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13 results on '"Schurkus, Henry F."'

1. Overcoming leakage in quantum error correction

Author

Miao, Kevin C., McEwen, Matt, Atalaya, Juan, Kafri, Dvir, Pryadko, Leonid P., Bengtsson, Andreas, Opremcak, Alex, Satzinger, Kevin J., Chen, Zijun, Klimov, Paul V., Quintana, Chris, Acharya, Rajeev, Anderson, Kyle, Ansmann, Markus, Arute, Frank, Arya, Kunal, Asfaw, Abraham, Bardin, Joseph C., Bourassa, Alexandre, Bovaird, Jenna, Brill, Leon, Buckley, Bob B., Buell, David A., Burger, Tim, Burkett, Brian, Bushnell, Nicholas, Campero, Juan, Chiaro, Ben, Collins, Roberto, Conner, Paul, Crook, Alexander L., Curtin, Ben, Debroy, Dripto M., Demura, Sean, Dunsworth, Andrew, Erickson, Catherine, Fatemi, Reza, Ferreira, Vinicius S., Burgos, Leslie Flores, Forati, Ebrahim, Fowler, Austin G., Foxen, Brooks, Garcia, Gonzalo, Giang, William, Gidney, Craig, Giustina, Marissa, Gosula, Raja, Dau, Alejandro Grajales, Gross, Jonathan A., Hamilton, Michael C., Harrington, Sean D., Heu, Paula, Hilton, Jeremy, Hoffmann, Markus R., Hong, Sabrina, Huang, Trent, Huff, Ashley, Iveland, Justin, Jeffrey, Evan, Jiang, Zhang, Jones, Cody, Kelly, Julian, Kim, Seon, Kostritsa, Fedor, Kreikebaum, John Mark, Landhuis, David, Laptev, Pavel, Laws, Lily, Lee, Kenny, Lester, Brian J., Lill, Alexander T., Liu, Wayne, Locharla, Aditya, Lucero, Erik, Martin, Steven, Megrant, Anthony, Mi, Xiao, Montazeri, Shirin, Morvan, Alexis, Naaman, Ofer, Neeley, Matthew, Neill, Charles, Nersisyan, Ani, Newman, Michael, Ng, Jiun How, Nguyen, Anthony, Nguyen, Murray, Potter, Rebecca, Rocque, Charles, Roushan, Pedram, Sankaragomathi, Kannan, Schurkus, Henry F., Schuster, Christopher, Shearn, Michael J., Shorter, Aaron, Shutty, Noah, Shvarts, Vladimir, Skruzny, Jindra, Smith, W. Clarke, Sterling, George, Szalay, Marco, Thor, Douglas, Torres, Alfredo, White, Theodore, Woo, Bryan W. K., Yao, Z. Jamie, Yeh, Ping, Yoo, Juhwan, Young, Grayson, Zalcman, Adam, Zhu, Ningfeng, Zobrist, Nicholas, Neven, Hartmut, Smelyanskiy, Vadim, Petukhov, Andre, Korotkov, Alexander N., Sank, Daniel, and Chen, Yu

Published
2023
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2. Quantum information phases in space-time: measurement-induced entanglement and teleportation on a noisy quantum processor

