relatively exact for the correlation energy as the atomic number approaches infinity, (b) we find the leading correction, which is about 38.5 milliHartrees per atom, (c) show how this correction dominates for larger atoms and (d) how to construct a generalized gradient approximation that respects this limit (See KB, A. Cancio, T. Gould, S. Pittalis, arXiv:1409.4834).\\ The relevance to density functional calculations will also be explained.\\ [Preview Abstract] 
Monday, March 14, 2016 10:12AM  10:24AM 
A31.00008: Semiclassical potential functionals for semiconductor quantum wells Attila Cangi Parabolic semiconductor quantum wells are considered promising candidates for constructing devices emitting radiation in the largely unexplored THz regime. However, progress is impeded by the difficulty of finetuning intersubband transitions in these quantum wells which is achieved by modifying the quantumwell geometry and mixing different materials. We predict the electronic structure of parabolic semiconductor quantum wells highly efficiently by iterating the KohnSham selfconsistent cycle without solving the KohnSham equations[1]. We achieve this by combining potential functionals[2,3] with a recently derived semiclassical approximation[4]. This (1) demonstrates our method's efficiency and accuracy for realistic systems and (2) illustrates its utility as a highthroughput method for predicting the electronic structure of technologically intriguing microstructures. [1] A. Cangi, C.R. Proetto, S. Pittalis, K. Burke, and E.K.U. Gross, submitted (2016). [2] A. Cangi, D. Lee, P. Elliott, K. Burke, and E.K.U. Gross, PRL 106, 236404 (2011). [3] A. Cangi, E. K. U. Gross, and K. Burke, PRA 88, 062505 (2013). [4] R.F. Ribeiro, D. Lee, A. Cangi, P. Elliott, and K. Burke, PRL 114, 050401 (2015). [Preview Abstract] 
Monday, March 14, 2016 10:24AM  10:36AM 
A31.00009: Thermal Corrections to Density Functional Simulations of Warm Dense Matter Justin Smith, Aurora PribramJones, Kieron Burke Present density functional calculations of warm dense matter often use the MerminKohnSham (MKS) scheme at finite temperature, but employ groundstate approximations to the exchangecorrelation (XC) free energy. In the simplest solvable nontrivial model, an asymmetric Hubbard dimer, we calculate the exact manybody energies, the exact MerminKohnSham functionals for this system, and extract the exact XC free energy. For moderate temperatures and weak correlation, we show this approximation is excellent, but fails for stronger correlations. Additionally, we use this system to test various conditions that must be satisfied. [Preview Abstract] 
Monday, March 14, 2016 10:36AM  10:48AM 
A31.00010: Study of the large reduced density gradient limit for the exchange energy Jose Gazquez, Javier CarmonaEspindola, Alberto Vela, Sam Trickey The generalized gradient approximation (GGA) for the KohnSham exchangecorrelation functional has become widely used in electronic structure calculations of small, medium and large systems, because it provides rather reasonable results with moderate computational effort. Usually the GGA for exchange (X) is expressed in terms of an analytical expression of the X enhancement function, Fx(s), where s is the reduced density gradient. When a nonempirical approach based on constraint satisfaction is followed, the analytical expression of Fx(s) is the result of interpolating between the small and larges limits. However, neither of those limits is uniquely defined. In both cases there are several possibilities. The present work is a study of the influence of the several larges limit possibilities upon the calculation of properties that depend on energy differences, versus those that depend on response functions, and excitation energies. [Preview Abstract] 
Monday, March 14, 2016 10:48AM  11:00AM 
A31.00011: Study of adiabatic connection in groundstate density functional theory Manoj Harbola, Rabeet Chauhan By employing modified [1] variational form of LeSech wavefunctions [2] for twoelectron systems, accurate wavefunctions for Helike atoms corresponding to their groundstate density are obtained for varying strength, given by a parameter $\alpha $ (0 $\le \alpha \le $1), of electronelectron interaction. Using these, it is shown explicitly that (i) the total energy varies almost linearly as a function of $\alpha $, and (ii) the ionization potential remains unchanged [3] as $\alpha $ is varied. Furthermore, kinetic energy contribution to the densityfunctional exchangecorrelation energy is calculated using the adiabatic connection formula [4] and shown to match that calculated on the basis of KohnSham calculation. Finally, the exchangecorrelation energy obtained for different values of $\alpha $ is employed to analyze several hybrid exchangecorrelation energy functionals in use. [1] R.S. Chauhan and M.K. Harbola, Chem. Phys. Lett. \textbf{639C}, 248(2015) [2] C. Le Sech, J. Phys. B: Atom. Mol. Opt. Phys. \textbf{30}, L47(1997) [3] M. Levy, J. P. Perdew and V. Sahni, Phys. Rev. A \textbf{30}, 2745(1984) [4] R. Harris and R.O. Jones, J. Phys. F: Met. Phys. 4 1170 (1974); D.C. Langreth and J.P. Perdew, Phys. Rev. B \textbf{15}, 2884 (1977) [Preview Abstract] 
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