Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S19: Building the Bridge to Exascale: Applications and Opportunities for Materials, Chemistry, and Biology IFocus Session Live
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Sponsoring Units: DCOMP DCMP DAMOP DCP Chair: Anouar Benali, Argonne National Laboratory |
Thursday, March 18, 2021 11:30AM - 12:06PM Live |
S19.00001: Accelerating Large-Scale Excited-State GW Calculations on Leadership Class HPC Systems Invited Speaker: Mauro Del Ben Large-scale GW calculations are state-of-the-art to accurately describe excited state phenomena in materials, which is critical for the design of novel new devices based on complex materials with applications in many fields. However, application of the GW method to complex systems is often perceived as being limited due to the high computational cost. Reduced time to solution can be achieved through novel methods, algorithms and optimal implementations on modern HPC systems. In particular accelerators such as GPUs can speed-up by order of magnitude conventional CPU-only implementations, and additionally reduce the energy per flop consumption. This talk showcases the various techniques used to achieve performance portability for the Material Science code BerkeleyGW on hybrid architectures targeting to accelerate large scale simulations with thousands of atoms. These techniques include the efficient use of accelerated libraries; asynchronous memory transfer, execution and overlap with MPI communication; batched operations; shared memory; and exploitation of high-performance memory to accelerate I/O. We achieve excellent strong and weak scaling on thousands of GPUs, and an order of magnitude or more reduction in time to solution compared to the CPU-only implementation. We demonstrate the scale of GW calculations to the order of over 10,000 electrons utilizing the entire Summit at OLCF (more than 27k GPUs) achieving over 100 PFLOP/s of double-precision performance and time to solution of the order of minutes. |
Thursday, March 18, 2021 12:06PM - 12:18PM Live |
S19.00002: From LSMS to MuST: Large scale first principles materials calculations at the exascale Markus Eisenbach, Xianglin Liu, Mariia Karabin, Swarnava ghosh, Yang Wang, Hanna Terletska, Wasim Mondal, Ka-Ming Tam, Yi Zhang, Liviu Chioncel We present recent development of our Locally-selfconsistent Multiple Scattering (LSMS) code for scalable large scale first principles density functional calculations of materials. A fundamental science driver for scalable, large scale, first principles calculations of materials is the need to understand states beyond periodic crystalline lattices. For large simulation cells, needed to describe extended electronic and magnetic orderings, defect states or disorder in alloys, the cubic scaling of traditional first principles methods has prevented direct calculations. The real space formalism of LSMS enables calculations for O(10,000 - 100,000) atoms on Summit. In preparation for exascale systems, we are extending the use of accelerators to enable the efficient calculation for embedding methods and forces. We present results and performance measurements for defects in high entropy alloys and non-collinear magnetism in disordered systems. The computational capabilities will be available in our Multiple Scattering Theory suite (MuST) [https://github.com/mstsuite] |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S19.00003: Recently Added Features, Scaling and Performance of the Real-Space MultiGrid (RMG) Code on Exascale Architectures Emil Briggs, Wenchang Lu, Jerry Bernholc lectronic structure calculations are hard to scale on massively parallel systems, and these challenges are compounded on CPU-GPU exascale architectures. The open-source RMG code exploits its real-space formulation to enable easy parallelization via domain decomposition but scalability to large node numbers of CPUs and GPUs requires careful attention to data structures and flow between nodes and between CPUs and GPUs located on the same node. We describe the solutions to these problems implemented in RMG as well as the results for large scale ab-initio calculations that use the recently implemented features of RMG: hybrid functionals, semi-local pseudopotentials and spin orbit coupling. For example, hybrid functional (HSE) calculations for up to 512-atom antifferromagnetic NiO supercells with 3584 semi-core and valence electrons exhibit excellent scaling up to 192 Summit CPU-GPU nodes, utilizing all 44 CPU cores and 6 GPUs per node. The RMG source code and build scripts for pre-exascale Summit, Cray XE-XK, clusters, Linux, Windows, and MacOS workstations are available at www.rmgdft.org together with help files and examples. