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Pr2S2F is alpha Niobium phosphide-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Pr2S2F cluster. Pr is bonded in a linear geometry to one S and one F atom. The Pr–S bond length is 2.39 Å. The Pr–F bond length is 2.48 Å. S is bonded in a single-bond geometry to one Pr atom. F is bonded in a linear geometry to two equivalent Pr atoms.
La2OI2 crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one La2OI2 cluster. La2+ is bonded in a linear geometry to one O2- and one I1- atom. The La–O bond length is 2.11 Å. The La–I bond length is 2.98 Å. O2- is bonded in a linear geometry to two equivalent La2+ atoms. I1- is bonded in a single-bond geometry to one La2+ atom.
CuTl2Se2 crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one CuTl2Se2 cluster. Cu2+ is bonded in a linear geometry to two equivalent Se2- atoms. Both Cu–Se bond lengths are 2.22 Å. Tl1+ is bonded in a single-bond geometry to one Se2- atom. The Tl–Se bond length is 2.64 Å. Se2- is bonded in a linear geometry to one Cu2+ and one Tl1+ atom.
Rb2NaO2 is alpha Niobium phosphide-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Rb2NaO2 cluster. Rb is bonded in a single-bond geometry to one O atom. The Rb–O bond length is 2.35 Å. Na is bonded in a linear geometry to two equivalent O atoms. Both Na–O bond lengths are 2.18 Å. O is bonded in a linear geometry to one Rb and one Na atom.
Sr2I2F is Cyanogen Chloride-like structured and crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Sr2I2F cluster. Sr is bonded in a linear geometry to one I and one F atom. The Sr–I bond length is 2.94 Å. The Sr–F bond length is 2.30 Å. I is bonded in a single-bond geometry to one Sr atom. F is bonded in a linear geometry to two equivalent Sr atoms.
C14N8I3(I)3 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of two C14N8I3 clusters and two I clusters. In each C14N8I3 cluster, there are seven inequivalent C+2.14+ sites. In the first C+2.14+ site, C+2.14+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.59 Å. In the second C+2.14+ site, C+2.14+ is bonded in a distorted bent 150 degrees geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.39 Å) C–N bond length. In the third C+2.14+ site, C+2.14+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.47 Å. In the fourth C+2.14+ site, C+2.14+ is bonded in a distorted bent 120 degrees geometry to two N3- atoms. There is one shorter (1.32 Å) and one longer (1.39 Å) C–N bond length. In the fifth C+2.14+ site, C+2.14+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.20 Å. In the sixth C+2.14+ site, C+2.14+ is bonded in a distorted trigonal planar geometry to two N3- and one I1- atom. There is one shorter (1.29 Å) and one longer (1.36 Å) C–N bond length. The C–I bond length is 2.11 Å. In the seventh C+2.14+ site, C+2.14+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.19 Å. There are four inequivalent N3- sites. In the first N3- site, N3- is bonded in a linear geometry to two C+2.14+ atoms. In the second N3- site, N3- is bonded in a 3-coordinate geometry to three C+2.14+ atoms. In the third N3- site, N3- is bonded in a 2-coordinate geometry to three C+2.14+ atoms. In the fourth N3- site, N3- is bonded in a linear geometry to two C+2.14+ atoms. There are two inequivalent I1- sites. In the first I1- site, I1- is bonded in a linear geometry to two equivalent I1- atoms. Both I–I bond lengths are 3.55 Å. In the second I1- site, I1- is bonded in a single-bond geometry to one C+2.14+ and one I1- atom. In each I cluster, there are two inequivalent I1- sites. In the first I1- site, I1- is bonded in a linear geometry to two equivalent I1- atoms. Both I–I bond lengths are 2.88 Å. In the second I1- site, I1- is bonded in a distorted single-bond geometry to one I1- atom.
Yb2I2F is Cyanogen Chloride-like structured and crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Yb2I2F cluster. Yb is bonded in a linear geometry to one I and one F atom. The Yb–I bond length is 2.82 Å. The Yb–F bond length is 2.12 Å. I is bonded in a single-bond geometry to one Yb atom. F is bonded in a linear geometry to two equivalent Yb atoms.
Na2MnSb2 crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Na2MnSb2 cluster. Na1+ is bonded in a single-bond geometry to one Sb2- atom. The Na–Sb bond length is 2.97 Å. Mn2+ is bonded in a linear geometry to two equivalent Sb2- atoms. Both Mn–Sb bond lengths are 2.51 Å. Sb2- is bonded in a linear geometry to one Na1+ and one Mn2+ atom.
