Capabilities

Capabilities

Socorro: Code for Highly Scalable Density-Functional-Theory Calculations of Extended Systems

Laboratory

Sandia National Laboratories (SNL)

Capability Expert

Normand Modine, Alan Wright

Class

Computational Tools and Modeling

Node Readiness Category

2: High-Temperature Electrolysis (HTE)
2: Low-Temperature Electrolysis (LTE)
1: Photoelectrochemical (PEC)
2: Solar Thermochemical (STCH)

Description

Socorro is an electronic-structure code developed at Sandia National Laboratories to enable high-fidelity simulations of materials. The code can be used to perform spin-polarized and non-spin-polarized DFT calculations in a plane-wave basis using norm-conserving pseudopotentials (NCPs) or projector-augmented-wave (PAW) potentials to model the ions and core electrons, and density-dependent functionals from the LibXC library to describe exchange and correlation effects among valence electrons. In addition, NCP-based calculations can be performed using LibXC hybrid functionals, which combine density- and orbital-dependent (exact) exchange with density-dependent correlation. In this case, novel algorithms are used to construct and apply the exact-exchange operator, allowing the use of significantly more processing cores than are currently allowed with commercial and academic electronic structure codes. Socorro has state-of-the-art capabilities to: (1) relax the ionic coordinates in a simulation cell and optimize the cell size and shape, (2) run Born-Oppenheimer (molecular-dynamics) or Ehrenfest (time-dependent DFT plus ion dynamics) trajectories, and (3) identify transition states of migrating point defects. The input formats for lattice vectors and ion positions are similar to those used in commercial and academic codes and the keywords used to invoke capabilities are easily recognized, enabling short learning curves for experienced users of these codes. Based on experiences at Sandia's CINT (Center for Integrated Nano Technology) facility, the learning curve is also short for new users when they are mentored by an experienced user. The input format for PAW potentials is one of the formats provided by the AtomPAW code along with formats for the ABINIT and Quantum Espresso codes, thereby allowing Socorro users to generate PAW potentials from the ABINIT and Quantum Espresso PAW databases. In addition, Socorro can utilize PAW potentials from the Vanderbilt University OPAL project, which is developing highly optimized PAW potentials for specific atomic and electronic configurations and thereby yielding improved throughputs (by up to an order of magnitude) while maintaining accuracy.

Capability Bounds‎

Socorro outperforms commercial electronic-structure codes on various high-performance computing platforms.

Unique Aspects‎

Socorro is compatible with existing and near-term capability and capacity computing resources at Sandia, including an emerging capability to utilize OpenMP hardware threads and Intel threaded libraries. The code was designed to scale efficiently with the number of cores and exceeds the performance of popular commercial codes in capability class calculations, especially for hybrid-functional calculations.

Availability‎

Socorro is an open source code available under the terms of the Gnu Public License (GPL). It is available for download from Vanderbilt University.

Benefit‎

The Socorro code provides a robust capability for highly scalable DFT calculations.

Images

Thermal and carrier-induced migration processes of a neutral silicon interstitial in bulk silicon, obtained using Socorro. Bulk silicon atoms are represented with blue spheres. The silicon interstitial and bulk atoms with which it shares a bulk lattice site are represented with red spheres. The top row shows the thermal process, which involves a sequence of transitions between a ground state and a metastable state through a transition state with an energy 288 meV higher than that of the ground state. The bottom row shows the carrier-induced process, involving transitions through the tetrahedral ground state that are caused by alternating capture of holes and electrons.

Plot of the time spent constructing the exact exchange operator in Socorro self-consistent calculations for a 256-atom supercell of bulk gold (also shown) vs. the number of cores on a Cray XC40. The runs used one sampling point in the Brillouin zone and 2304 Kohn-Sham orbitals. The plot displays nearly ideal scaling (the diagonal line) from 2304 to 32x2304 = 73728 cores. For comparison, runs at Sandia for a 108-atom bulk gold supercell using a commercial plane-wave code scaled poorly beyond 128 cores.

References‎

Bounds on the range of density-functional-theory point defect levels in semiconductors and insulators, N.A. Modine, A.F. Wright, and S.R. Lee, Computational Materials Science 91, 431 (2014).
Application of the bounds-analysis approach to arsenic and gallium antisite defects in gallium arsenide, A.F. Wright and N.A. Modine, Physical Review B 91, 014110 (2015).
First-principles survey of the structure, formation energies, and transition levels of As-interstitial defects in InGaAs, S.R. Lee, A.F. Wright, N.A. Modine, C.C. Battaile, S.M. Foiles, J.C. Thomas, and A. Van der Ven, Physical Review B 92, 045205 (2015).
Force-based optimization of pseudopotentials for non-equilibrium configurations, C.N. Brock, B.C. Paikoff, M.I. Md Sallih, A.R. Tackett, and D.G. Walker, Computer Physics Communications 201, 106 (2016).
LibXC: www.tddft.org/programs/libxc
AtomPAW: http://users.wfu.edu/natalie/papers/pwpaw
Socorro: https://socorro.accre.vanderbilt.edu/