Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 510)
Virtual (March 2022); Time Zone: Pacific Time
Session A17: Density Functional Theory in Chemical Physics IFocus

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Sponsoring Units: DCP Chair: Aurora PribramJones, University of California, Merced Room: Room 209 
Monday, March 6, 2023 8:00AM  8:36AM 
A17.00001: Metageneralized gradient approximations for quantum materials Invited Speaker: Adrienn Ruzsinszky Although metageneralized gradient approximations (metaGGAs) [1,2] have been available for the materials science community for years, these approximations have not been harnessed for electronic structure to the extent that their potential indicates. Some of these metaGGAs like SCAN and r^{2}SCAN have undoubtedly become very popular for ground state applications [3]. MetaGGAs have the potential to bridge the gap between GGAs and hybrid density functionals. This opportunity has not been recognized and exploited far enough in materials science. MetaGGA approximations exhibit an extra flexibility via the kinetic energy density ingredient and functions built upon this ingredient. MetaGGAs are also implicit functionals of the electron density and explicit functionals of KohnSham orbitals. Increasing spatial nonlocality was shown to be associated with the kinetic energy density ingredient [4]. Quantum materials span a broad platform for a theorist with challenges for both structure and electronic properties. The physical situations that occur in these materials go far beyond the reach of any GGAlevelonly density functional. Phenomena such as charge density waves, band gaps and phase changes of topological materials require a framework with enough flexibility to capture all these physical situations. Within this talk I will present the recent evolution of some metaGGA density functionals and highlight the relevance of their ingredients through tests and applications [5] involving quantum materials. 
Monday, March 6, 2023 8:36AM  8:48AM 
A17.00002: Scaling up accurate density functional theory calculations with the embedded cluster density approximation Chen Huang The computational cost of KohnSham density functional theory (KSDFT) increases rapidly when advanced, orbitalbased exchangecorrelation (XC) energy functionals are used. To scale up such simulations, we have developed the embedded cluster density approximation (ECDA), which is a local correlation method formulated in the framework of DFT. In ECDA, for each atom, we select its nearby atoms to form a cluster. The rest of the system is the environment. The system's electron density is partitioned among the cluster and the environment, and the cluster's XC energy is calculated with an advanced XC energy functional. The cluster's XC energy is later projected onto its central atom. This procedure is performed for every atom in the system, and the total system's XC energy is obtained as the sum of these atomic XC energies. Since the clusters are defined by partitioning the electron density, rather than localizing the orbitals, ECDA is a nearly blackbox local correlation method and is applicable to systems having various bond types, such as ionic, metallic, and covalent bonds. We demonstrate ECDA's performance on molecules, metals, and oxides. In these examples, the exact exchange is employed as the advanced XC energy functional. Another appealing feature of ECDA is that it is a variational method and the analytical forces can be derived. We expect ECDA to be a simple, yet effective local correlation method for scaling up advanced DFT simulations in the future. 
Monday, March 6, 2023 8:48AM  9:00AM 
A17.00003: Performance of DispersionInclusive Density Functional Theory Methods for Energetic Materials Dana O'Connor Molecular crystals of energetic materials (EMs) are denser than typical molecular crystals and are characterized by distinct intermolecular interactions. To assess the performance of dispersioninclusive density functional theory (DFT) methods, we have compiled a data set of experimental sublimation enthalpies of 31 energetic materials. We evaluate the performance of three methods: the semilocal Perdew−Burke−Ernzerhof (PBE) functional coupled with the pairwise TkatchenkoScheffler (TS) dispersion correction, PBE with the manybody dispersion (MBD) method, and the PBEbased hybrid functional (PBE0) with MBD. Zeropoint energy contributions and thermal effects are described using the quasiharmonic approximation (QHA), including explicit treatment of thermal expansion, which we find to be nonnegligible for EMs. The lattice energies obtained with PBE0+MBD are the closest to experimental sublimation enthalpies with a mean absolute error of 9.89 kJ/mol. However, the stateoftheart treatment of vibrational and thermal contributions makes the agreement with experiment worse. Pressure−volume curves are also examined for six representative materials. For pressure−volume curves, all three methods provide reasonable agreement with experimental data with mean absolute relative errors of 3% or less. Most of the intermolecular interactions typical of EMs, namely nitroamine, nitro−nitro, and nitrohydrogen interactions, are more sensitive to the choice of the dispersion method than to the choice of the exchangecorrelation functional. The exception is π−π stacking interactions, which are also very sensitive to the choice of the functional. Overall, we find that PBE+TS, PBE+MBD, and PBE0+MBD do not perform as well for energetic materials as previously reported for other classes of molecular crystals. This highlights the importance of testing dispersioninclusive DFT methods for diverse classes of materials and the need for further method development. 