In preparation for the 2023 NSAC Long Range Plan (LRP), the DNP Town Meeting on Nuclear Structure, Reactions, and Astrophysics was held at Argonne National Laboratory (ANL) on Nov 14-16, 2022. The town meeting brought together 578 members of the low-energy nuclear science community, including 216 in-person attendees and 362 remote participants coming from US national laboratories, a wide range of US universities and other research institutions and universities abroad. Participants met in five topic-oriented and seven cross-cutting and intersecting working groups to discuss progress since the 2015 LRP and identify compelling science opportunities and the resources needed to realize them. These considerations were used during the Town Meeting to determine a set of resolutions outlining the highest priorities for our subfield. The full text of the resolutions endorsed by unanimous consent by the low-energy nuclear science community at the Town Meeting is presented at the end of this executive summary. The reports from all working groups that met during the Town Meeting are included as Secs. 1 to 11 of this Whitepaper. The intellectual challenges for nuclear structure, reactions and astrophysics can be captured in the following questions: What is the nature of the nuclear force that binds protons and neutrons into stable nuclei and rare isotopes, and how do the rich phenomena of nuclear structure and reactions emerge? How do single-nucleon, cluster, and collective degrees of freedom coexist and evolve with increasing proton-neutron imbalance and excitation energies? What are the limits of nuclear existence, and what features arise near and beyond these limits? What are the astrophysical origins of the elements and how did the associated chemical evolution proceed? How do stars evolve, and what nuclear signatures do they leave behind? What is the nature of neutron stars and dense matter? How can the knowledge and technological progress provided by nuclear science best be used to benefit society?
We present an optimized Floyd-Warshall (Floyd-Warshall) algorithm that computes the All-pairs shortest path (APSP) for GPU accelerated clusters. The Floyd-Warshall algorithm due to its structural similarities to matrix-multiplication is well suited for highly parallel GPU architectures. To achieve high parallel efficiency, we address two key algorithmic challenges: reducing high communication overhead and addressing limited GPU memory. To reduce high communication costs, we redesign the parallel (a) to expose more parallelism, (b) aggressively overlap communication and computation with pipelined and asynchronous scheduling of operations, and (c) tailored MPI-collective. To cope with limited GPU memory, we employ an offload model, where the data resides on the host and is transferred to GPU on-demand. The proposed optimizations are supported with detailed performance models for tuning. Our optimized parallel Floyd-Warshall implementation is up to 5x faster than a strong baseline and achieves 8.1 PetaFLOPS/sec on 256~nodes of the Summit supercomputer at Oak Ridge National Laboratory. This performance represents 70% of the theoretical peak and 80% parallel efficiency. The offload algorithm can handle 2.5x larger graphs with a 20% increase in overall running time.
Li2PtH2 is alpha Niobium phosphide-derived structured and crystallizes in the orthorhombic Immm space group. The structure is zero-dimensional and consists of two Li2PtH2 clusters. Li1+ is bonded in a 1-coordinate geometry to one H atom. The Li–H bond length is 1.97 Å. Pt2- is bonded in a distorted linear geometry to two equivalent H atoms. Both Pt–H bond lengths are 1.67 Å. H is bonded in a distorted linear geometry to one Li1+ and one Pt2- atom.
Np2OI2 is Cyanogen Chloride-like structured and crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Np2OI2 cluster. Np is bonded in a distorted linear geometry to one O and one I atom. The Np–O bond length is 2.06 Å. The Np–I bond length is 2.89 Å. O is bonded in a linear geometry to two equivalent Np atoms. I is bonded in a single-bond geometry to one Np atom.
Pu2OI2 is Cyanogen Chloride-like structured and crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Pu2OI2 cluster. Pu is bonded in a distorted linear geometry to one O and one I atom. The Pu–O bond length is 2.02 Å. The Pu–I bond length is 2.85 Å. O is bonded in a linear geometry to two equivalent Pu atoms. I is bonded in a single-bond geometry to one Pu atom.
Tl2SI2 is alpha Niobium phosphide-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Tl2SI2 cluster. Tl2+ is bonded in a linear geometry to one S2- and one I1- atom. The Tl–S bond length is 2.50 Å. The Tl–I bond length is 2.89 Å. S2- is bonded in a linear geometry to two equivalent Tl2+ atoms. I1- is bonded in a distorted single-bond geometry to one Tl2+ atom.
Na2MnP2 crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Na2MnP2 cluster. Na1+ is bonded in a distorted single-bond geometry to one P2- atom. The Na–P bond length is 2.77 Å. Mn2+ is bonded in a linear geometry to two equivalent P2- atoms. Both Mn–P bond lengths are 2.19 Å. P2- is bonded in a linear geometry to one Na1+ and one Mn2+ atom.
Lu2OI2 is Cyanogen Chloride-like structured and crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Lu2OI2 cluster. Lu is bonded in a distorted linear geometry to one O and one I atom. The Lu–O bond length is 1.99 Å. The Lu–I bond length is 2.79 Å. O is bonded in a linear geometry to two equivalent Lu atoms. I is bonded in a single-bond geometry to one Lu atom.
Tm2OI2 is Cyanogen Chloride-like structured and crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Tm2OI2 cluster. Tm is bonded in a distorted linear geometry to one O and one I atom. The Tm–O bond length is 2.01 Å. The Tm–I bond length is 2.81 Å. O is bonded in a linear geometry to two equivalent Tm atoms. I is bonded in a single-bond geometry to one Tm atom.
Er2OI2 is Cyanogen Chloride-like structured and crystallizes in the tetragonal P4/mmm space group. The structure is zero-dimensional and consists of one Er2OI2 cluster. Er is bonded in a distorted linear geometry to one O and one I atom. The Er–O bond length is 2.03 Å. The Er–I bond length is 2.82 Å. O is bonded in a linear geometry to two equivalent Er atoms. I is bonded in a single-bond geometry to one Er atom.