المؤلفون: Peng, Bo, Pathak, Himadri, Panyala, Ajay, Vila, Fernando D., Rehr, John J., Kowalski, Karol

مصطلحات موضوعية: Physics - Chemical Physics

الوصف: In this paper, we analyze the properties of the recently proposed real-time equation-of-motion coupled-cluster (RT-EOM-CC) cumulant Green's function approach [J. Chem. Phys. 2020, 152, 174113]. We specifically focus on identifying the limitations of the original time-dependent coupled cluster (TDCC) ansatz and propose an enhanced extended TDCC ansatz ensuring the exactness in the expansion limit. Additionally, we introduce a practical cluster-analysis-based approach for characterizing the peaks in the computed spectral function from the RT-EOM-CC cumulant Green's function approach, which is particularly useful for the assignments of satellite peaks when many-body effects dominate the spectra. Our preliminary numerical tests focus on reproducing, approximating, and characterizing the exact impurity Green's function of the three-site and four-site single impurity Anderson models using the RT-EOM-CC cumulant Green's function approach. The numerical tests allow us to have a direct comparison between the RT-EOM-CC cumulant Green's function approach and other Green's function approaches in the numerical exact limit.

URL الوصول: http://arxiv.org/abs/2406.00989

المؤلفون: Jost, Daniel, Lomeli, Eder G., Tang, Ta, Kas, Joshua J., Rehr, John J., Lee, Wei-Sheng, Jiang, Hong-Chen, Moritz, Brian, Devereaux, Thomas P.

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons

الوصف: X-ray spectroscopy has been a key method to determine ground and excited state properties of quantum materials with atomic specificity. Now, new x-ray facilities are opening the door to the study of pump-probe x-ray spectroscopy - specifically time-resolved x-ray absorption (trXAS) and time-resolved resonant inelastic x-ray scattering (trRIXS). In this paper we will present simulations of each of these spectroscopies using a time-domain full atomic multiplet, charge transfer Hamiltonian, adapted to study the properties of a generalized cluster model including a central transition metal ion caged by ligand atoms in a planar geometry. The numerically evaluated trXAS and trRIXS cross-sections for representative electron configurations $3d^9$ and $3d^8$ demonstrate the insights that can be obtained from charge transfer pumping, and how this nonequilibrium process affects ground and excited state properties. The straightforward characterization of the excitations in these systems, based on our analysis of the simulations, can serve as a benchmark for future experiments, as access to these time-resolved spectroscopic techniques becomes more widely available.

URL الوصول: http://arxiv.org/abs/2405.16025

المؤلفون: Kowalski, Karol, Bauman, Nicholas P., Low, Guang Hao, Roetteler, Martin, Rehr, John J., Vila, Fernando D.

مصطلحات موضوعية: Quantum Physics

الوصف: Theoretical descriptions of excited states of molecular systems in high-energy regimes are crucial for supporting and driving many experimental efforts at light source facilities. However, capturing their complicated correlation effects requires formalisms that provide a hierarchical infrastructure of approximations. These approximations lead to an increased overhead in classical computing methods, and therefore, decisions regarding the ranking of approximations and the quality of results must be made on purely numerical grounds. The emergence of quantum computing methods has the potential to change this situation. In this study, we demonstrate the efficiency of Quantum Phase Estimator (QPE) in identifying core-level states relevant to x-ray photoelectron spectroscopy. We compare and validate the QPE predictions with exact diagonalization and real-time equation-of-motion coupled cluster formulations, which are some of the most accurate methods for states dominated by collective correlation effects.

