Bulletin of the American Physical Society
2023 APS March Meeting
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session G17: Density Functional Theory in Chemical Physics IIIFocus Session
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Sponsoring Units: DCP Chair: Xuecheng Shao, Rutgers University - Newark Room: Room 209 |
Tuesday, March 7, 2023 11:30AM - 12:06PM |
G17.00001: Density Matrix Renormalization Group embedding in Kohn-Sham orbital environment Invited Speaker: Katarzyna Pernal The density matrix renormalization group (DMRG) method has already proved itself a very accurate computational method, which can treat large active spaces and capture the major part of strong correlation. Its application on larger molecules is, however, limited by its computational scaling. DFT approximations, on the other hand, allow for efficient calculations of electronic structure but they struggle in description of strong correlation. We present the first step in the direction of combining DMRG with density functional theory (DFT) by means of embedding DMRG in the orbital environment. |
Tuesday, March 7, 2023 12:06PM - 12:18PM |
G17.00002: Ozone: A failure of FLOSIC or standard DFT-like symmetry-breaking? Zahra Hooshmand Gharehbagh, Mark R Pederson There are well known cases where DFT requires spin disproportionation to determine qualitatively correct bond breaking and cases where such disproportionation remains at the equilibrium geometry. Ozone (O3) is an example of the latter based on conventional many-electron methods. The structure of the O3 molecule has been of great importance for over four decades due to its crucial role on life on planet earth. From a theoretical point of view, it offers a unique and challenging problem though its structure seems so simple for the advanced theories of today. In this talk we will present the results of the electronic structure study of O3 using density functional based approximations and show that for the first time, the ground state of the molecule is correctly described by DFT only when self-interaction-corrections (SIC) are taken into account; in particular Fermi-Löwdin Orbital-SIC. Using these results, we will show that while a broken spin-symmetry is found on the O3 molecule, the overall symmetry of the molecule, i.e. the symmetry of density, is preserved and the misconception of FLOSIC’s failure to correctly describe ozone [1] is resolved. [1] Hahn et al., J. Chem. Theory Comput. 13, 5823-5828 (2017). |
Tuesday, March 7, 2023 12:18PM - 12:30PM |
G17.00003: Capturing Strong Electron Correlation with Partition-DFT Yi Shi, Adam Wasserman Standard approximations for the exchange-correlation (XC) functional in Kohn-Sham-DFT (KS-DFT) typically lead to unacceptably large errors when applied to strongly-correlated electron systems. Partition-DFT is a formally exact reformulation of KS-DFT in which the ground-state density and energy of a system are obtained through self-consistent calculations on isolated fragments. Here we show how the typical errors of the standard approximations in KS-DFT can be largely avoided through Partition-DFT even when the same approximations are applied to the fragments. Our method is illustrated with Partition-DFT calculations on simple models of "strongly-correlated" hydrogen chains, for which numerically exact results are available through the Density Matrix Renormalization Group (DMRG). With a suitable "overlap approximation" (OA) for the partition energy, the binding curves of the hydrogen chains are significantly improved. We are exploring whether the OA also yields the correct power-law decay of the density dimerization orders observed in stretched hydrogen chains. |
Tuesday, March 7, 2023 12:30PM - 12:42PM |
G17.00004: Strong interaction and temperature effects in thermal density functional theory Aurora Pribram-Jones The strictly correlated electron approach to density functional theory, first proposed by Seidl and coworkers [1-4], offers a useful perspective on thermal density functional theory and one of its application areas, simulations in the warm dense matter regime. In this region of phase space, many of the assumptions of traditional Kohn-Sham density functional theory no longer hold, requiring exchange-correlation free energy approximations that include explicit temperature dependence and better handling of complicated ionization processes. Formal analysis of the strong interaction limit for thermal ensembles will be demonstrated using the asymmetric Hubbard dimer, accompanied by discussions of the finite-temperature uniform gas and the competition between strong interaction and temperature in complicated physical systems. |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G17.00005: Comparison of excitation energies from perturbative Ensemble Density Functional Theory approaches in real space Uday Panta, David A Strubbe Ensemble density functional theory (EDFT) is promising as an alternative to time-dependent density functional theory (TDDFT) for low-cost prediction of excitation energies and can handle double excitations more naturally. In particular, two perturbative approaches are the Direct Ensemble Correction (DEC), which has been tested on model systems and atoms [Yang et al., Phys. Rev. Lett. 119, 033003 (2017)], and the Ensemble "HOMO-LUMO gap" (or pEDFT), which has been benchmarked on small molecules [Gould et al., Phys. Chem. Lett. 13, 2452-2458 (2022)]. To assess how these EDFT based approaches handle more complicated systems, we implement these methods in the real-space Octopus code, which allows calculations of not only bigger systems, but also small model systems for comparison. Octopus has support for different theory levels and a variety of exchange-correlation functionals. We calculate excited states from DEC and pEDFT for various benchmark systems, and we compare results and convergence characteristics in real space to other standard excited-state approaches like linear-response TDDFT and TD Hartree-Fock. |
