Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F01: Density Functional Theory and Beyond IFocus Recordings Available

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Sponsoring Units: DCP Chair: Jianwei Sun, Tulane Room: McCormick Place W175A 
Tuesday, March 15, 2022 8:00AM  8:36AM 
F01.00001: DensityCorrected SCAN MetaGGA* Invited Speaker: John P Perdew The strongly constrained and appropriately normed (SCAN) [1] metageneralized gradient approximation satisfies 17 exact constaints on the density functional for the exchangecorrelaton energy, and works well on its own selfconsistent density for many atoms, molecules, and condensed phases. But densitycorrected [2] SCAN, which evaluates SCAN on a "better" density such as that of HartreeFock theory, is often more accurate, and strikingly so for energy barriers [3] and for water clusters and liquid water [4]. For water, the accuracy of densitycorrected SCAN approaches that of coupled cluster theory. The likely reason for this is that HartreeFock theory more correctly tends to localize an integer electron number within each system fragment, while computationallyefficient density functionals may not [5]. 
Tuesday, March 15, 2022 8:36AM  8:48AM 
F01.00002: Testing the r^{2}SCAN density functional for the thermodynamical stability of solids with and without the van der Waals correction Manish Kothakonda, Aaron D Kaplan, Eric B Isaacs, Christopher Bartel, James W Furness, Jinliang Ning, John P Perdew, Christopher M Wolverton, Jianwei Sun Density functional theory has emerged as a powerful tool for predicting the thermodynamic stability of solidstate compounds, and improvements to the underlying exchangecorrelation functional can make those predictions more reliable. The newly developed r^{2}SCAN metaGGA functional enhances the numerical stability of SCAN [1] while retaining its accuracy on molecules and solids [2]. Meanwhile, the combination of SCAN with the rVV10 longrange correlation is known to be reliable for studying layered materials [3]. Here, we compare the performance of SCAN, r^{2}SCAN, SCAN+rVV10, and r^{2}SCAN+rVV10 for predicting formation energies, volumes, and band gaps. The test set consists of 1015 solids displaying a wide range of bonding environments, chemistries, and properties. Additionally, we assess the thermodynamic stability of compounds by calculating the enthalpy of decomposition with respect to the appropriate competing phases. 
Tuesday, March 15, 2022 8:48AM  9:00AM 
F01.00003: FLOSIC & FElectron Systems Alexander I Johnson, Mark R Pederson Systems containing felectrons are of growing importance as new applications exploiting their unique magnetic properties are developed. However, electronic structure theories lack the efficiency or accuracy necessary to study them. Density Functional Theory (DFT) offers an appealing approach to study felectron systems, yet selfinteraction error plagues the theory’s ability to accurately model felectrons. Additional treatment, such as FLOSIC [1], is generally required. NRLMOL has been generalized to include felectrons and FLOSIC, as well as improvements in efficiency which alleviate the difficulties of FLOSIC calculations, namely, finding FOD starting points and calculating the coulomb potential in a timely fashion. We present these improvements along with optimized FOD positions for Cs to Rn and examples of the effect of FLOSIC on ligated felectron systems. 
Tuesday, March 15, 2022 9:00AM  9:12AM 
F01.00004: The FermiLöwdin selfinteraction correction for spin transition systems Shiqi Ruan, Koblar A Jackson, Juan E Peralta, Adrienn Ruzsinszky (Semi)local density functional approximations underestimate the magnitude of the highestoccupied orbital (HO) eigenvalue, thereby narrowing the HOLU (lowestoccupied orbital) gap. This inaccuracy can be attributed to selfinteraction error (SIE). For spin transition systems like Fe(II) compounds, which show a transition between a lowspin state (S = 0) and a highspin state (S=2) at a critical temperature, this underestimation can be substantial [1,2], and leads to electron configurations with incorrect energy. In this work we have applied the FermiLöwdin selfinteraction correction [3], as well as different manybody perturbation approximations, to investigate how SIE affects the transition. 
Tuesday, March 15, 2022 9:12AM  9:24AM 
F01.00005: Complex FermiLöwdin orbitals for PerdewZunger selfinteraction correction Kushantha Withanage, Alexander I Johnson, Koblar A Jackson, Mark R Pederson The FermiLöwdin orbital selfinteraction correction [1] (FLOSIC) is a size extensive and unitarily invariant approach for implementing the PerdewZunger selfinteraction correction [2] (PZSIC) to density functional theory (DFT). The ingredients to define the FLO transformation are a set of orthonormal occupied orbitals and a set of parameters known as Fermiorbital descriptors (FODs). In the original FLOSIC implementation, FODs are defined as real vectors. Here we define FODs to be complex vectors. This leads to a complex transformation and complex FLOs. The complex FLOs are expected to be smoother/less noded localized orbitals. Such orbitals are important to obtain accurate and larger SIC corrections, particularly for semilocal functionals [3,4]. In this work, we find the optimal complex FODs for atoms and small molecules and calculate the complex FLOSIC total energies. Then we investigate the performance of the complex FLOSIC method for atomization energies of the molecules. 