Monday, March 6, 2023 9:00AM  9:12AM 
A17.00004: Symmetry Breaking with the SCAN Density Functional Describes Strong Correlation in the Singlet Carbon Dimer John P. P Perdew, Shah Tanvir ur Rahman Chowdhury, Chandra Shahi, Aaron D Kaplan, Duo Song, Eric J Bylaska Abstract: The SCAN (strongly constrained and appropriately normed) metageneralized gradient approximation (metaGGA), which satisfies all 17 exact constraints that a metaGGA can satisfy, accurately describes equilibrium bonds that are normally correlated. With symmetry breaking, it also accurately describes some sd equilibrium bonds that are strongly correlated. While sp equilibrium bonds are nearly always normally correlated, the C_{2 }singlet ground state is known to be a rare case of strong correlation in an sp equilibrium bond. Earlier work that calculated atomization energies of the molecular sequence B_{2, }C_{2}, O_{2}, and F_{2 }in the local spin density approximation (LSDA), the PerdewBurkeErnzerhof (PBE) GGA, and the SCAN metaGGA, without symmetry breaking in the molecule, found that only SCAN was accurate enough to reveal an anomalous underbinding for C_{2}. This work shows that spin symmetry breaking in singlet C_{2}, the appearance of net up and downspin densities on opposite sides (not ends) of the bond, corrects that underbinding, with a small SCAN atomizationenergy error more like that of the other three molecules, suggesting that symmetrybreaking with an advanced density functional might reliably describe strong correlation. This talk also discusses some general aspects of symmetry breaking, and the insights into strong correlation that symmetrybreaking can bring. 
Monday, March 6, 2023 9:12AM  9:24AM 
A17.00005: Thermal and phase transition behavior of 2D quantum materials, enabled by machinelearned interatomic potentials Juan M MarmolejoTejada, Salvador BarrazaLopez, Martin A Mosquera Twodimensional (2D) quantum materials are expected to transform conventional electronics for a wide spectrum of applications. Here, we explore the combination of density functional theory (DFT) and machinelearned algorithmic training for the generation of momenttensor potentials (MTPs) to model singlelayer (1L) or bilayer (2L) transition metal dichalcogenides (TMDs). First, we use the trained MTPs for predicting the thermal transport properties of 1LMoS_{2}/WS_{2} lateral heterostructures, showing that the thermal conductivity of 2D alloys is highly resilient to sulfur vacancies, and enabling the finetuning of material's thermal properties for heat management and energy storage and conversion applications. Furthermore, we employ our trained MTPs for studying the temperaturedependent phase transition dynamics of Rstacked 2LTMDs, aiming to understand their paraelectric switching behavior. This is useful for modeling the ferroelectric properties of quantum systems that will be crucial components in the design and implementation of advanced electronic circuitry. 