Author

Hoke, Jesse C., Ippoliti, Matteo, Abanin, Dmitry, Acharya, Rajeev, Ansmann, Markus, Arute, Frank, Arya, Kunal, Asfaw, Abraham, Atalaya, Juan, Bardin, Joseph C., Bengtsson, Andreas, Bortoli, Gina, Bourassa, Alexandre, Bovaird, Jenna, Brill, Leon, Broughton, Michael, Buckley, Bob B., Buell, David A., Burger, Tim, Burkett, Brian, Bushnell, Nicholas, Chen, Zijun, Chiaro, Ben, Chik, Desmond, Chou, Charina, Cogan, Josh, Collins, Roberto, Conner, Paul, Courtney, William, Crook, Alexander L., Curtin, Ben, Dau, Alejandro Grajales, Debroy, Dripto M., Barba, Alexander Del Toro, Demura, Sean, Di Paolo, Augustin, Drozdov, Ilya K., Dunsworth, Andrew, Eppens, Daniel, Erickson, Catherine, Faoro, Lara, Farhi, Edward, Fatem, Reza, Ferreira, Vinicius S., Burgos, Leslie Flores, Forati, Ebrahim, Fowler, Austin G., Foxen, Brooks, Giang, William, Gidney, Craig, Gilboa, Dar, Giustina, Marissa, Gosula, Raja, Gross, Jonathan A., Habegger, Steve, Hamilton, Michael C., Hansen, Monica, Harrigan, Matthew P., Harrington, Sean D., Heu, Paula, Hoffmann, Markus R., Hong, Sabrina, Huang, Trent, Huff, Ashley, Huggins, William J., Isakov, Sergei V., Iveland, Justin, Jeffr, Evan, Jones, Cody, Juhas, Pavol, Kafri, Dvir, Kechedzhi, Kostyantyn, Khattar, Tanuj, Khezri, Mostafa, Kieferová, Mária, Kim, Seon, Kitaev, Alexei, Klimov, Paul V., Klots, Andrey R., Korotkov, Alexander N., Kostritsa, Fedor, Kreikebaum, John Mark, Landhuis, David, Laptev, Pavel, Lau, Kim-Ming, Laws, Lily, Lee, Joonho, Lee, Kenny W., Lensky, Yuri D., Lester, Brian J., Lill, Alexander T., Liu, Wayne, Locharla, Aditya, Malone, Fionn D., Martin, Orion, McClean, Jarrod R., McCourt, Trevor, McEwen, Matt, Miao, Kevin C., Mieszala, Amanda, Montazeri, Shirin, Morvan, Alexis, Movassagh, Ramis, Mruczkiewicz, Wojciech, Neeley, Matthew, Neill, Charles, Nersisyan, Ani, Newman, Michael, Ng, Jiun H., Nguyen, Anthony, Nguyen, Murray, Niu, Murphy Yuezhen, O'Brien, Tom E., Omonije, Seun, Opremcak, Alex, Petukhov, Andre, Potter, Rebecca, Pryadko, Leonid P., Quintana, Chris, Rocque, Charles, Rubin, Nicholas C., Sank, Negar Saei Daniel, Sankaragomathi, Kannan, Satzinger, Kevin J., Schurkus, Henry F., Schuster, Christopher, Shearn, Michael J., Shorter, Aaron, Shutty, Noah, Shvarts, Vlad, Skruzny, Jindra, Smith, W. Clarke, Sterling, Rolando D. Somma George, Strain, Douglas, Szalay, Marco, Torres, Alfredo, Vidal, Guifre, Villalonga, Benjamin, Heidweiller, Catherine Vollgraff, White, Ted, Woo, Bryan W. K., Xing, Cheng, Yao, Z. Jamie., Yeh, Ping, Yoo, Juhwan, Young, Grayson, Zalcman, Adam, Zhang, Yaxing, Zhu, Ningfeng, Zobrist, Nicholas, Neven, Harmut, Babbush, Ryan, Bacon, Dave, Boixo, Sergio, Hilton, Jeremy, Lucero, Erik, Megrant, Anthony, Kelly, Julian, Chen, Yu, Smelyanskiy, Vadim, Mi, Xiao, Khemani, Vedika, and Roushan, Pedram

Subjects
High Energy Physics - Theory, Quantum Physics, Statistical Mechanics (cond-mat.stat-mech), High Energy Physics - Theory (hep-th), FOS: Physical sciences, Quantum Physics (quant-ph), Condensed Matter - Statistical Mechanics
Abstract

