There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Random graphs

Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software

/pdf/advanced-capabilities-for-materials-modelling-with-quantum-40poaosrve.pdf

Advanced capabilities for materials modelling with Quantum ESPRESSO.

https://par.nsf.gov/servlets/purl/10107309

ShengBTE: A solver of the Boltzmann transport equation for phonons ☆

BoltzTraP2, a program for interpolating band structures and calculating semi-classical transport coefficients

A rigorous first principles Boltzmann-Peierls equation (BPE) for phonon transport approach is employed to examine the lattice thermal conductivity, ${\ensuremath{\kappa}}_{L}$, of strained and unstrained graphene. First principles calculations show that the out-of-plane, flexural acoustic phonons provide the dominant contribution to ${\ensuremath{\kappa}}_{L}$ of graphene for all strains, temperatures, and system sizes considered, supporting a previous prediction that used an optimized Tersoff empirical interatomic potential. For the range of finite system sizes considered, we show that the ${\ensuremath{\kappa}}_{L}$ of graphene is relatively insensitive to strain. This provides validation for use of the BPE approach to calculate ${\ensuremath{\kappa}}_{L}$ for unstrained graphene, which has recently been called into question. The temperature and system size dependence of the calculated ${\ensuremath{\kappa}}_{L}$ of graphene is in good agreement with experimental data. The enhancement of ${\ensuremath{\kappa}}_{L}$ with isotopic purification is found to be relatively small due to strong anharmonic phonon-phonon scattering. This work provides insight into the nature of phonon thermal transport in graphene, and it demonstrates the power of first principles thermal transport techniques.

Phonon thermal transport in strained and unstrained graphene from first principles

Experimentally determining the lattice thermal conductivity of materials with very high or low values is expensive and time consuming. An efficient computational approach using machine-learning techniques finds a much larger range of conductivity than expected for an impressive number of half-Heusler compounds and also offers a way to rapidly evaluate other classes of materials.

Finding Unprecedentedly Low-Thermal-Conductivity Half-Heusler Semiconductors via High-Throughput Materials Modeling

Using ab initio calculations, we have investigated the phonon linewidths and the thermal conductivity (κ) of monolayer MoS2. κ for a typical sample size of 1 μm is 83 W/m K at room temperature in the completely rough edge limit, suggesting κ is not a limiting factor for the electronic application of monolayer MoS2. κ can be further increased by 30% in 10 μm sized samples. Due to strong anharmonicity, isotope enhancement of room temperature κ is only 10% for 1 μm sized samples. However, linewidths can be significantly reduced, for instance, for Raman active modes A1g and E2g1, in isotopically pure samples.

Jesús Carrete

Papers

ShengBTE: A solver of the Boltzmann transport equation for phonons ☆

BoltzTraP2, a program for interpolating band structures and calculating semi-classical transport coefficients

Phonon thermal transport in strained and unstrained graphene from first principles

Finding Unprecedentedly Low-Thermal-Conductivity Half-Heusler Semiconductors via High-Throughput Materials Modeling

Thermal conductivity and phonon linewidths of monolayer MoS2 from first principles