Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set

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

QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

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QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials

We present ab initio quantum-mechanical molecular-dynamics simulations of the liquid-metal--amorphous-semiconductor transition in Ge. Our simulations are based on (a) finite-temperature density-functional theory of the one-electron states, (b) exact energy minimization and hence calculation of the exact Hellmann-Feynman forces after each molecular-dynamics step using preconditioned conjugate-gradient techniques, (c) accurate nonlocal pseudopotentials, and (d) Nos\'e dynamics for generating a canonical ensemble. This method gives perfect control of the adiabaticity of the electron-ion ensemble and allows us to perform simulations over more than 30 ps. The computer-generated ensemble describes the structural, dynamic, and electronic properties of liquid and amorphous Ge in very good agreement with experiment. The simulation allows us to study in detail the changes in the structure-property relationship through the metal-semiconductor transition. We report a detailed analysis of the local structural properties and their changes induced by an annealing process. The geometrical, bonding, and spectral properties of defects in the disordered tetrahedral network are investigated and compared with experiment.

Ab initio molecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium.

Erratum: Spontaneous formation of stress domains on crystal surfaces [Phys. Rev. Lett. 61, 1973 (1988)]

Zintl phases, containing strongly covalently bonded frameworks with separate ionically bonded ions, have emerged as a critical materials family in which to couple magnetism and strong spin-orbit coupling to drive diverse topological phases of matter. Here we report the single-crystal synthesis, magnetic, thermodynamic, transport, and theoretical properties of the Zintl compound ${\mathrm{EuZn}}_{2}{\mathrm{P}}_{2}$ that crystallizes in the anti-${\mathrm{La}}_{2}{\mathrm{O}}_{3}$ (${\mathrm{CaAl}}_{2}{\mathrm{Si}}_{2}$) P-$3m1$ structure, containing triangular layers of ${\mathrm{Eu}}^{2+}$ ions. In-plane resistivity measurements reveal insulating behavior with an estimated activation energy of ${E}_{g}=0.11\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. Specific heat and magnetization measurements indicate antiferromagnetic ordering at ${T}_{N}=23\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Curie-Weiss analysis of in-plane and out of plane magnetic susceptibility from $T=150$ to 300 K yields ${p}_{\mathrm{eff}}=8.61$ for ${\ensuremath{\mu}}_{0}H\ensuremath{\perp}c$ and ${p}_{\mathrm{eff}}=7.74$ for ${\ensuremath{\mu}}_{0}H//c$, close to the expected values for the $4{f}^{7} J=S=7/2 {\mathrm{Eu}}^{2+}$ ion and indicative of weak anisotropy. Below ${T}_{N}$, a significant anisotropy of ${\ensuremath{\chi}}_{\ensuremath{\perp}}/{\ensuremath{\chi}}_{//}\ensuremath{\approx}2.3$ develops, consistent with $A$-type magnetic order as observed in isostructural analogs and as predicted by the density functional theory calculations reported herein. The positive Weiss temperatures of ${\ensuremath{\theta}}_{W}=19.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for ${\ensuremath{\mu}}_{0}H\ensuremath{\perp}c$ and ${\ensuremath{\theta}}_{W}=41.9\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for ${\ensuremath{\mu}}_{0}H//c$ show a similar anisotropy and suggest competing ferromagnetic and antiferromagnetic interactions. Comparing Eu magnetic ordering temperatures across trigonal $\mathrm{Eu}{M}_{2}{X}_{2}$ ($M=$ divalent metal, $X=$ pnictide) shows that ${\mathrm{EuZn}}_{2}{\mathrm{P}}_{2}$ exhibits the highest ordering temperature, with variations in ${T}_{N}$ correlating with changes in expected dipolar interaction strengths within and between layers and independent of the magnitude of electrical conductivity. These results provide experimental validation of the crystochemical intuition that the cation ${\mathrm{Eu}}^{2+}$ layers and the anionic ${({M}_{2}{X}_{2})}^{2--}$ framework can be treated as electronically distinct subunits, enabling further predictive materials design. 

/pdf/mml-math-xmlns-mml-http-www-w3-org-1998-math-mathml-mml-mi-a-1urnkmgp.pdf

<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>A</mml:mi></mml:math>
-type antiferromagnetic order in the Zintl-phase insulator 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>EuZn</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvari

Engineering Weyl phases and nonlinear Hall effects in T d -MoTe 2

Tomáš Rauch, Thomas Olsen, David Vanderbilt, and Ivo Souza 5 Friedrich-Schiller-University Jena, 07743 Jena, Germany Computational Atomic-scale Materials Design, Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby Denmark Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854-8019, USA Centro de F́ısica de Materiales, Universidad del Páıs Vasco, 20018 San Sebastián, Spain Ikerbasque Foundation, 48013 Bilbao, Spain

Mirror Chern number in the hybrid Wannier representation

We extend the recently-developed theory of bulk orbital magnetization to finite electric fields, and use it to calculate the orbital magnetoelectric response of periodic insulators. Working in the independent-particle framework, we find that the finite-field orbital magnetization can be written as a sum of three gauge-invariant contributions, one of which has no counterpart at zero field. The extra contribution is collinear with and explicitly dependent on the electric field. The expression for the orbital magnetization is suitable for first-principles implementations, allowing to calculate the magnetoelectric response coefficients by numerical differentiation. Alternatively, perturbation-theory techniques may be used, and for that purpose we derive an expression directly for the linear magnetoelectric tensor by taking the first field-derivative analytically. Two types of terms are obtained. One, the `Chern-Simons' term, depends only on the unperturbed occupied orbitals and is purely isotropic. The other, `Kubo' term, involves the first-order change in the orbitals and gives isotropic as well as anisotropic contributions to the response. In ordinary magnetoelectric insulators both terms are generally present, while in strong Z2 topological insulators only the former type is allowed, and is quantized. In order to validate the theory we have calculated under periodic boundary conditions the linear magnetoelectric coupling for a 3-D tight-binding model of an ordinary magnetoelectric insulator, using both the finite-field and perturbation-theory expressions. The results are in excellent agreement with calculations on bounded samples.

David Vanderbilt

Papers

Erratum: Spontaneous formation of stress domains on crystal surfaces [Phys. Rev. Lett. 61, 1973 (1988)]

<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>A</mml:mi></mml:math> -type antiferromagnetic order in the Zintl-phase insulator <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>EuZn</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvari

Engineering Weyl phases and nonlinear Hall effects in T d -MoTe 2

Mirror Chern number in the hybrid Wannier representation

Theory of orbital magnetoelectric response