Measurement has a special role in quantum theory: by collapsing the wavefunction it can enable phenomena such as teleportation and thereby alter the "arrow of time" that constrains unitary evolution. When integrated in many-body dynamics, measurements can lead to emergent patterns of quantum information in space-time that go beyond established paradigms for characterizing phases, either in or out of equilibrium. On present-day NISQ processors, the experimental realization of this physics is challenging due to noise, hardware limitations, and the stochastic nature of quantum measurement. Here we address each of these experimental challenges and investigate measurement-induced quantum information phases on up to 70 superconducting qubits. By leveraging the interchangeability of space and time, we use a duality mapping, to avoid mid-circuit measurement and access different manifestations of the underlying phases -- from entanglement scaling to measurement-induced teleportation -- in a unified way. We obtain finite-size signatures of a phase transition with a decoding protocol that correlates the experimental measurement record with classical simulation data. The phases display sharply different sensitivity to noise, which we exploit to turn an inherent hardware limitation into a useful diagnostic. Our work demonstrates an approach to realize measurement-induced physics at scales that are at the limits of current NISQ processors.

Published
2023

3. Non-Abelian braiding of graph vertices in a superconducting processor

Author

Andersen, Trond I., Lensky, Yuri D., Kechedzhi, Kostyantyn, Drozdov, Ilya, Bengtsson, Andreas, Hong, Sabrina, Morvan, Alexis, Mi, Xiao, Opremcak, Alex, Acharya, Rajeev, Allen, Richard, Ansmann, Markus, Arute, Frank, Arya, Kunal, Asfaw, Abraham, Atalaya, Juan, Babbush, Ryan, Bacon, Dave, Bardin, Joseph C., Bortoli, Gina, Bourassa, Alexandre, Bovaird, Jenna, Brill, Leon, Broughton, Michael, Buckley, Bob B., Buell, David A., Burger, Tim, Burkett, Brian, Bushnell, Nicholas, Chen, Zijun, Chiaro, Ben, Chik, Desmond, Chou, Charina, Cogan, Josh, Collins, Roberto, Conner, Paul, Courtney, William, Crook, Alexander L., Curtin, Ben, Debroy, Dripto M., Barba, Alexander Del Toro, Demura, Sean, Dunsworth, Andrew, Eppens, Daniel, Erickson, Catherine, Faoro, Lara, Farhi, Edward, Fatemi, Reza, Ferreira, Vinicius S., Burgos, Leslie Flores, Forati, Ebrahim, Fowler, Austin G., Foxen, Brooks, Giang, William, Gidney, Craig, Gilboa, Dar, Giustina, Marissa, Gosula, Raja, Dau, Alejandro Grajales, Gross, Jonathan A., Habegger, Steve, Hamilton, Michael C., Hansen, Monica, Harrigan, Matthew P., Harrington, Sean D., Heu, Paula, Hilton, Jeremy, Hoffmann, Markus R., Huang, Trent, Huff, Ashley, Huggins, William J., Ioffe, Lev B., Isakov, Sergei V., Iveland, Justin, Jeffrey, Evan, Jiang, Zhang, Jones, Cody, Juhas, Pavol, Kafri, Dvir, Khattar, Tanuj, Khezri, Mostafa, Kieferová, Mária, Kim, Seon, Kitaev, Alexei, Klimov, Paul V., Klots, Andrey R., Korotkov, Alexander N., Kostritsa, Fedor, Kreikebaum, John Mark, Landhuis, David, Laptev, Pavel, Lau, Kim-Ming, Laws, Lily, Lee, Joonho, Lee, Kenny, Lester, Brian J., Lill, Alexander, Liu, Wayne, Locharla, Aditya, Lucero, Erik, Malone, Fionn D., Martin, Orion, McClean, Jarrod R., McCourt, Trevor, McEwen, Matt, Miao, Kevin C., Mieszala, Amanda, Mohseni, Masoud, Montazeri, Shirin, Mount, Emily, Movassagh, Ramis, Mruczkiewicz, Wojciech, Naaman, Ofer, Neeley, Matthew, Neill, Charles, Nersisyan, Ani, Newman, Michael, Ng, Jiun How, Nguyen, Anthony, Nguyen, Murray, Niu, Murphy Yuezhen, O'Brien, Thomas E., Omonije, Seun, Petukhov, Andre, Potter, Rebecca, Pryadko, Leonid P., Quintana, Chris, Rocque, Charles, Rubin, Nicholas C., Saei, Negar, Sank, Daniel, Sankaragomathi, Kannan, Satzinger, Kevin J., Schurkus, Henry F., Schuster, Christopher, Shearn, Michael J., Shorter, Aaron, Shutty, Noah, Shvarts, Vladimir, Skruzny, Jindra, Smith, W. Clarke, Somma, Rolando, Sterling, George, Strain, Doug, Szalay, Marco, Torres, Alfredo, Vidal, Guifre, Villalonga, Benjamin, Heidweiller, Catherine Vollgraff, White, Theodore, Woo, Bryan W. K., Xing, Cheng, Yao, Z. Jamie, Yeh, Ping, Yoo, Juhwan, Young, Grayson, Zalcman, Adam, Zhang, Yaxing, Zhu, Ningfeng, Zobrist, Nicholas, Neven, Hartmut, Boixo, Sergio, Megrant, Anthony, Kelly, Julian, Chen, Yu, Smelyanskiy, Vadim, Kim, Eun-Ah, Aleiner, Igor, and Roushan, Pedram

