Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M01: Density Functional Theory and Beyond IIIFocus Recordings Available

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Sponsoring Units: DCP Chair: Aurora PribramJones, University of CA, Merced Room: McCormick Place W175A 
Wednesday, March 16, 2022 8:00AM  8:36AM 
M01.00001: The Connector Theory Approach: Principles and Development of new Density Functionals Invited Speaker: Lucia Reining

Wednesday, March 16, 2022 8:36AM  8:48AM 
M01.00002: Nonadiabatic functionals in TDDFT from the Connector Theory Lionel Lacombe, Lucia Reining, Matteo Gatti Timedependent density functional theory (TDDFT) has become a widely used method for the description of electronic spectra and responses, as well as an important tool for realtime electronic dynamics. However, these calculations use predominantly adiabatic functionals, i.e. with no memory (or frequency) dependence, for the exchange correlation potential (or kernel). With this limitation, accurate description of nonadiabatic phenomena such as resonantlydriven dynamics or dynamics far from the groundstate remains usually out of reach. Recently, a new approach called "Connector Theory" (COT), that makes use of the knowledge obtained on model systems to compute quantities in physical systems, has been developed. COT is in principle exact, but in practice approximations are needed to make it tractable. In this talk, we develop new nonadiabatic functionals for the exchangecorrelation potential using the COT approach. We present the various approximations and models chosen to derive our functionals and discuss the quality of the resulting timedependent quantities obtained in model and realistic systems. 
Wednesday, March 16, 2022 8:48AM  9:00AM 
M01.00003: Exchangecorrelation energy from exact and model Green's functions Steven Crisostomo, Kieron Burke Density functional theory (DFT) and Green’s function methods represent two large, and seemingly disparate, approaches to modeling strongly correlated physics. Green’s function based methods, such as Dynamical Mean Field Theory (DMFT), have proven effective in modeling properties of real systems with strong correlation. The intersections of DFT and Green’s function methods are still not well understood and the failures and pathologies of each remains a matter of open research. We derive a formula to determine the exchangecorrelation (XC) energy associated to exact and model Green’s functions. Using an exactly solvable interacting system, we show that our formula yields the exact XC energy, and we determine the XC energy associated with the Green’s function of DMFT. A formula connecting DFT quantities with Green’s functions provides a promising step towards better approximate forms of Green’s functions and density functionals. 
Wednesday, March 16, 2022 9:00AM  9:12AM 
M01.00004: Memory effects in TDDFT quadratic response theory DAVOOD DAR, Saswata Roy, Neepa T Maitra TDDFT is routinely used for calculations of excitations and response, achieving an unprecedented balance between accuracy and efficiency, while caution is applied for excitations problematic for the usual adiabatic approximations. In some applications, quantities from quadratic response theory are needed; for example, to obtain coupling matrix elements between excited states in nonadiabatic dynamics simulation. We explore the connection between spurious poles in these matrix elements and the lack of doubleexcitations in the adiabatic approximation to the kernel. We test the ability of a frequencydependent kernel that folds in these excitations to eliminate the divergence and produce reliable couplings for quadratic response. 
Wednesday, March 16, 2022 9:12AM  9:24AM 
M01.00005: Firstprinciples, spatially and temporallynonlocal exchangecorrelation kernel for jellium at all densities Aaron D Kaplan, Niraj K Nepal, Adrienn Ruzsinszky, Pietro Ballone, John P Perdew Accurate parameterizations of the groundstate exchangecorrelation energy of jellium have been known since Quantum Monte Carlo calculations in the 1980s. However, an equally accurate description of the timedependent linear response of an electron gas to an external perturbation has been elusive. Many extant models of the jellium exchangecorrelation kernel have substantial limitations: restrictions on the range of densities for which the model is accurate, restrictions to purely real or purely imaginary frequencies, etc. In this talk, I’ll motivate and describe a refinement [a] of the MCP07 [b] kernel that modifies its wavevector and frequency dependence, yielding a kernel that extrapolates to a very wide range of densities. The model kernel makes substantial corrections at low densities, where MCP07 is known to be least accurate, and fine tunes MCP07’s already excellent accuracy at typical metallic densities. Moreover, our model is numerically parameterized at all real and purely imaginary frequencies, a boon to further computational and theoretical applications. Excitedstate phenomena predicted with our model will also be discussed. 
Wednesday, March 16, 2022 9:24AM  9:36AM 
M01.00006: Simple ExchangeCorrelation Energy Functionals for Strongly Coupled LightMatter Systems based on the FluctuationDissipation Theorem Johannes Flick Recent experimental advances in strongly coupled lightmatter systems has sparked the development of general abinitio methods capable of describing interacting lightmatter systems from first principles. One of these methods, quantumelectrodynamical densityfunctional theory (QEDFT), promises computationally efficient calculations for large correlated lightmatter systems with the quality of the calculation depending on the underlying approximation for the exchangecorrelation functional. So far no true densityfunctional approximation has been introduced limiting the efficient application of the theory. In this paper, we introduce the first gradientbased density functional for the QEDFT exchangecorrelation energy derived from the adiabaticconnection fluctuationdissipation theorem. We benchmark this simpletoimplement approximation on small systems in optical cavities and demonstrate its relatively low computational costs for fullerene molecules up to C_{180} coupled to 400,000 photon modes in a dissipative optical cavity. This work now makes first principle calculations of much larger systems possible within the QEDFT framework effectively combining quantum optics with largescale electronic structure theory. 
Wednesday, March 16, 2022 9:36AM  9:48AM 
M01.00007: Accelerating TimeDependent Density Functional Theory with PhysicsInformed Neural Networks Karan Shah, Attila Cangi Timedependent density functional theory (TDDFT) is an important method for simulating dynamical processes in quantum manybody systems. We explore the feasibility of physicsinformed neural networks as a surrogate for TDDFT. We examine the computational efficiency and convergence behaviour of these solvers to stateoftheart numerical techniques on models and small molecular systems. The method developed here has the potential to accelerate the TDDFT workflow, enabling the simulation of largescale calculations of electron dynamics in matter exposed to strong electromagnetic fields, high temperatures, and pressures. 
Wednesday, March 16, 2022 9:48AM  10:00AM 
M01.00008: Singleparticleexact density functionals MartinIsbjorn Trappe We introduce a novel kind of density functionals for interacting manyfermion systems in the spirit of the Levyâ€”Lieb constrained search. In our approach all singleparticle contributions to the energy are represented by exact functionals, and only the functional for the interaction energy requires an approximation in terms of the singleparticle eigenstates. We discuss schemes for constructing the required approximate density matrices and report on benchmarking exercises that deliver groundstate energies, occupation numbers, and particle densities through evolutionary algorithms. 
Wednesday, March 16, 2022 10:00AM  10:12AM 
M01.00009: A reformulation of timedependent KohnSham theory in terms of the second time derivative of the density Walter Tarantino, Carsten A Ullrich The KohnSham approach to timedependent densityfunctional theory (TDDFT) can be formulated, in principle exactly, by invoking the forcebalance equation for the density, which leads to an explicit expression for the exchangecorrelation potential as an implicit density functional. It is shown that this suggests a reformulation of TDDFT in terms of the second time derivative of the density, rather than the density itself. The result is a timelocal KohnSham scheme of second order in time whose causal structure is more transparent than that of the usual KohnSham formalism. The scheme can be used to construct new approximations at the exchangeonly level and beyond, and it offers a straightforward definition of the exact adiabatic approximation. 
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