URL الوصول: http://arxiv.org/abs/2402.11418

المؤلفون: Windus, Theresa, Banda, Michael, Devereaux, Thomas, White, Julia C, Antypas, Katie, Coffey, Richard, Dart, Eli, Dosanjh, Sudip, Gerber, Richard, Hack, James, Monga, Inder, Papka, Michael E, Riley, Katherine, Rotman, Lauren, Straatsma, Tjerk, Wells, Jack, Baruah, Tunna, Benali, Anouar, Borland, Michael, Brabec, Jiri, Carter, Emily, Ceperley, David, Chan, Maria, Chelikowsky, James, Chen, Jackie, Cheng, Hai-Ping, Clark, Aurora, Darancet, Pierre, DeJong, Wibe, Deslippe, Jack, Dixon, David, Donatelli, Jeffrey, Dunning, Thomas, Fernandez-Serra, Marivi, Freericks, James, Gagliardi, Laura, Galli, Giulia, Garrett, Bruce, Glezakou, Vassiliki-Alexandra, Gordon, Mark, Govind, Niri, Gray, Stephen, Gull, Emanuel, Gygi, Francois, Hexemer, Alexander, Isborn, Christine, Jarrell, Mark, Kalia, Rajiv K, Kent, Paul, Klippenstein, Stephen, Kowalski, Karol, Krishnamurthy, Hulikal, Kumar, Dinesh, Lena, Charles, Li, Xiaosong, Maier, Thomas, Markland, Thomas, McNulty, Ian, Millis, Andrew, Mundy, Chris, Nakano, Aiichiro, Niklasson, AMN, Panagiotopoulos, Thanos, Pandolfi, Ron, Parkinson, Dula, Pask, John, Perazzo, Amedeo, Rehr, John, Rousseau, Roger, Sankaranarayanan, Subramanian, Schenter, Greg, Selloni, Annabella, Sethian, Jamie, Siepmann, Ilja, Slipchenko, Lyudmila, Sternberg, Michael, Stevens, Mark, Summers, Michael, Sumpter, Bobby, Sushko, Peter, Thayer, Jana, Toby, Brian, Tull, Craig, Valeev, Edward, Vashishta, Priya, Venkatakrishnan, V, Yang, C, Yang, Ping, Zwart, Peter H

URL الوصول: https://escholarship.org/uc/item/55z6k627

المؤلفون: Cardot, Charles, Kas, Joshua, Abramson, Jared, Rehr, John, Seidler, Gerald T.

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science

الوصف: Recent advances using Density Functional Theory (DFT) to augment Multiplet Ligand Field Theory (MLFT) have led to ab-initio calculations of many formerly empirical parameters. This development makes MLFT more predictive instead of interpretive, thus improving its value for understanding highly correlated 3d, 4d, and f-electron systems. Here, we explore a DFT + MLFT based approach for core-to-core K{\alpha} x-ray emission spectra (XES) and evaluate its performance for a range of transition metal systems. We find good agreement between theory and experiment, as well as the ability to capture key spectral trends related to spin and oxidation state. We also discuss limitations of the model in the context of the remaining free parameters and suggest directions forward.

URL الوصول: http://arxiv.org/abs/2304.14582

المؤلفون: Pathak, Himadri, Panyala, Ajay, Peng, Bo, Bauman, Nicholas P., Mutlu, Erdal, Rehr, John J., Vila, Fernando D., Kowalski, Karol

مصطلحات موضوعية: Physics - Chemical Physics

الوصف: We report the implementation of the real-time equation-of-motion coupled-cluster (RT-EOM-CC) cumulant Green's function method [J. Chem. Phys. 152, 174113 (2020)] within the Tensor Algebra for Many-body Methods (TAMM) infrastructure. TAMM is a massively parallel heterogeneous tensor library designed for utilizing forthcoming exascale computing resources. The two-body electron repulsion matrix elements are Cholesky-decomposed, and we imposed spin-explicit forms of the various operators when evaluating the tensor contractions. Unlike our previous real algebra Tensor Contraction Engine (TCE) implementation, the TAMM implementation supports fully complex algebra. The RT-EOM-CC singles (S) and doubles (D) time-dependent amplitudes are propagated using a first-order Adams--Moulton method. This new implementation shows excellent scalability tested up to 500 GPUs using the Zn-porphyrin molecule with 655 basis functions, with parallel efficiencies above 90\% up to 400 GPUs. The TAMM RT-EOM-CCSD was used to study core photo-emission spectra in the formaldehyde and ethyl trifluoroacetate (ESCA) molecules. Simulations of the latter involve as many as 71 occupied and 649 virtual orbitals. The relative quasiparticle ionization energies and overall spectral functions agree well with available experimental results.

