Bulletin of the American Physical Society
APS March Meeting 2023
Las Vegas, Nevada (March 510)
Virtual (March 2022); Time Zone: Pacific Time
Session A60: Quantum Embedding: Materials and Methods for MaterialsFocus

Hide Abstracts 
Sponsoring Units: DCOMP Chair: Tianyu Zhu, Yale University Room: Room 419 
Monday, March 6, 2023 8:00AM  8:36AM 
A60.00001: Invited Talk: Jernej MravljeSpectroscopies of Hund's metals within (DFT+)DMFT: electronic Raman response in Sr_{2}RuO_{4} Invited Speaker: Jernej Mravlje Spectrocopically, Hund's metals (e.g. ruthenates, ironbased superconductors) are characterized by multiplet splittings of the Hubbard bands and a particular shape of the quasiparticle peak associated to a twostage screening of the spin and orbital momentums. We recently found another feature, stemming from strong charge fluctuations in Hund's metals, which leads to a sidepeak at energy given exclusively by the value of Hund's rule coupling, that I will discuss based on dynamical meanfield theory results for a three orbital model Hund's metal. I will discuss the appearance of those features in photoemission and optical spectroscopies. 
Monday, March 6, 2023 8:36AM  8:48AM 
A60.00002: Magnetic Properties and Pseudogap Formation in InfiniteLayer Nickelates: Insights From the SingleBand Hubbard Model Thomas Schäfer, Marcel Klett, Philipp Hansmann We study the magnetic and spectral properties of a singleband Hubbard model for the infinitelayer nickelate compound LaNiO_{2}. As spatial correlations turn out to be the key ingredient for understanding its physics, we use two complementary extensions of the dynamical meanfield theory to take them into account: the cellular dynamical meanfield theory and the dynamical vertex approximation. Additionally to the systematic analysis of the doping dependence of the nonCurieWeiss behavior of the uniform magnetic susceptibility, we provide insight into its relation to the formation of a pseudogap regime by the calculation of the oneparticle spectral function and the magnetic correlation length. The latter is of the order of a few lattice spacings when the pseudogap opens, indicating a strongcoupling pseudogap formation in analogy to cuprates. 
Monday, March 6, 2023 8:48AM  9:24AM 
A60.00003: Moire Materials as laboratories for quantum embedding theories Invited Speaker: Andrew Millis Quantum embedding theories such as dynamical mean field theory approximate the full quantum dynamics and thermodynamics of an interacting electron system in terms of the properties of a ``quantum impurity model” (few degree of freedom quantum system coupled to non or weaklyinteracting bath). The downfolding of the full interacting system to the impurity model, and the adequacy of the quantum impurity model are important open issues in the theory of correlated quantum materials. ``Moire” materials comprised of two or more atomically thin sheets with a lattice constant mismatch or a relative twist angle have emerged as an important experimental platform for the investigation of correlated electron physics, due to the exceptional tunability of unit cell size and symmetry, electron concentration, interaction strength and other properties and to the ability to access parameter regimes inaccessible in conventional solids. This talk will summarize recent applications of embedding theories to experiments on Moire materials, including tests of the dynamical mean field picture of the metal insulator transition in the presence of Zeeman and orbital coupling to magnetic fields, the theory of transport near van Hove singularities and at high temperatures, and orbitalselective Mott and heavy fermion physics. 
Monday, March 6, 2023 9:24AM  9:36AM 
A60.00004: Green's function formulation of quantum defect embedding theory Marco Govoni, Nan Sheng, Christian W Vorwerk, Benchen Huang, Victor Yu, Giulia Galli We present a Green’s function formulation of the quantum defect embedding theory (QDET) where a double counting scheme is rigorously derived within the G_{0}W_{0} approximation [1]. We show the robustness of our methodology by applying the theory with the newly derived double counting scheme to several defects in diamond. We discuss a strategy to obtain converged results as a function of the size and composition of the active space. The results show that QDET, as implemented in the WEST code (http://westcode.org), is a promising approach to investigate strongly correlated states of defects in solids. Finally, we discuss how to carryout QDET calculations on GPUs [2] and noisy intermediatescale quantum computers [3]. 
Monday, March 6, 2023 9:36AM  9:48AM 
A60.00005: Comparing abinitio diffusion Monte Carlo and quantum embedding excited state calculations for an Fe^{3+} point defect in AlN Kevin G Kleiner, Cyrus E Dreyer, Lucas K Wagner Quantitative predictions of point defect excited states aid in materials design for optoelectronics and quantum information. However, certain defect excited states – such as those of substitutional Fe_{Al}^{3+}inAlN – require multideterminant wave functions [1]. Abinitio quantum embedding (QE) calculations balance accuracy and scalability by treating a small active space with an interacting theory. However, prior QE results for Fe^{3+}inAlN showed qualitative dependence on double counting and functional approximations [2], so higheraccuracy reference calculations are needed. 
