Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session R25: Assigning Structures to Spectra Using Density Functional Theory: Method and Applications IVFocus Live
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Sponsoring Units: DCP Chair: Benjamin Janesko, Texas Christian Univ; Giovanni Scalmani, Gaussian, Inc. |
Thursday, March 18, 2021 8:00AM - 8:12AM Live |
R25.00001: Density matrix embedding theory for multi-band models and ab initio materials Zhi-Hao Cui, Garnet Chan Accurate description of correlated materials remains an essential challenge in the condensed matter physics. Quantum embedding theory provides an economical way to treat large system with local information from small fragments. In this work, we will discuss the formulation of density matrix embedding theory (DMET) for both multi-band lattice models and ab initio solids, with an emphasize on the unified framework and its efficient implementation. We applied DMET to the three-band Hubbard model to study the magnetic and superconducting ground-state phase diagram of high-Tc cuprates. We also benchmarked the ab initio DMET by calculating energy, equation-of-state and spin correlation function of realistic materials (h-BN, Si and NiO) with large embedding cluster up to 300 orbitals. |
Thursday, March 18, 2021 8:12AM - 8:48AM Live |
R25.00002: DFT error origins in open-shell d- and f-electron compounds revealed from SCAN’s performance: self-interaction error, strong correlation, or both? Invited Speaker: Jianwei Sun Compounds with open-shell d- and f-electrons, often exhibiting exotic properties and dubbed as correlated materials characterized by a strong inter-electronic Hubbard U, present great challenges to density functional theory (DFT), one of the most widely used electronic structure theories. DFT in principle is exact for the ground state total energy, while its exchange correlation energy has to be approximated in practice. There are two major error sources in a DFT calculation for correlated materials: 1) the strong correlation (SC) originating from a degeneracy or near-degeneracy closely related to Hubbard U, for example, the near-degeneracy of the partially filled d-subshells, and 2) the self-interaction error (SIE) due to the imperfect cancellation of the spurious classical Coulomb interaction between an electron and itself. In this talk, I will show that, without explicitly involving Hubbard U, the strongly-constrained and appropriately-normed (SCAN) density functional [1] gives significantly improved descriptions of the structural, energetic, electronic, and magnetic properties of correlated materials, including transition metal monoxides [2], high-Tc cuprate superconductors [3,4], and SmB6 [5], previously believed to be inaccessible to DFT. I will further explain the reasons behind SCAN’s improvement, showing its reduction in SIE and the help from spin symmetry breaking if SC is present. Outlooks on further improving density functionals for correlated materials will be discussed. |
Thursday, March 18, 2021 8:48AM - 9:00AM Live |
R25.00003: Preserving Symmetry and Degeneracy in the Localized Orbital Scaling Correction Aaron Mahler, Neil Qiang Su, Weitao Yang Density Functional Theory (DFT) has proven to be an invaluable tool for chemical predictions. However, standard density functional approximations (DFAs) can be inadequate in cases where nearly degenerate orbital energies play a key role such as dissociation energies, reaction barriers, and band gaps. Traditionally, these problems stem from self-interaction error. Recently, they have been identified as arising instead from delocalization error in DFAs, which stems from an incorrect treatment of fractional electron charge. The localized orbital scaling correction (LOSC) was introduced to correct for this error, which greatly improves DFA descriptions of band gaps, photoemission spectra, and dissociation limits of cationic species [1]. However, the original method did not preserve system symmetries and degeneracies. In this talk, we present the newest implementation of LOSC [2] that addresses system symmetry and more robustly preserves system degeneracies. This is mainly accomplished by the localized orbitals produced by the newest version of LOSC, which obey a subset of the system symmetry when allowed. |
Thursday, March 18, 2021 9:00AM - 9:12AM Live |