Tuesday, March 15, 2022 9:24AM  9:36AM 
F01.00006: Lobedness, complex orbitals, and the selfinteraction energies of multiple bonds Puskar Bhattarai, Kushantha Withanage, Juan E Peralta, Mark R Pederson, Koblar A Jackson, John P Perdew A sizeextensive formulation of the PerdewZunger selfinteraction correction (PZSIC) [1] can be accomplished using localized Fermi Löwdin orbitals (FLOs) [2]. However, real FLOs are noded and semilocal functionals introduce an error that reflects the incipient division of one electron into fragments of noninteger electron number [3]. With real FLOs, molecules with multiple bonds are underbound and the FLOs associated with the multiple bonds are strongly noded. This suggests that the underbinding is directly linked to the nodality. We explore this link using a method that reduces the lobedness of these orbitals without altering the total electron density. This scheme effectively provides an upper bound on the PZSIC energy minimized in the variational space of complex orbitals [4,5] and yields a lower energy solution than with the original orbitals, thereby improving the atomization energies of the molecules. 
Tuesday, March 15, 2022 9:36AM  9:48AM 
F01.00007: Hyperfine Interactions for Small Molecules using FermiLöwdin Orbital Based SelfInteraction Corrected DFT Anri Karanovich, Koblar A Jackson, Kyungwha Park Hyperfine interactions play an important role in characterizing electronic structure using EPR or NMR, as well as in designing qubit systems. The major component of the hyperfine interaction energy, the Fermicontact (FC) term, is proportional to the electron spin density at the nuclear position. The FC term tends to be significantly underestimated in densityfunctional theory (DFT) methods due to selfinteraction errors (SIE), arising from approximate exchangecorrelation functionals, which results in significant electron and spindensity delocalization. A recently developed selfinteraction correction (SIC) method is based on FermiLöwdin orbitals (FLO), which depend on the positions of FermiOrbital Descriptors (FODs). The FLOSIC method has been successfully applied to various systems; however, its performance for the FC term has not been assessed yet. We carried out FLOSIC calculations on small transition metalbased molecules and computed the FC term in each case. The starting set of FODs for each calculation was generated using the symmetries of the system, as well as the Lewis structures predicted with natural bond orbital theory. The results from the FLOSIC method are compared with those from the SICfree generalizedgradient approximation method and experiments. 
Tuesday, March 15, 2022 9:48AM  10:00AM 
F01.00008: Bond length alternation of πconjugated polymers predicted by the FermiLöwdin orbital selfinteraction correction Duyen B Nguyen, Koblar A Jackson, Juan E Peralta πconjugated polymers have found practical applications in various fields, in part due to the high delocalization of electrons through the polymer axis. For electronic structure methods (ESMs), the correct description of the delocalization level can be characterized by the bond length difference between multiple and single bonds, or bond length alternation (BLA), and is a critical test for electron correlation effects and removal of selfinteraction error. The accurate theoretical determination of the BLA remains a significant challenge for traditional ESMs, such as density functional theory (DFT). Here, the BLAs of five oligomers are analyzed using the FermiLöwdin orbital selfinteraction correction (FLOSIC) method, which was proposed as a tool to remove oneelectron selfinteraction from approximate DFT. The BLAs for oligomers of increasing length were extrapolated to the polymer limit and compared to DFT and MP2 results. To analyze the delocalization level predicted by each method, the Natural Bond Orbital analysis was used to quantify the deviation of the relaxed structures from the ideal Lewis structures. Our results reveal that the FLOSIC improves the calculated BLA over LSDA and PBE, but it tends to overcorrect, in line with observations for other properties. 
Tuesday, March 15, 2022 10:00AM  10:12AM 
F01.00009: Chemical bonding theories as guides for selfinteraction corrections Kai Trepte, Sebastian Schwalbe, Simon Liebing, Wanja T Schulze, Jens Kortus, Hemanadhan Myneni, Aleksei Ivanov, Susi Lehtola Fermiorbital descriptors (FODs), i.e., electron positions, can be used to form FermiLöwdin orbitals (FLO), a special set of localized orbitals which can be used in combination with the PerdewZunger selfinteraction correction (SIC) in the FLOSIC method. We show how FODs can be used to initialize, interpret and justify SIC solutions in a common chemical picture within various SIC approaches.[1] 
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