Subjects
Condensed Matter - Other Condensed Matter, Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics, Mesoscale and Nanoscale Physics (cond-mat.mes-hall), FOS: Physical sciences, Quantum Physics (quant-ph), Other Condensed Matter (cond-mat.other)
Abstract

Indistinguishability of particles is a fundamental principle of quantum mechanics. For all elementary and quasiparticles observed to date - including fermions, bosons, and Abelian anyons - this principle guarantees that the braiding of identical particles leaves the system unchanged. However, in two spatial dimensions, an intriguing possibility exists: braiding of non-Abelian anyons causes rotations in a space of topologically degenerate wavefunctions. Hence, it can change the observables of the system without violating the principle of indistinguishability. Despite the well developed mathematical description of non-Abelian anyons and numerous theoretical proposals, the experimental observation of their exchange statistics has remained elusive for decades. Controllable many-body quantum states generated on quantum processors offer another path for exploring these fundamental phenomena. While efforts on conventional solid-state platforms typically involve Hamiltonian dynamics of quasi-particles, superconducting quantum processors allow for directly manipulating the many-body wavefunction via unitary gates. Building on predictions that stabilizer codes can host projective non-Abelian Ising anyons, we implement a generalized stabilizer code and unitary protocol to create and braid them. This allows us to experimentally verify the fusion rules of the anyons and braid them to realize their statistics. We then study the prospect of employing the anyons for quantum computation and utilize braiding to create an entangled state of anyons encoding three logical qubits. Our work provides new insights about non-Abelian braiding and - through the future inclusion of error correction to achieve topological protection - could open a path toward fault-tolerant quantum computing.

Published
2022

4. Theoretical prediction of magnetic exchange coupling constants from broken-symmetry coupled cluster calculations.

Author

Schurkus, Henry F., Chan, Garnet Kin-Lic, Chen, Dian-Teng, Cheng, Hai-Ping, and Stanton, John F.