R25.00004: Nonlocal Kinetic Energy Functional Enables Reliable Large-scale Electronic Structure Simulations Wenhui Mi, Michele Pavanello Orbital-Free DFT (OF-DFT) and subsystem DFT (sDFT) are two promising approaches for large-scale electronic structure simulations, owing to their computational cost is linear scaling with system size. The common central ingredient of these two approaches is the kinetic energy functional (KEDF) which determines the accuracy of the performance. Unfortunately, with the available KEDFs, systems having highly inhomogeneous electron densities still fall outside OF-DFT's range of applicability. In sDFT, Currently employed KEDFs are at most semi-local, and simulations only included systems composed of weakly interacting subsystems. Recently, we made considerable progress in addressing this problem by proposing a new generation of nonlocal KEDFs that features correct asymptotic and ability to handle highly inhomogeneous electron densities. With these KEDFs, OF-DFT achieves close to chemical accuracy for the electronic energy for quantum dots and metal clusters. Benchmarks for the various bonded systems show that the new nonlocal sDFT considerably improves the computed interaction energies and electron densities compared to commonly employed (semi) local sDFT. Our work shows that the new generation of nonlocal KEDF enables both OF-DFT and sDFT for reliable large-scale simulations. |
Thursday, March 18, 2021 9:12AM - 9:24AM Live |
R25.00005: Cheap and reliable optimization of excited state orbitals with the Square Gradient Minimization (SGM) approach. Diptarka Hait, Martin P Head-Gordon Orbital optimized (OO) excited state methods eliminate many of the shortcomings of linear-response theories like TDDFT or EOM-CCSD for excited states with charge transfer, double or core excitation character. However, use of OO methods has been hindered by the risk of “variational collapse” from excited state solutions (typically saddle points of energy) to the ground state. We present an orbital optimization scheme based on square gradient minimization (SGM) that reliably converges to excited state solutions. The computational cost of SGM is only 2-3 times the cost of ground state orbital optimization (per iteration). We subsequently demonstrate that OO-DFT with SGM can predict energies of doubly excited states to significantly greater accuracy than expensive coupled cluster approaches (that often have > 1 eV error). Similarly, we demonstrate that OO-DFT approaches predict core excitation energies to < 0.5 eV RMS error for both closed and open-shell systems. In contrast, TDDFT typically has > 10 eV error and EOM-CCSD often fails qualitatively for open-shell cases. OO-DFT with SGM thus permits reliable simulation of both static and transient X-ray absorption spectra, which can be employed to interpret experimental studies of chemical dynamics. |
Thursday, March 18, 2021 9:24AM - 9:36AM Live |
R25.00006: The Application of Topological Quantum Chemistry in Electrides Si-Min Nie, Yuting Qian, Jiacheng Gao, Zhong Fang, Hongming Weng, Zhijun Wang The recently developed theory of topological quantum chemistry (TQC) has built a close connection between band topology in momentum space and orbital characters in real space. It provides an effective way to diagnose topological materials, leading to the discovery of lots of topological materials after the screening of all known nonmagnetic compounds. On the other hand, it can also efficiently reveal spacial orbital characters, including average charge centers and site-symmetry characters. By using the TQC theory, we demonstrate that the electrides with excess electrons serving as anions at vacancies can be well identified by the analysis of band representations (BRs), which cannot be expressed as a sum of atomic-orbital-induced band representations (aBRs). By computing the irreducible representations of electronic states, we find that the floating bands (formed by the excess electrons) belong to the BRs induced from the ‘pseudo-orbitals’ centered at vacancies, providing a promising avenue to pursue more electrides in ionic crystals. |
Thursday, March 18, 2021 9:36AM - 9:48AM Live |