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S19.00004: QMCPACK’s Exascale Performance Portability Strategies Paul Kent, Peter Doak, Mark Dewing, Ye Luo The upcoming Exascale era encompasses multiple accelerator technologies from different vendors. This poses both performance and portability challenge for science applications. Here we outline the strategies newly adopted by the open-source quantum monte Carlo code QMCPACK (https://qmcpack.org). The implemented algorithms provide very high accuracy for atoms, molecules and solids, including both metallic and insulating phases. We are targeting high performance on Intel, AMD and NVIDIA GPUs, continued high-performance on multicore CPUs, and a higher performance than the existing CUDA implementation. For real-space QMC algorithms we have adopted a new design and parallelization strategy in the Monte Carlo to increase the numerical work that can be exposed to the GPUs and to allow for the increase of asynchronous operations. OpenMP target offload is used to execute on the GPUs, with vendor libraries used where possible. We show current performance for materials calculations with a broad range of electron counts and analyze the remaining inefficiencies. |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S19.00005: A Pseudo-BCS Wavefunction from Density Matrix Decomposition: Application in Auxiliary-Field Quantum Monte Carlo Zhi-Yu Xiao, Hao Shi, Shiwei Zhang We present a method to construct pseudo-BCS wave functions from the one-body density matrix. The resulting many-body wave function, which can be produced for any fermion systems, including those with purely repulsive interactions, has the form of a number-projected BCS form, or antisymmetrized germinal power (AGP). Such wave functions provide a better ansatz for correlated fermion systems than a single Slater determinant, and often better than a linear combination of Slater determinants (for example from a truncated active space calculation). One application of the pseudo-BCS wave function is in auxiliary-field quantum Monte Carlo (AFQMC) calculations as the trial wave function to control the sign/phase problem. AFQMC is often among the most accurate general methods for correlated fermion systems. We show that the pseudo-BCS form further reduces the constraint bias and leads to improved accuracy compared to the usual Slater determinant trial wave functions, using the two-dimensional Hubbard model and real materials as examples. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S19.00006: GPU-Acceleration of the ELPA2 Distributed Eigensolver for Applications in Electronic Structure Theory Victor Yu, Jonathan Moussa, Pavel Kus, Andreas Marek, Peter Messmer, Mina Yoon, Hermann Lederer, Volker Blum The solution of eigenproblems is often a key computational bottleneck that limits the tractable system size of electronic structure theory. For large systems, these eigenproblems can easily exceed the capacity of a single computer and thus must be solved on distributed-memory parallel computers. The ELSI library facilitates large-scale electronic structure calculations by providing a unified interface to various fast and scalable eigensolvers and density matrix solvers. The ubiquitous adoption of hybrid CPU-GPU nodes in supercomputing opens up new opportunities to accelerate electronic structure calculations. We here present our (NVIDIA) GPU-oriented development of the ELPA two-stage tridiagonalization eigensolver (ELPA2), including GPU offloading based on the cuBLAS library, and CUDA kernels to speed up the back-transformation of eigenvectors, which can be the computationally most expensive part of the two-stage tridiagonalization algorithm. Robust choices that maximize GPU performance are identified. We demonstrate the performance of this GPU-accelerated eigensolver by a set of benchmark calculations on the Summit supercomputer. This work is supported by NSF under Award No. 1547580 and Award No. 1450280. |
Thursday, March 18, 2021 1:06PM - 1:18PM Live |
S19.00007: Discrete discontinuous basis projection (DDBP) method for large-scale electronic structure calculations. Qimen Xu, Phanish Suryanarayana, John Pask The large number of grid points per atom required for accurate real-space Kohn-Sham Density Functional Theory (DFT) calculations restricts their efficiency. In this work, we present an approach to accelerate such calculations several-fold, without loss of accuracy, by systematically reducing the cost of the key computational step: the determination of the Kohn-Sham orbitals spanning the occupied subspace. This is achieved by systematically reducing the dimension of the discrete eigenproblem that must be solved, through projection into a highly efficient discrete discontinuous basis. In calculations of quasi-1D, quasi-2D, and bulk metallic systems, we find that accurate energies and forces are obtained with 8–25 basis functions per atom, reducing the dimension of full-matrix eigenproblems by 1-3 orders of magnitude. |
Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S19.00008: MERA++: An Implementation of the Multi-scale Entanglement Renormalization Ansatz Gonzalo Alvarez The multi-scale entanglement renormalization ansatz (MERA) efficiently represents the ground state of short-ranged correlated electron Hamiltonians in any dimension [Vidal, 2006]. I will introduce MERA++, a computer program that implements MERA in two parts: a symbolic code and a numeric code. The symbolic code generates the MERA equations given a lattice, a model, and an ary for the MERA. The numeric code uses these equations to optimize the tensors that make up the MERA, and produces the ground state of the Hamiltonian in question, in any dimension, with bounded errors, and with systematic improvement by increasing the number of states that are kept. I will briefly discuss the technical challenges that MERA faces, when used to simulate (for example) the two dimensional and even three dimensional quantum Heisenberg models, without bias and with controlled errors. The code repositories for MERA++ are available at https://code.ornl.gov/gonzalo_3/merapp and at https://github.com/g1257/merapp. |
Thursday, March 18, 2021 1:30PM - 1:42PM Live |