Monday, March 6, 2023 9:48AM  10:00AM 
A60.00006: Statespecific Variational Quantum Monte Carlo for Point Defect Excited States Leon W Otis, Laura Gagliardi, Giulia Galli In recent years, much progress has been made in electronic structure calculations of spin defects from first principles, for example using quantum embedding theories [1,2]. However, several important controversies remain open in comparing different theoretical approaches and their respective results with experiments. Hence, the development of methods to obtain systematically improvable reference excitation energies of defects is a key priority. Quantum Monte Carlo techniques, particularly statespecific Variational Monte Carlo, have recently seen significant progress in the quality of the wave function ansatzes and optimization algorithms that can be employed for the description of excited states and have provided reliable excitation energies in molecular settings [3]. In this work, we extend the use of statespecific Variational Monte Carlo to the investigation of excited states of point defects in solids with the QMCPACK code and present preliminary results characterizing its accuracy, with the vacancy defect in diamond as an initial test case. 
Monday, March 6, 2023 10:00AM  10:12AM 
A60.00007: Lowenergy effective models for 2D hydrogen square lattices derived from first principles Sonali Joshi, Lucas K Wagner Effective model Hamiltonians use a small set of interactions to represent the physics of strongly correlated systems. To accurately represent real materials, effective models can be downfolded from firstprinciples calculations; however, using current methods, it can be difficult to assess systematic errors of the resulting models. The density matrix downfolding (DMD) procedure addresses this challenge by allowing the use of standard statistical analysis tools to quantify the errors of effective models fit to firstprinciples data [1]. 
Monday, March 6, 2023 10:12AM  10:24AM 
A60.00008: Functional theory of the spectral density via local embedding Andrea Ferretti, Tommaso Chiarotti, Nicola Marzari We address the problem of interacting electrons in an external potential by introducing the local spectral density as fundamental variable. First we formulate the problem using an embedding framework and prove a onetoone correspondence between a spectral density and the local, dynamical external potential playing the role of embedding selfenergy. Then, we use the Klein functional to (i) define a universal functional of the spectral density, (ii) introduce a variational principle for the total energy, and (iii) formulate a noninteracting mapping suitable for numerical applications. 
Monday, March 6, 2023 10:24AM  10:36AM 
A60.00009: AutoBZ.jl: An OpenSource Library for Automatic and Adaptive Brillouin Zone Integration Lorenzo X Van Munoz Brillouin zone integration is a standard operation in electronic structure calculations used to compute a wide range of physical observables. For systems at finite temperature with a significant scattering rate, represented by a large broadening factor $eta$, standard equispaced integration methods are highly effective. However, when the broadening $eta$ is small, adaptive methods become necessary to achieve converged results. The AutoBZ.jl library introduces both generic and specialized integration routines implementing automatic, optimized, and highorder accurate methods for integrals, with both large and small broadening, using Wannier interpolation. The package automatically selects the suitable integration routine for a given system and is optimized to use the irreducible Brillouin zone based on crystal symmetries. Written in Julia, the library is both extensible and performant, interfaces with Python, and obtains the abinitio Hamiltonian as standard output of Wannier90. Code examples are demonstrated using calculations of the density of states and optical conductivity of the correlated metal SrVO$_3$ with broadening down to the submeV scale. 
Monday, March 6, 2023 10:36AM  10:48AM 
A60.00010: Quantum Embedding Methods to investigate oxygen vacancies in Bulk MgO Shreya Verma, Christian W Vorwerk, Abhishek Mitra, Soumi Haldar, Giulia Galli, Laura Gagliardi Quantum embedding methods enable treating different parts of a system at distinct levels of electronic structure theory. For instance, the strongly correlated states of defects in solids may be treated at a higher level of theory than the rest of the system. Quantum defect embedding theory (QDET) [1,2] and periodic density matrix embedding theory (pDMET) [3] are two different methods, the former based on Green’s function embedding, and the latter using the Schmidt decomposition of the system’s density matrix. In this work we employ QDET (and the WEST code) and pDMET (and the PySCF code) to investigate the F^{0} center (neutral oxygen vacancy) in bulk MgO, which gives rise to a singly occupied localized defect state within the solid band gap. We investigate the orbital character of the defect state and compare the extrapolated vertical excitation energies obtained from the two embedding techniques. The active spaces derived from QDET and DMET are in good agreement with each other, however some of the computed excitation energies between multireference states differ. Work is in progress to analyze in detail the impact of all the approximations involved in QDET and DMET on the computed vertical excitation energies and compare them with experiments. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2023 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700