R25.00007: Accurate lattice dynamics of cuprates from first principles Jinliang Ning, Christopher Lane, Matthew Matzelle, Bahadur Singh, Bernardo Barbiellini, Robert Markiewicz, Arun Kumar Bansil, Jianwei Sun The role lattice dynamics play in unconventional high-temperature superconductivity is unclear and is still vigorously debated. Theoretical insights into this problem have long been frustrated by the absence of an accurate first-principles description of the electronic, magnetic, and lattice degrees of freedom. Utilizing the recently constructed SCAN meta-GGA density functional [1] we find the calculated phonon dispersions of YBa2Cu3O6 in excellent accord with experimental measurements. Moreover, we find the strong magnetoelastic coupling for key phonon modes to be crucial in reproducing the experimental results. The improved description of SCAN over PBE, LDA, and DFT+U, is attributed to the holistic picture SCAN provides, where charge, magnetism, and lattice dynamics are treated on the same footing [2]. This work paves the way for further studies on the coupling between quasiparticles in cuprates, which is vital for unveiling the secrets behind unconventional high temperature superconductivity. |
Thursday, March 18, 2021 9:48AM - 10:24AM Live |
R25.00008: New Density Functional Methods to Compute Molecular Spectra:
Local Hybrid Functionals, Magnetic Resonance, and more Invited Speaker: Martin Kaupp This talk will cover various recent developments of modern DFT methods to compute molecular |
Thursday, March 18, 2021 10:24AM - 10:36AM Live |
R25.00009: Effective, Nostalgic, and Accurate: Generalized Basis Set for Core-Hole Excited State Derived from Slater’s Rule Jin Qian, David Prendergast Accurate estimates of core excitation energies of molecular systems computed using quantum chemistry methods have remained elusive despite decades of published research exploring both theoretical accuracy and basis set representations. Efficient predictive approaches to this problem are of great use in the interpretation of X-ray photoelectron spectroscopy, for example. Here, we deconvolute the numerical aspects of this problem by focusing on physically motivated contracted Gaussians that better reproduce the core-excited atomic orbitals, motivated by Slater’s rules. Armed with these core-excited basis sets, total energy differences, computed via the delta-SCF methodology employing hybrid exact-exchange functionals are sufficient to reproduce core-excitation energies within experimental accuracy (~0.1eV). We also highlight a physically motivated range of variability in the core level binding energy that is naturally tied to the expectation value of the local atomic charge and which provides a more realistic estimate of accuracy and transferability of a given theory than statistical accuracy estimates based on select choices of molecules. |
Thursday, March 18, 2021 10:36AM - 10:48AM Live |
R25.00010: Probing configuration of single atom catalysts via CO adsorption: Pt/CeO2(111) Dave Austin, Duy Le, Sampyo Hong, Talat Rahman Single Pt atoms adsorbed on CeO2(111) have been shown to produce a promising catalyst for a number of reactions. The question whether the Pt is adsorbed on the CeO2(111) surface at an oxygen vacancy site (Ptads) or that it is embedded in the subsurface of CeO2(111) (Ptemb) is still under debate. Using density functional theory calculations, we studied the stretching frequency of carbon monoxide adsorbed on to a single Pt atom supported on the CeO2(111) in the two configurations mentioned above. We find the C-O stretching frequency to be 2015 cm-1 and 2098 cm-1 for the CO molecule adsorbed at Ptemb and Ptads, respectively, suggesting that CO binds more strongly on Ptads than on Ptemd. In fact, we find that the binding energy of CO on Ptads and Ptemb are -0.963 eV and -0.64 eV, respectively. These results are serving as the basis for identifying the active sites in experiments being carried out at the Liu lab at UCF. We will present calculated infrared spectra and details of the electronic structure of the local environment for the Pt sites in question. We will also discuss the broader implications of our findings vis-à-vis the identification of active sites in oxide supported single atom catalysts. |
Thursday, March 18, 2021 10:48AM - 11:00AM On Demand |
R25.00011: Combining multireference methods with the density matrix renormalization group Henrik Larsson, Huanchen Zhai, Garnet Chan Standard multireference methods are limited by the size of the active orbital space. |
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