Block2: a comprehensive open source framework to develop and apply state-of-the-art DMRG algorithms in electronic structure and beyond

Block2 is an open source framework to implement and perform density matrix renormalization group and matrix product state algorithms. Out-of-the-box it supports the eigenstate, time-dependent, response, and finite-temperature algorithms. In addition, it carries special optimizations for ab initio electronic structure Hamiltonians and implements many quantum chemistry extensions to the density matrix renormalization group, such as dynamical correlation theories. The code is designed with an emphasis on flexibility, extensibility, and efficiency, and to support integration with external numerical packages. Here we explain the design principles and currently supported features and present numerical examples in a range of applications.Comment: 20 pages, 8 figure

Minimum-acceleration local modification method for planning tool orientations in 5-axis ball-end machining

In 5-axis CNC machining, it is important to avoid drastic changes of tool orientations for improving kinematics performances of two rotary axes of 5-axis machine tools and achieving good machining surface quality. For this purpose, in this paper, a minimum-acceleration local modification (MALM) method is proposed to plan the tool orientations for 5-axis ball-end machining. First, with several specified representative tool orientations (RTOs), initial tool orientations are generated efficiently along the tool path by quaternion interpolation (QI) method while guaranteeing no machining interferences. Then, the generated tool orientations are checked whether the angular accelerations of the rotary axes exceed their drive limits, and the over-limit areas (OLAs), which are involved in tool orientation modification, are subsequently identified. In the OLAs, the minimum-acceleration model for local modification of tool orientations is given in machine coordinate system (MCS), and then is used to adjust the tool orientations to improve the kinematics performance of the rotary axes. Finally, the experiments demonstrated that this method can improve significantly the kinematics performances of the rotary axes

Dissolution of M23C6 and New Phase Re-Precipitation in Fe Ion-Irradiated RAFM Steel

The M23C6 precipitate plays a major role in preventing the sliding of the grain boundary and strengthens the matrix in the reduced-activation ferritic/martensic (RAFM) steel. However, its stability might be reduced under irradiation. The microstructural instability of the M23C6 precipitates in the RAFM steels irradiated at 300 °C with Fe ions up to a peak dose of 40 dpa was investigated by transmission electron microscopy. A “Core/Shell” morphology was found for the pre-existing M23C6 and a large number of new small phases appeared in parallel near the periphery of the precipitates after irradiation. The loss of crystallinity of the M23C6 periphery due to the dissolution of carbon atoms into the interface (C-rich “Shell”) actually decreased the size of the Cr-rich “Core”. The new phase that formed around the pre-existing precipitates was M6C (Fe3W3C), which was formed through the carbide transformation of M23C6 to M6C

Characteristics of Solar Wind Radiation Damage in Lunar Soil: PAT and TEM Study

Irradiation structural damage (e.g., radiation tracks, amorphous layers, and vesicles) is widely observed in lunar soil grains. Previous experiments have revealed that irradiation damage is caused by the injection of solar wind and solar flare energetic particles. In this study, cordierite and gabbro were selected as analogs of shallow and deep excavated lunar crust materials for proton irradiation experiments. The fluence was 1.44 ± 0.03 × 1018 H+/cm2, which is equivalent to 102 years of average solar wind proton implantation on the Moon. Before and after irradiation, structural damage in samples is detected by slow positron annihilation technology (PAT), Doppler broadening (DB) measurement, focused ion beam (FIB), and transmission electron microscopy (TEM). The DB results showed the structural damage peaks of irradiated gabbro and cordierite were located at 40 and 45 nm. Hydrogen diffused to a deeper region and it reached beyond depths of 150 and 136 nm for gabbro and cordierite, respectively. Hydrogen atoms occupied the original vacancy defects and formed vacancy sites—hydrogen atom complexes, which affected the annihilation of positrons with electrons in the vacancy defects. All of the DB results were validated by TEM. This study proves that the positron annihilation technique has an excellent performance in the detection of defects in the whole structure of the sample. In combination with TEM and other detection methods, this technology could be used for the detection of structural damage in extraterrestrial samples

Effect of Vacancy Behavior on Precipitate Formation in a Reduced-Activation V−Cr−Mn Medium-Entropy Alloy

In this work, we studied the evolution of vacancy-like defects and the formation of brittle precipitates in a reduced-activation V−Cr−Mn medium-entropy alloy. The evolution of local electronic circumstances around Cr and Mn enrichments, the vacancy defects, and the CrMn3 precipitates were characterized by using scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, and positron annihilation spectroscopy. The microstructure measurements showed that the Mn and Cr enrichments in the as-cast sample significantly evolved with temperature, i.e., from 400 °C, the Cr/Mn-segregated regions gradually dissolved into the matrix and then disappeared, and from 900 °C to 1000 °C, they existed as CrMn3 precipitates. The crystallite size of the phase corresponding to CrMn3 precipitates was about 29.4 nm at 900 °C and 43.7 nm at 1000 °C. The positron annihilation lifetime results demonstrated that the vacancies mediated the migration of Cr and Mn, and Cr and Mn segregation finally led to the formation of CrMn3 precipitates. The coincidence Doppler broadening results showed that the characteristic peak moved to the low-momentum direction, due to an increase in the size of the vacancy defects at the interface and the formation of CrMn3 precipitates