Yongchao Liang

Bio: Yongchao Liang is an academic researcher from Guizhou University. The author has contributed to research in topics: Materials science & Crystallization. The author has an hindex of 8, co-authored 40 publications receiving 185 citations. Previous affiliations of Yongchao Liang include Hunan University.

Structural evolutions and hereditary characteristics of icosahedral nano-clusters formed in Mg 70 Zn 30 alloys during rapid solidification processes

Abstract: To investigate the structural evolution and hereditary mechanism of icosahedral nano-clusters formed during rapid solidification, a molecular dynamics (MD) simulation study has been performed for a system consisting of 107 atoms of liquid Mg70Zn30 alloy. Adopting Honeycutt-Anderson (HA) bond-type index method and cluster type index method (CTIM-3) to analyse the microstructures in the system it is found that for all the nano-clusters including 2~8 icosahedral clusters in the system, there are 62 kinds of geometrical structures, and those can be classified, by the configurations of the central atoms of basic clusters they contained, into four types: chain-like, triangle-tailed, quadrilateral-tailed and pyramidal-tailed. The evolution of icosahedral nano-clusters can be conducted by perfect heredity and replacement heredity, and the perfect heredity emerges when temperature is slightly less than Tm then increase rapidly and far exceeds the replacement heredity at Tg; while for the replacement heredity, there are three major modes: replaced by triangle (3-atoms), quadrangle (4-atoms) and pentagonal pyramid (6-atoms), rather than by single atom step by step during rapid solidification processes.

The connection of icosahedral and defective icosahedral clusters in medium-range order structures of CuZrAl alloy

Abstract: Medium-range order structure is the one of the important local structural units in the field of bulk metallic glasses. The rapid solidification of Cu50Zr40Al10 ternary alloy is investigated by molecular dynamics simulation. Simultaneously, the connections between the full icosahedral and defective icosahedral clusters in medium-range order structures of Cu50Zr40Al10 alloy are characterized systematically by the quantitative method and visualization analysis. The results reveal that the icosahedral clusters as the main structures with high structural stability are bonded with each other by interpenetrating connection, and form the triangle, double triangle, triple triangle, tetrahedron and chain connected icosahedral medium-range order clusters. Moreover, the icosahedral and defective icosahedral clusters prefer to link with each other and form the bigger medium-range order clusters with different configurations in this system. These structures keep the high structural stability of icosahedral medium-range order section and the structural variability of chain-like medium-range order structures.

Fast parallel algorithms for short-range molecular dynamics

Abstract: 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.

Monolayer II-VI semiconductors: A first-principles prediction

Abstract: Hui Zheng,1 Xian-Bin Li,1,* Nian-Ke Chen,1 Sheng-Yi Xie,1 Wei Quan Tian,1,2 Yuanping Chen,3 Hong Xia,1 S. B. Zhang,1,4,† and Hong-Bo Sun1,‡ 1State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China 2Institute of Theoretical Chemistry, Jilin University, Changchun 130012, China 3Laboratory for Quantum Engineering and Micro-Nano Energy Technology, Xiangtan University, Xiangtan 411105, China 4Department of Physics, Applied Physics, & Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, USA (Received 11 January 2015; revised manuscript received 14 May 2015; published 21 September 2015)

A Hybrid Density Functional Study of Armchair SiC Nanotubes

Abstract: First-principles calculations for the electronic and geometric structures of three different types of armchair silicon carbide nanotubes from (3, 3) to (11, 11) have been performed using hybrid density functional theory and the finite cluster approximation. Full geometry and spin optimizations have been performed without any symmetry constraints. A detailed comparison of the structures and stabilities of the three types of nanotubes is presented. For type 1 nanotube, the cohesive energy appears to saturate at $4.63\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, whereas for type 2 and 3 nanotubes, the cohesive energy saturates at approximately $4.44\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The dependence of the electronic band gaps on the respective tube diameters, energy density of states, and dipole moments as well as Mulliken charge distributions have been investigated. For type 1 nanotubes, Si atoms moved toward the tube axis and C atoms moved in the opposite direction after relaxation, consistent with other SiC nanotubes found in literature. For type 2 and the newly proposed type 3, this displacement direction is reversed. The band gaps for type 1 nanotubes are larger than bulk $3C\text{\ensuremath{-}}\mathrm{Si}\mathrm{C}$ gap, varying between 2.78 and $2.91\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, while type 2 and type 3 nanotubes have significantly lower band gaps. Unlike the other two types, band gap for type 3 nanotubes decreases monotonically with increasing tube diameter from $1.22\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for the smallest tube to $0.79\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for the largest (11, 11) tube studied here. The corresponding numbers for type 2 are 1.49 and $0.91\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ with an oscillatory pattern. None of the tubes appear to be magnetic. It is expected that these tubes will have interesting and important applications in the field of band gap engineering and molecular electronics.

Rational Design and Spontaneous Sulfurization of NiCo‐(oxy)Hydroxysulfides Nanosheets with Modulated Local Electronic Configuration for Enhancing Oxygen Electrocatalysis

Abstract: Transition metal chalcogenides (TMCs) have been identified as pre‐electrocatalysts for the oxygen evolution reaction (OER) and the high valent TMs in the in situ generated oxyhydroxides are considered to be the real OER catalytic center. However, the role of chalcogens for OER process has been ignored and not fully elucidated. Herein, it is discovered that about 2.8–3.5% of chalcogens remain in as oxidized derivatives at a steady state, which plays a vital role for enhancing the catalytic activity. A facile and spontaneous sulfurizing method is developed to synthesize sulfur‐doped NiCo‐(oxy)hydroxysulfides (NCOSH) nanosheets, in which the sulfur can directly bond with high‐valence TMs and keep them stable for OER catalysis. Theoretical and experimental results suggest that the S‐coordination in NCOSH can cause bond length strengthening and electronic modulation between TM‐S and TM‐O, thus enhancing the oxidation activity and stability of high‐valence TMs in NCOSH. Consequently, the as‐obtained NCOSH exhibits superior bifunctional activities and durability for oxygen electrocatalytic reactions, and also serves as a superb air cathode in rechargeable solid state Zn‐air batteries. This work sheds light on the rational design of (oxy)hydroxysulfides as efficient electrocatalysts and gains deeper fundamental insights on the enhancing mechanism of S in oxyhydroxysulfides for diverse electrochemical applications.