Subjects
*COUPLING constants, *MAGNETIC coupling, *FORECASTING, *EQUATIONS of motion, *SPIN-orbit interactions, *EXCHANGE interactions (Magnetism)
Abstract

Exchange coupling constants (J) are fundamental to the understanding of spin spectra of magnetic systems. Here, we investigate the broken-symmetry (BS) approaches of Noodleman and Yamaguchi in conjunction with coupled cluster (CC) methods to obtain exchange couplings. J values calculated from CC in this fashion converge smoothly toward the full configuration interaction result with increasing level of CC excitation. We compare this BS-CC scheme to the complementary equation-of-motion CC approach on a selection of bridged molecular cases and give results from a few other methodologies for context. [ABSTRACT FROM AUTHOR]

Published
2020
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5. Suppressing quantum errors by scaling a surface code logical qubit

Author

Acharya, Rajeev, Aleiner, Igor, Allen, Richard, Andersen, Trond I., Ansmann, Markus, Arute, Frank, Arya, Kunal, Asfaw, Abraham, Atalaya, Juan, Babbush, Ryan, Bacon, Dave, Bardin, Joseph C., Basso, Joao, Bengtsson, Andreas, Boixo, Sergio, Bortoli, Gina, Bourassa, Alexandre, Bovaird, Jenna, Brill, Leon, Broughton, Michael, Buckley, Bob B., Buell, David A., Burger, Tim, Burkett, Brian, Bushnell, Nicholas, Chen, Yu, Chen, Zijun, Chiaro, Ben, Cogan, Josh, Collins, Roberto, Conner, Paul, Courtney, William, Crook, Alexander L., Curtin, Ben, Debroy, Dripto M., Barba, Alexander Del Toro, Demura, Sean, Dunsworth, Andrew, Eppens, Daniel, Erickson, Catherine, Faoro, Lara, Farhi, Edward, Fatemi, Reza, Burgos, Leslie Flores, Forati, Ebrahim, Fowler, Austin G., Foxen, Brooks, Giang, William, Gidney, Craig, Gilboa, Dar, Giustina, Marissa, Dau, Alejandro Grajales, Gross, Jonathan A., Habegger, Steve, Hamilton, Michael C., Harrigan, Matthew P., Harrington, Sean D., Higgott, Oscar, Hilton, Jeremy, Hoffmann, Markus, Hong, Sabrina, Huang, Trent, Huff, Ashley, Huggins, William J., Ioffe, Lev B., Isakov, Sergei V., Iveland, Justin, Jeffrey, Evan, Jiang, Zhang, Jones, Cody, Juhas, Pavol, Kafri, Dvir, Kechedzhi, Kostyantyn, Kelly, Julian, Khattar, Tanuj, Khezri, Mostafa, Kieferová, Mária, Kim, Seon, Kitaev, Alexei, Klimov, Paul V., Klots, Andrey R., Korotkov, Alexander N., Kostritsa, Fedor, Kreikebaum, John Mark, Landhuis, David, Laptev, Pavel, Lau, Kim-Ming, Laws, Lily, Lee, Joonho, Lee, Kenny, Lester, Brian J., Lill, Alexander, Liu, Wayne, Locharla, Aditya, Lucero, Erik, Malone, Fionn D., Marshall, Jeffrey, Martin, Orion, McClean, Jarrod R., Mccourt, Trevor, McEwen, Matt, Megrant, Anthony, Costa, Bernardo Meurer, Mi, Xiao, Miao, Kevin C., Mohseni, Masoud, Montazeri, Shirin, Morvan, Alexis, Mount, Emily, Mruczkiewicz, Wojciech, Naaman, Ofer, Neeley, Matthew, Neill, Charles, Nersisyan, Ani, Neven, Hartmut, Newman, Michael, Ng, Jiun How, Nguyen, Anthony, Nguyen, Murray, Niu, Murphy Yuezhen, O'Brien, Thomas E., Opremcak, Alex, Platt, John, Petukhov, Andre, Potter, Rebecca, Pryadko, Leonid P., Quintana, Chris, Roushan, Pedram, Rubin, Nicholas C., Saei, Negar, Sank, Daniel, Sankaragomathi, Kannan, Satzinger, Kevin J., Schurkus, Henry F., Schuster, Christopher, Shearn, Michael J., Shorter, Aaron, Shvarts, Vladimir, Skruzny, Jindra, Smelyanskiy, Vadim, Smith, W. Clarke, Sterling, George, Strain, Doug, Szalay, Marco, Torres, Alfredo, Vidal, Guifre, Villalonga, Benjamin, Heidweiller, Catherine Vollgraff, White, Theodore, Xing, Cheng, Yao, Z. Jamie, Yeh, Ping, Yoo, Juhwan, Young, Grayson, Zalcman, Adam, Zhang, Yaxing, and Zhu, Ningfeng