S19.00009: Matrix Product States in the Continuum and Cold Atomic Gases Clayton Peacock, Aleksandar Ljepoja, Carlos J Bolech Cold atomic gases are an ideal laboratory to explore the physics of interacting degenerate quantum gases due to the high degree of tunability possible in the experiments. In particular, special trapping arrangements allow, among other things, to control the effective dimensionality of the systems. In this talk we present an update on the continuum formulation of Matrix Product States (cMPS) to describe one dimensional dilute quantum gases. The goal is to develop cMPS as an accurate predictive tool to plan and analyse past and future experiments. To that end, we shall present results for the cases of trapped single-species and multi-species bosonic and fermionic atoms, as well as their mixtures. When available, we make quantitative comparisons of cMPS results with the exact results for solvable cases. |
Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S19.00010: Overcoming the noncausality problem in nonlocal extensions of dynamical mean-field theory Steffen Backes, Jae-Hoon Sim, Silke Biermann In the last decade non-local extensions of the highly successful dynamical mean-field theory (DMFT) have become state of the art in order to access various phenomena that arise from nonlocal correlations. Though, it was realized that the success of these methods can be hampered by the emergence of noncausal features in the effective or observable quantities involved. We present a new approach of extending the local DMFT equations to nonlocal correlations, which preserves causality and has a physically intuitive interpretation. This approach has general implications for all related methods, and can be adapted with minimal effort for cluster, dual boson or fermion techniques. We benchmark the method for the exactly solvable dimer problem, which shows a significant improvement in the quality of the results compared to the standard approach. |
Thursday, March 18, 2021 1:54PM - 2:06PM Live |
S19.00011: Coupling interoperable software for quantum simulations of materials Marco Govoni, He Ma, Nan Sheng, Sijia Dong, Francois Gygi, Giulia Galli The functionality of most materials depends critically on the integration of dissimilar components and on the interfaces that arise between them. The description of such heterogeneous components requires the development and deployment of first principles methods, coupled to appropriate dynamical descriptions of matter. For the prediction and design of multiple properties of materials, it is essential to develop interoperable codes which can be efficiently coupled to each other to perform complex tasks. We discuss the coupled use of the WEST (http://west-code.org) and Qbox (http://qboxcode.org) codes to simulate the structural and spectroscopic characterization of materials1, including calculations of the electronic properties of insulators and semiconductors hosting optically addressable spin-defects for quantum information science2. We present simulations that include machine learning techniques and hybrid classical-quantum computations aimed at studying both optically activated processes at finite temperature and strongly correlated states3. |
Thursday, March 18, 2021 2:06PM - 2:18PM Live |
S19.00012: Implementation of spin-orbit coupling in the Real-space MultiGrid (RMG) code Wenchang Lu, Emil Briggs, Jerry Bernholc, Anh Pham, Panchapakesan Ganesh Spin-orbit coupling (SOC) plays an important role in materials containing heavy atoms, such as the emerging topological materials and f-electron metals. We implemented spin-orbit coupling in the open-source DFT electronic structure package RMG, www.rmgdft.org, which scales well from workstations to the latest CPU-GPU supercomputers. Fully relativistic pseudopotentials are used to describe the core electrons either in norm-conserving or ultrasoft form [1]. The coupling between the spin-up and spin-down electrons is mediated by the non-local pseudopotentials of the different spin components. Non-collinear magnetism, present in many multiferroic materials, is handled through a similar formalism. The calculated band structure of bulk Pt agrees very well with the result from the plane-wave based Quantum Espresso. We have also studied the band gap dependence on the thickness of thin-films of the topological material MnBi2Te4, in calculations that included up to 5,200 electrons. Our results are in good agreement with those obtained by VASP. This implementation enables us to explore effects of local- as well as extended-heterogeneities in thin-films of topological quantum materials and compare with experimental measurements. |
Thursday, March 18, 2021 2:18PM - 2:30PM Live |
S19.00013: Magnetic and charge orders in the ground state of the 2D repulsive Hubbard model Hao Xu, Mingpu Qin, Hao Shi, Yuan-Yao He, Ettore Vitali, Shiwei Zhang We systematically study the ground state of the two-dimensional repulsive Hubbard model as a function of doping and interaction strengths, using the auxiliary field quantum Monte-Carlo (AFQMC) method combined with a self-consistent constraint to control the sign problem. We focus on the spin and charge correlations, applying pinning fields to break translational symmetry and computing the spin and charge densities to probe the emergence of long-range order and collective modes. A phase diagram of spin-density waves is obtained. The effect of next-nearest-neighbor hopping is examined. The relation between the magnetic and pairing correlations will be discussed. |
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