Monday, March 6, 2023 9:24AM  9:36AM 
A17.00006: Abinitio Adaptive Density Embedding for Mesoscale Systems Xuecheng Shao, Michele Pavanello Density embedding [1] relies on a divideandconquer description of the electronic structure of large systems splitting them into smaller interacting subsystems. It is emerging as a powerful electronic structure method for largescale simulations of molecular condensed phases and interfaces [2]. However, due to limitations of the employed nonadditive density functionals, to date density embedding has been limited to approach weakly interacting subsystems. Additionally and more severely, when a single subsystem is very large (as in the case of interfaces of mesoscopic size), the computational cost is dominated by one of the large subsystems resulting in little overall gain compared to a fullfledged KohnSham DFT simulation. We will show that these problems can be elegantly resolved. We devised an adaptive density embedding method prescribing subsystem merging/splitting events whenever subsystems interact too strongly/weakly redistributing work and data in an efficient way[3]. We will also show that by making judicious use of orbitalfree DFT as a solver for metallic subsystems, mesoscopic moleculemetal interfaces can be modeled with an accuracy that is virtually identical to a KohnSham DFT simulation of the supersystem[4]. The resulting objectoriented Python implementations[5] constitute a blackbox, flexible and efficient electronic structure software for mesoscale systems. 
Monday, March 6, 2023 9:36AM  10:12AM 
A17.00007: Simulating Raman spectroscopy of doped 2D materials Invited Speaker: David A Strubbe Doping 2D materials can tune their electronic, optical, magnetic, catalytic, and mechanical properties, but it is difficult to get conclusive evidence from experiments about where the dopants are located, particularly in multilayer or bulk materials. Raman spectroscopy can be a powerful tool for characterization, but help from simulations is needed to interpret the spectra in terms of dopant location in substitutional or intercalation sites. I will present our studies of Raman spectroscopy in Ni and Redoped MoS_{2}, with densityfunctional perturbation theory. In Nidoped MoS_{2}, important for catalysis and lubrication, we find distinct fingerprints of the different doping sites, and analyze their origin in terms of activation of Ramaninactive modes, creation of new Nirelated modes, and shifts of existing modes [Guerrero et al., J. Phys. Chem. C 125, 13401 (2021)]. In Redoped MoS_{2}, important for electronics, we again find distinct characteristics of the doping sites, mostly in terms of shifts of the pristine Raman peaks. We show however that this peak shifts have a more complex origin than the simple ideas of strengthening or weakening of bonds as commonly used. Redoped MoS_{2} is ntype and therefore has a metallic density of states, preventing usual approaches for Raman calculations based on the static dielectric constant. We overcome this problem by using atomic Raman tensors from the pristine material. Our benchmarks show this is a generally applicable method for Raman calculations of metallic doped materials [Guerrero and Strubbe, J. Phys. Chem. C https://doi.org/10.1021/acs.jpcc.2c03999 (2022)]. In an experimental collaboration, we used these results to identify the location of dopants in samples of Redoped MoS_{2} that showed an unusual increase in nanoscale friction with the number of layers [Acikgoz et al., Nanotechnology 34, 015706 (2023)]. Finally, I will show some results from an undergraduate/graduate class project in which students calculated Raman spectra of MoS_{2x}Se_{2(1x)} monolayer alloys. 
Monday, March 6, 2023 10:12AM  10:24AM 
A17.00008: Quasiparticle band structures of halide double perovskites using Wannierlocalized optimally tuned screened range separated hybrid functionals Francisca Sagredo, Stephen E Gant, Guy Ohad, Jonah B Haber, Marina R Filip, Leeor Kronik, Jeffrey B Neaton Halide double perovskites are a promising new class of materials that offer an alternative to lead halide perovskites as suitable materials to use for solar cell applications, due to their greater stability and reduced susceptibility to environmental factors. Previous calculations of the band gaps using semilocal density functionals and the GW approximation, in conjunction with the lack of experimental data available for these class of materials, has left room for ambiguity in predicting the correct fundamental band gaps of these systems. Here we use the new state of the art, Wannierlocalized optimally tuned screened range separated hybrid (WOTSRSH) functional which has recently been shown to be a promising approach for a range of standard semiconductors, insulators, and lead halide perovskites. We compare and discuss the band gaps, band structures, and optical absorption spectra for double perovskites we obtain with this method with ab initio manybody perturbation theory, prior calculations, and experiment. We also discuss the use of WOTSRSH on other indirect gap materials. 