Subjects
Quantum Physics, FOS: Physical sciences, Quantum Physics (quant-ph)
Abstract

Practical quantum computing will require error rates that are well below what is achievable with physical qubits. Quantum error correction offers a path to algorithmically-relevant error rates by encoding logical qubits within many physical qubits, where increasing the number of physical qubits enhances protection against physical errors. However, introducing more qubits also increases the number of error sources, so the density of errors must be sufficiently low in order for logical performance to improve with increasing code size. Here, we report the measurement of logical qubit performance scaling across multiple code sizes, and demonstrate that our system of superconducting qubits has sufficient performance to overcome the additional errors from increasing qubit number. We find our distance-5 surface code logical qubit modestly outperforms an ensemble of distance-3 logical qubits on average, both in terms of logical error probability over 25 cycles and logical error per cycle ($2.914\%\pm 0.016\%$ compared to $3.028\%\pm 0.023\%$). To investigate damaging, low-probability error sources, we run a distance-25 repetition code and observe a $1.7\times10^{-6}$ logical error per round floor set by a single high-energy event ($1.6\times10^{-7}$ when excluding this event). We are able to accurately model our experiment, and from this model we can extract error budgets that highlight the biggest challenges for future systems. These results mark the first experimental demonstration where quantum error correction begins to improve performance with increasing qubit number, illuminating the path to reaching the logical error rates required for computation., Main text: 6 pages, 4 figures. v2: Update author list, references, Fig. S12, Table IV

Published
2022

6. Efficient calculation of beyond RPA correlation energies in the dielectric matrix formalism.

Author

Beuerle, Matthias, Graf, Daniel, Schurkus, Henry F., and Ochsenfeld, Christian

Subjects
COMPUTATIONAL chemistry, DISPERSION (Atmospheric chemistry), HARTREE-Fock approximation, PHASE transitions, LAPLACE transformation, POLARIZATION (Electrochemistry)
Abstract

We present efficient methods to calculate beyond random phase approximation (RPA) correlation energies for molecular systems with up to 500 atoms. To reduce the computational cost, we employ the resolution-of-the-identity and a double-Laplace transform of the non-interacting polarization propagator in conjunction with an atomic orbital formalism. Further improvements are achieved using integral screening and the introduction of Cholesky decomposed densities. Our methods are applicable to the dielectric matrix formalism of RPA including second-order screened exchange (RPA-SOSEX), the RPA electron-hole time-dependent Hartree-Fock (RPA-eh-TDHF) approximation, and RPA renormalized perturbation theory using an approximate exchange kernel (RPA-AXK). We give an application of our methodology by presenting RPA-SOSEX benchmark results for the L7 test set of large, dispersion dominated molecules, yielding a mean absolute error below 1 kcal/mol. The present work enables calculating beyond RPA correlation energies for significantly larger molecules than possible to date, thereby extending the applicability of these methods to a wider range of chemical systems. [ABSTRACT FROM AUTHOR]

Published
2018
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7. Communication: An effective linear-scaling atomic-orbital reformulation of the random-phase approximation using a contracted double-Laplace transformation.

