Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

비만아 부모의 돌봄 경험: q 방법론

Magnetism, originating from the moving charges and spin of elementary particles, has revolutionized important technologies such as data storage and biomedical imaging, and continues to bring forth new phenomena in emergent materials and reduced dimensions. The recently discovered two-dimensional (2D) magnetic van der Waals crystals provide ideal platforms for understanding 2D magnetism, the control of which has been fueling opportunities for atomically thin, flexible magneto-optic and magnetoelectric devices (such as magnetoresistive memories and spin field-effect transistors). The seamless integration of 2D magnets with dissimilar electronic and photonic materials opens up exciting possibilities for unprecedented properties and functionalities. We review the progress in this area and identify the possible directions for device applications, which may lead to advances in spintronics, sensors, and computing.

Two-dimensional magnetic crystals and emergent heterostructure devices

Materials research has driven the development of modern nano-electronic devices. In particular, research in magnetic thin films has revolutionized the development of spintronic devices1,2 because identifying new magnetic materials is key to better device performance and design. Van der Waals crystals retain their chemical stability and structural integrity down to the monolayer and, being atomically thin, are readily tuned by various kinds of gate modulation3,4. Recent experiments have demonstrated that it is possible to obtain two-dimensional ferromagnetic order in insulating Cr2Ge2Te6 (ref. 5) and CrI3 (ref. 6) at low temperatures. Here we develop a device fabrication technique and isolate monolayers from the layered metallic magnet Fe3GeTe2 to study magnetotransport. We find that the itinerant ferromagnetism persists in Fe3GeTe2 down to the monolayer with an out-of-plane magnetocrystalline anisotropy. The ferromagnetic transition temperature, Tc, is suppressed relative to the bulk Tc of 205 kelvin in pristine Fe3GeTe2 thin flakes. An ionic gate, however, raises Tc to room temperature, much higher than the bulk Tc. The gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2 opens up opportunities for potential voltage-controlled magnetoelectronics7-11 based on atomically thin van der Waals crystals.

Gate-tunable Room-temperature Ferromagnetism in Two-dimensional Fe 3 GeTe 2

Interlayer magnetic interactions between two-dimension van der Waals layers are often thought to be weak or even negligible and their mechanism is largely unexplored. Here, the authors propose a mechanism for these interactions in a CrI${}_{3}$ bilayer, based on the concept of covalent-like quasibonding, which offers significant alteration of interlayer wave-function hybridization but small energetic difference between different stacking configurations. While a near-collinear coupling between two parallel spin-polarized I 5$p$ orbitals prefers interlayer ferromagnetism, a noncollinear one favors antiferromagnetism, which is tunable by surmounting a tiny energy barrier between two stacking orders. This explains experimental observations and suggests a strategy for designing interlayer magnetism.

Stacking tunable interlayer magnetism in bilayer CrI 3

Manipulating physical properties using the spin degree of freedom constitutes a major part of modern condensed matter physics and is a key aspect for spintronics devices. Using the newly discovered two-dimensional van der Waals ferromagnetic CrI3 as a prototype material, we theoretically demonstrated a giant magneto band-structure (GMB) effect whereby a change of magnetization direction significantly modifies the electronic band structure. Our density functional theory calculations and model analysis reveal that rotating the magnetic moment of CrI3 from out-of-plane to in-plane causes a direct-to-indirect bandgap transition, inducing a magnetic field controlled photoluminescence. Moreover, our results show a significant change of Fermi surface with different magnetization directions, giving rise to giant anisotropic magnetoresistance. Additionally, the spin reorientation is found to modify the topological states. Given that a variety of properties are determined by band structures, our predicted GMB effec...

Spin Direction-Controlled Electronic Band Structure in Two-Dimensional Ferromagnetic CrI3.

The discovery of infinite-layer nickelate superconductor marks the new era in the field of superconductivity. In the rare-earth ($R$) nickelates $\mathrm{RNi}{\mathrm{O}}_{2}$, although the Ni is also of ${d}^{9}$ electronic configuration, analogous to Cu ${d}^{9}$ in cuprates, whether electronic structures in infinite-layer nickelate are the same as cuprate and possess the single-band feature as well are still open questions. To illustrate the electronic structure of rare-earth infinite-layer nickelate, we perform first-principles calculations of $\mathrm{LaNi}{\mathrm{O}}_{2}$ and $\mathrm{NdNi}{\mathrm{O}}_{2}$ compounds and compare them with that of $\mathrm{CaCu}{\mathrm{O}}_{2}$ using the hybrid functional method together with Wannier projection and group symmetry analysis. Our results indicate that the Ni ${{d}_{{x}^{2}}}_{\ensuremath{-}{y}^{2}}$ in the $\mathrm{LaNi}{\mathrm{O}}_{2}$ has weak hybridization with other orbitals and exhibits the characteristic single-band feature, whereas in $\mathrm{NdNi}{\mathrm{O}}_{2}$, the Nd $f$ orbital hybridizes with Ni ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and is a non-negligible ingredient for transport and even high-temperature superconductivity. Given that the Cu ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ in cuprate strongly hybridizes with O $2p$, the calculated band structures of nickelate imply some new band characters, which is worthy of more attention.

P. H. Jiang

Papers

Stacking tunable interlayer magnetism in bilayer CrI 3

Spin Direction-Controlled Electronic Band Structure in Two-Dimensional Ferromagnetic CrI3.

Electronic structure of rare-earth infinite-layer R Ni O 2 ( R = La , Nd )

Graphdiyne: A two-dimensional thermoelectric material with high figure of merit

Phase Manipulating toward Molybdenum Disulfide for Optimizing Electromagnetic Wave Absorbing in Gigahertz