Monday, March 6, 2023 10:24AM  10:36AM 
A17.00009: Explore semilocal noninteracting kinetic energy functional and nonadditive noninteracting kinetic energy functional with neural network models Yuming Shi, Adam Wasserman The noninteracting kinetic energy (KE) functional of Density Functional Theory (DFT) has been for many decades an object of study for orbitalfree DFT and density embedding methods. Due to its comparatively large magnitude and to its highly nonlocal dependence on the density, the noninteracting KE functional remains extremely challenging to approximate accurately as an explicit functional of the densities. One of the most successful approximations, especially for modeling solid metals and semiconductors, is nonlocal functional. However, recent calculations show that the metaGGA level of approximation seems to be capable of yielding comparable accuracy. We explore the full potential of the metaGGA form for the noninteracting KE functional by using neural network models with exact conditions enforced. Moreover, the nonadditive noninteracting kinetic energy (NAKE), defined as the difference between the noninteracting KE of the entire system and the sum of the fragment kinetic energies, can be approximated as one separate quantity. We explore NAKE functionals designed for covalentlybonded fragments and fractional electrons in PartitionDFT. 
Monday, March 6, 2023 10:36AM  10:48AM 
A17.00010: A van der Waals Density Functional for Molecular Crystals Trevor Jenkins, Timo Thonhauser, Kristian Berland Since the development of the first van der Waals density functional by Dion et. al., the modeling of nonlocal correlation has evolved to more accurately describe larger and more varied types of structures. The newest generation of the vdWDF family, i.e. vdWDF3, constructed new forms of the nonlocal correlation functional and exchange and achieved improved accuracy over past van der Waals density functionals in modeling molecular dimers, layered structures, and adsorption systems. However due to competing interests within the parametrization of the functional, only limited accuracy was achieved for molecular crystals. Here we offer a new, highly accurate molecular crystal functional that is the result of a twofold solution to vdWDF3's shortcomings. To obtain accurate binding energies we make use of vdWDF3's flexible form of the nonlocal correlation, vital for the effective modeling of longrange dispersion interactions. In order to achieve accurate geometries we have also created a new variety of exchange in the generalized gradient approximation, one that allows for close fitting with experimental data. This new functional, which we name vdWDF3mc, outperforms all previously designed van der Waals density functionals and even the dispersion correction DFTD3 in tests on molecular crystal data sets such as the X23. We also discuss how our optimization procedure can be applied to other types of systems, offering a broad range of applications. 
Monday, March 6, 2023 10:48AM  11:00AM 
A17.00011: Machine learning modeling of the selfassembly of onedimensional nanostructures from twodimensional MoS_{2} monolayers with defect and strain engineering Akram Ibrahim, Can Ataca The chalcogen point vacancies, ubiquitous in a wide range of twodimensional (2D) transitionmetal dichalcogenides (TMDs), are experimentally observed to agglomerate forming extended line defects. We show that a discrepancy in the density of defects between the two chalcogen sides of MoS_{2} monolayers can lead to spontaneous curling and further selfassembly of various 1D nanostructures such as nanotubes and nanoscrolls. The large length and time scales needed to simulate this process make the usage of density functional theory (DFT) unfeasible. Instead of empirical potentials which suffer from their low accuracies, we develop a neural network potential (NNP) to drive our simulations at a comparable cost to empirical potentials while retaining the quantummechanical accuracy of DFT. The NNP model is first used to run Monte Carlo (MC) simulations to identify the longscale arrangements of vacancy defects at various vacancy concentrations. Then, NNP is utilized to run molecular dynamics (MD) simulations to model the selfassembly process. We provide a meticulous investigation of the effects of vacancy concentration and degree of strain on the selfassembly process. The usage of a machine learning potential helps to accurately approximate the experimental reality of the selfassembly process, which leads to a more accurate geometry of the formed 1D nanostructures to study their electronic and magnetic properties. 
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