Tuesday, March 7, 2023 12:54PM - 1:30PM |
G17.00006: Ensemble density-functional theory of charged and neutral electronic excitations: Exact construction of energy levels and beyond Invited Speaker: Emmanuel Fromager It has been shown recently that charged and neutral electronic excitation processes can be described in principle exactly within a unified (so-called N-centered) ensemble density-functional theory (DFT) where the number of electrons is artificially held constant and equal to an integer. The practical advantage is that, unlike in conventional formulations of DFT, the derivative discontinuities of the density-functional exchange-correlation (xc) energy that occur when electrons are excited can essentially be removed from the theory. Their contribution to the physical excitation energies is then taken care of by the universal ensemble xc functional, through its ensemble weight dependence. In this talk, I will review the theory and discuss further extensions to spin-DFT and DFT for electrons and nuclei. If time permits, the extraction of linear response properties such as the oscillator strengths will also be discussed. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G17.00007: Plateaus in the Kohn-Sham potential of density-functional theory: analytical derivation and useful approximations Eli Kraisler, Nathan E Rahat Density functional theory (DFT) is the leading theoretical framework for electronic structure calculations, successfully describing a variety of materials and processes. However, the accuracy of DFT calculations crucially depends on the quality of the approximation used for the exchange-correlation functional, for which there is no exact expression. One of the features of the exact exchange-correlation potential which common approximations do not capture is the appearance of sharp spatial features, e.g. steps and plateaus. Their role is crucial for the description of such processes as ionization, dissociation and charge transfer. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G17.00008: How Important are Exact Conditions in Ensemble Density Functional Theory? Thais R Scott, John Kozlowski, Kieron Burke Ensemble density functional theory (EDFT) is resurfacing as a potential alternative to time-dependent density functional theory (TD-DFT) for computationally efficient and accurate excitation energies. As the field is developing, it is important to determine careful guidelines for reasonable approximations for novel and existing EDFT energy functionals. In this work, we prove various uniform scaling inequalities and test available EDFT functionals to determine if they meet these exact conditions. Our work highlights the importance of considering exact conditions when creating new functional for EDFT and is a precursor to future functional development based on a solid theoretical footing. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G17.00009: Mixing Stochastic-Deterministic Density Functional Theory In The PAW Formalism To Tackle Extreme Conditions Physics Vidushi Sharma, Alexander J White, Lee A Collins In computational materials modeling, density functional theory (DFT) is a powerful tool for studying systems ranging from just a few molecules to much more condensed phases. However, the finite temperature extension to DFT formulated by Mermin has a cubic scaling with system size and temperature, limiting its applicability for studying the physics of materials in extreme environments. In this talk, I will describe a novel proposal for a mixed DFT (mDFT) formalism that combines the stochastic and deterministic Kohn-Sham algorithms of DFT to study matter at any temperature [1]. We incorporate projector-augmented wave (PAW) potentials that improve the overall scaling of stochastic and mixed DFT toward a universal method across temperatures. Furthermore, we show that mDFT with PAW drastically reduces the computational effort without compromising the accuracy of purely deterministic DFT for studying the ground-state properties of materials. The time-dependent extension to mDFT enables us to simulate the dynamics within the Born-Oppenheimer approximation and beyond. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G17.00010: Using the generalized thermal adiabatic connection to analyze and build exchange-correlation free energy approximations Brittany P Harding Warm dense matter is a highly energetic phase found within planetary cores that exhibits properties of both plasmas and solids. Thermal density functional theory is commonly used to simulate this challenging phase, driving development of temperature-dependent approximations to the exchange-correlation free energy. The generalized thermal adiabatic connection (GTAC) introduces a fictitious temperature parameter in order to connect ground-state approximations to their finite-temperature counterparts. This approach will be demonstrated as an analytical tool and as a means to generate new approximations to entropic and kinetic free energy components. |
Tuesday, March 7, 2023 2:18PM - 2:30PM |
G17.00011: Generalized Gradient Approximation Made Thermal John Kozlowski, Kieron Burke Applications of warm dense matter include inertial confinement fusion, models of exoplanet interiors, and |
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