Author

Schurkus, Henry F. and Ochsenfeld, Christian

Subjects
*ATOMIC orbitals, *MATHEMATICAL reformulation, *LAPLACE transformation, *APPROXIMATION theory, *PERSONAL computers
Abstract

An atomic-orbital (AO) reformulation of the random-phase approximation (RPA) correlation energy is presented allowing to reduce the steep computational scaling to linear, so that large systems can be studied on simple desktop computers with fully numerically controlled accuracy. Our AO-RPA formulation introduces a contracted double-Laplace transform and employs the overlap-metric resolution-of-the-identity. First timings of our pilot code illustrate the reduced scaling with systems comprising up to 1262 atoms and 10 090 basis functions. [ABSTRACT FROM AUTHOR]

Published
2016
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8. Highly Accurate Random Phase Approximation Methods With Linear Time Complexity

Author

Schurkus, Henry F.

Subjects
FOS: Chemical sciences
Abstract

One of the key challenges of electronic structure theory is to find formulations to compute electronic ground-state energies with high accuracy while being applicable to a wide range of chemical problems. For systems beyond the few atom scale often computations achieving higher accuracies than the so called double-hybrid density functional approximations become prohibitively expensive. Here, the random phase approximation, which is known to yield such higher accuracy results has been developed from a theory applicable only to molecules on the tens of atoms scale into a highly accurate and widely applicable theory. To this end, a mathematical understanding has been developed that, without changing the computational complexity, allows to eliminate the error introduced by the resolution-of-the-identity approximation which had been introduced in the previous formulation. Furthermore, in this work a new formulation of the random phase approximation for molecules has been presented which achieves linear-scaling of compute time with molecular size - thereby expanding the realm of molecules that can be treated on this level of theory to up to a thousand atoms on a simple desktop computer. Finally, the theory has been matured to allow for use of even extensive basis sets without drastically increasing runtimes. Overall, the presented theory is at least as accurate and even faster than the original formulation for all molecules for which compute time is significant and opens new possibilities for the highly accurate description of large quantum chemical systems.

Published
2017
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9. Recent developments in the PySCF program package.

Author

Sun Q, Zhang X, Banerjee S, Bao P, Barbry M, Blunt NS, Bogdanov NA, Booth GH, Chen J, Cui ZH, Eriksen JJ, Gao Y, Guo S, Hermann J, Hermes MR, Koh K, Koval P, Lehtola S, Li Z, Liu J, Mardirossian N, McClain JD, Motta M, Mussard B, Pham HQ, Pulkin A, Purwanto W, Robinson PJ, Ronca E, Sayfutyarova ER, Scheurer M, Schurkus HF, Smith JET, Sun C, Sun SN, Upadhyay S, Wagner LK, Wang X, White A, Whitfield JD, Williamson MJ, Wouters S, Yang J, Yu JM, Zhu T, Berkelbach TC, Sharma S, Sokolov AY, and Chan GK

Abstract

PySCF is a Python-based general-purpose electronic structure platform that supports first-principles simulations of molecules and solids as well as accelerates the development of new methodology and complex computational workflows. This paper explains the design and philosophy behind PySCF that enables it to meet these twin objectives. With several case studies, we show how users can easily implement their own methods using PySCF as a development environment. We then summarize the capabilities of PySCF for molecular and solid-state simulations. Finally, we describe the growing ecosystem of projects that use PySCF across the domains of quantum chemistry, materials science, machine learning, and quantum information science.

Published
2020
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10. Exploring the Magnetic Properties of the Largest Single-Molecule Magnets.

Author

Schurkus HF, Chen D, O'Rourke MJ, Cheng HP, and Chan GK

Abstract

The giant {Mn 70 } and {Mn 84 } wheels are the largest nuclearity single-molecule magnets synthesized to date, and understanding their magnetic properties poses a challenge to theory. Starting from first-principles calculations, we explore the magnetic properties and excitations in these wheels using effective spin Hamiltonians. We find that the unusual geometry of the superexchange pathways leads to weakly coupled {Mn 7 } subunits carrying an effective S = 2 spin. The spectrum exhibits a hierarchy of energy scales and massive degeneracies, with the lowest-energy excitations arising from Heisenberg-ring-like excitations of the {Mn 7 } subunits around the wheel. We further describe how weak longer-range couplings can select the precise spin ground-state of the Mn wheels out of the nearly degenerate ground-state band.