URL الوصول: http://arxiv.org/abs/2301.04249

المؤلفون: Vila, Fernando D., Rehr, John J., Pathak, Himadri, Peng, Bo, Panyala, Ajay, Mutlu, Erdal, Bauman, Nicholas P., Kowalski, Karol

مصطلحات موضوعية: Physics - Chemical Physics, Quantum Physics

الوصف: Newly developed coupled-cluster (CC) methods enable simulations of ionization potentials and spectral functions of molecular systems in a wide range of energy scales ranging from core-binding to valence. This paper discusses results obtained with the real-time equation-of-motion CC cumulant approach (RT-EOM-CC), and CC Green's function (CCGF) approaches in applications to the water and water dimer molecules. We compare the ionization potentials obtained with these methods for the valence region with the results obtained with the CCSD(T) formulation as a difference of energies for N and N-1 electron systems. All methods show good agreement with each other. They also agree well with experiment, with errors usually below 0.1 eV for the ionization potentials. We also analyze unique features of the spectral functions, associated with the position of satellite peaks, obtained with the RT-EOM-CC and CCGF methods employing single and double excitations, as a function of the monomer OH bond length and the proton transfer coordinate in the dimer. Finally, we analyze the impact of the basis set effects on the quality of calculated ionization potentials and find that the basis set effects are less pronounced for the augmented-type sets.

URL الوصول: http://arxiv.org/abs/2205.14179

المؤلفون: Cardot, Charles A., Kas, Joshua J., Abramson, Jared E., Rehr, John J., Seidler, Gerald T.

المصدر: In Journal of Electron Spectroscopy and Related Phenomena January 2024 270

المؤلفون: Chen, Yiming, Chen, Chi, Zheng, Chen, Dwaraknath, Shyam, Horton, Matthew K, Cabana, Jordi, Rehr, John, Vinson, John, Dozier, Alan, Kas, Joshua J, Persson, Kristin A, Ong, Shyue Ping

المصدر: Scientific data. 8(1)

الوصف: The L-edge X-ray Absorption Near Edge Structure (XANES) is widely used in the characterization of transition metal compounds. Here, we report the development of a database of computed L-edge XANES using the multiple scattering theory-based FEFF9 code. The initial release of the database contains more than 140,000 L-edge spectra for more than 22,000 structures generated using a high-throughput computational workflow. The data is disseminated through the Materials Project and addresses a critical need for L-edge XANES spectra among the research community.

وصف الملف: application/pdf

URL الوصول: https://escholarship.org/uc/item/9m45379b

المؤلفون: Tzavala, Marilena, Kas, Joshua J., Reining, Lucia, Rehr, John J.

المصدر: Phys. Rev. Research 2, 033147 (2020)

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Other Condensed Matter

الوصف: Most currently used approximations for the one-particle Green's function G in the framework of many-body perturbation theory, such as Hedin's GW approximation or the cumulant GW+C approach, are based on a linear response approximation for the screened interaction W. The extent to which such a hypothesis is valid and ways to go beyond have been explored only very little. Here we show how to derive a cumulant Green's function beyond linear-response from the equation of motion of the Green's function in a functional derivative formulation. The results can be written in a compact form, which opens the possibility to calculate the corrections in a first principles framework using time-dependent density functional theory. In order to illustrate the potential importance of the corrections, numerical results are presented for a model system with a core level and two valence orbitals.
Comment: 9 pages, 1 figure

URL الوصول: http://arxiv.org/abs/2005.01857