Published
2020
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11. Accurate and Efficient Parallel Implementation of an Effective Linear-Scaling Direct Random Phase Approximation Method.

Author

Graf D, Beuerle M, Schurkus HF, Luenser A, Savasci G, and Ochsenfeld C

Abstract

An efficient algorithm for calculating the random phase approximation (RPA) correlation energy is presented that is as accurate as the canonical molecular orbital resolution-of-the-identity RPA (RI-RPA) with the important advantage of an effective linear-scaling behavior (instead of quartic) for large systems due to a formulation in the local atomic orbital space. The high accuracy is achieved by utilizing optimized minimax integration schemes and the local Coulomb metric attenuated by the complementary error function for the RI approximation. The memory bottleneck of former atomic orbital (AO)-RI-RPA implementations ( Schurkus, H. F.; Ochsenfeld, C. J. Chem. Phys. 2016 , 144 , 031101 and Luenser, A.; Schurkus, H. F.; Ochsenfeld, C. J. Chem. Theory Comput. 2017 , 13 , 1647 - 1655 ) is addressed by precontraction of the large 3-center integral matrix with the Cholesky factors of the ground state density reducing the memory requirements of that matrix by a factor of [Formula: see text]. Furthermore, we present a parallel implementation of our method, which not only leads to faster RPA correlation energy calculations but also to a scalable decrease in memory requirements, opening the door for investigations of large molecules even on small- to medium-sized computing clusters. Although it is known that AO methods are highly efficient for extended systems, where sparsity allows for reaching the linear-scaling regime, we show that our work also extends the applicability when considering highly delocalized systems for which no linear scaling can be achieved. As an example, the interlayer distance of two covalent organic framework pore fragments (comprising 384 atoms in total) is analyzed.

Published
2018
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12. Communication: Almost error-free resolution-of-the-identity correlation methods by null space removal of the particle-hole interactions.

Author

Schurkus HF, Luenser A, and Ochsenfeld C

Abstract

We present a method to improve upon the resolution-of-the-identity (RI) for correlation methods. While RI is known to allow for drastic speedups, it relies on a cancellation of errors. Our method eliminates the errors introduced by RI which are known to be problematic for absolute energies. In this way, independence of the error compensation assumption for relative energies is also achieved. The proposed method is based on the idea of starting with an oversized RI basis and projecting out all of its unphysical parts. The approach can be easily implemented into existing RI codes and results in an overhead of about 30%, while effectively removing the RI error. In passing, this process alleviates the problem that for many frequently employed basis sets no optimized RI basis sets have been constructed. In this paper, the theory is presented and results are discussed exemplarily for the random phase approximation and Møller-Plesset perturbation theory.

Published
2017
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13. Vanishing-Overhead Linear-Scaling Random Phase Approximation by Cholesky Decomposition and an Attenuated Coulomb-Metric.

Author

Luenser A, Schurkus HF, and Ochsenfeld C

Abstract

A reformulation of the random phase approximation within the resolution-of-the-identity (RI) scheme is presented, that is competitive to canonical molecular orbital RI-RPA already for small- to medium-sized molecules. For electronically sparse systems drastic speedups due to the reduced scaling behavior compared to the molecular orbital formulation are demonstrated. Our reformulation is based on two ideas, which are independently useful: First, a Cholesky decomposition of density matrices that reduces the scaling with basis set size for a fixed-size molecule by one order, leading to massive performance improvements. Second, replacement of the overlap RI metric used in the original AO-RPA by an attenuated Coulomb metric. Accuracy is significantly improved compared to the overlap metric, while locality and sparsity of the integrals are retained, as is the effective linear scaling behavior.

Published
2017
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