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4. Effect of Fe and Ni on the mechanical properties and deformation behavior of Co3Ti based alloys.

Author

Zhu, Xinghua, Fang, Yiheng, Feng, Qingguo, Wang, Ning, Xiao, Lei, and Xu, Yi

Subjects
DEFORMATIONS (Mechanics), STATIC equilibrium (Physics), ELECTRONIC structure, DUCTILITY, ALLOYS
Abstract

In this work, the effect of random substitution modes of Fe and Ni on the stability and mechanical properties of Co3Ti-based intermetallics was investigated using first principles calculations through occupancy modes, electronic structures, energies, and elastic constants. The results show that FeCo type substitution favors ductility while NiCo type substitution favors strength. Compared to the above two types of substitution, FeTi type substitution is favorable for obtaining a balance between stability and ductility, but it is not easy to achieve energetically. Synergy of three types of substitutions enables stability and equilibrium mechanical properties of Co3Ti-based multi-component intermetallics. In addition, the anti-site substitution of neighboring Co and Ti atoms interchanging their positions may be a key step in the formation of FeTi type substitutions in terms of energy. This work provides useful data and insights into the design and utilization of Co3Ti-based multi-component intermetallics. [ABSTRACT FROM AUTHOR]

Published
2024
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13. Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package

Author

Epifanovsky, Evgeny, Gilbert, Andrew TB, Feng, Xintian, Lee, Joonho, Mao, Yuezhi, Mardirossian, Narbe, Pokhilko, Pavel, White, Alec F, Coons, Marc P, Dempwolff, Adrian L, Gan, Zhengting, Hait, Diptarka, Horn, Paul R, Jacobson, Leif D, Kaliman, Ilya, Kussmann, Jörg, Lange, Adrian W, Lao, Ka Un, Levine, Daniel S, Liu, Jie, McKenzie, Simon C, Morrison, Adrian F, Nanda, Kaushik D, Plasser, Felix, Rehn, Dirk R, Vidal, Marta L, You, Zhi-Qiang, Zhu, Ying, Alam, Bushra, Albrecht, Benjamin J, Aldossary, Abdulrahman, Alguire, Ethan, Andersen, Josefine H, Athavale, Vishikh, Barton, Dennis, Begam, Khadiza, Behn, Andrew, Bellonzi, Nicole, Bernard, Yves A, Berquist, Eric J, Burton, Hugh GA, Carreras, Abel, Carter-Fenk, Kevin, Chakraborty, Romit, Chien, Alan D, Closser, Kristina D, Cofer-Shabica, Vale, Dasgupta, Saswata, de Wergifosse, Marc, Deng, Jia, Diedenhofen, Michael, Do, Hainam, Ehlert, Sebastian, Fang, Po-Tung, Fatehi, Shervin, Feng, Qingguo, Friedhoff, Triet, Gayvert, James, Ge, Qinghui, Gidofalvi, Gergely, Goldey, Matthew, Gomes, Joe, González-Espinoza, Cristina E, Gulania, Sahil, Gunina, Anastasia O, Hanson-Heine, Magnus WD, Harbach, Phillip HP, Hauser, Andreas, Herbst, Michael F, Vera, Mario Hernández, Hodecker, Manuel, Holden, Zachary C, Houck, Shannon, Huang, Xunkun, Hui, Kerwin, Huynh, Bang C, Ivanov, Maxim, Jász, Ádám, Ji, Hyunjun, Jiang, Hanjie, Kaduk, Benjamin, Kähler, Sven, Khistyaev, Kirill, Kim, Jaehoon, Kis, Gergely, Klunzinger, Phil, Koczor-Benda, Zsuzsanna, Koh, Joong Hoon, Kosenkov, Dimitri, Koulias, Laura, Kowalczyk, Tim, Krauter, Caroline M, Kue, Karl, Kunitsa, Alexander, Kus, Thomas, Ladjánszki, István, Landau, Arie, Lawler, Keith V, Lefrancois, Daniel, and Lehtola, Susi

Subjects
Physical Sciences, Chemical Sciences, Atomic, Molecular and Optical Physics, Physical Chemistry, Engineering, Chemical Physics, Chemical sciences, Physical sciences
Abstract

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear-electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an "open teamware" model and an increasingly modular design.

Published
2021

31. Enhanced properties of multi‐element soluted (Nb0.8Ti0.05Zr0.05Mo0.05M0.05)4AlC3 (M = Hf, Ta) ceramics.

Author

Soomro, Sumair Ahmed, Jahanger, Muhammad Irfan, Khan, Maaz Ullah, Zhou, Yanchun, Fu, Shuai, Wan, Detian, Bao, Yiwang, Feng, Qingguo, and Hu, Chunfeng

Subjects
SOLUTION strengthening, VICKERS hardness, SOLID solutions, FRACTURE toughness, FLEXURAL strength
Abstract

Recently multielements solid solution has shown significant improvement to the mechanical properties of parent MAX phases. Therefore, in this work, five elements with different radii were incorporated to check the effect on properties of MAX phases. (Nb0.8Ti0.05Zr0.05Mo0.05Hf0.05)4AlC3 (MAXHf) and (Nb0.8Ti0.05Zr0.05Mo0.05Ta0.05)4AlC3 (MAXTa) ceramics were successfully synthesized using the spark plasma sintering technique. The microstructure and elemental map analysis results further confirmed that the five transition metals were successfully solid soluted at the M‐sites of the hexagonal M4AlC3 unit cell. The mean elemental compositions for M‐site elements were achieved as Nb0.85Ti0.052Zr0.035Mo0.027Hf0.036 and Nb0.847Ti0.051Zr0.043Mo0.025Ta0.033 for MAXHf and MAXTa ceramics, respectively. The electrical and thermal conductivities of multielement solid solution MAX phases were decreased compared to pure Nb4AlC3. However, Mechanical properties were significantly increased with the solid solution of five transition metals. The fracture toughness, flexural strength, compressive strength and Vickers hardness (10 N) of MAXHf and MAXTa ceramics were achieved as 8.87 MPa m1/2, 448 MPa, 867 MPa, 6.5 GPa and 10.36 MPa m1/2, 557 MPa, 1039 MPa, 8.2 GPa, respectively. The enhanced mechanical properties suggest the effectiveness of the solid solution strengthening effect and provide new opportunities to further tailor the mechanical properties of the MAX phase ceramics. [ABSTRACT FROM AUTHOR]

Published
2024
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39. Inducing a Synergistic Effect on Ptδ+/Electron-Rich Sites via a Platinization Strategy: Generating Hyper-High Current Density in Hydrogen Evolution Reaction

Author

Wang, Shanshan, Zhao, Qin, Ma, Quanlei, Gan, Rong, Ran, Yiling, Fang, Weizhen, Wang, Cuijuan, Fang, Ling, Feng, Qingguo, Zhang, Yan, Wang, Dingsheng, and Li, Yadong

Abstract

Herein, we propose a platinization strategy for the preparation of Pt/X catalysts with low Pt content on substrates possessing electron-rich sites (Pt/X: X = Co3O4, NiO, CeO2, Covalent Organic Framework (COF), etc.). In examples with inorganic and organic substrates, respectively, Pt/Co3O4possesses remarkable catalytic ability toward HER, achieving a current density at an overpotential of 500 mV that is 3.22 times higher than that of commercial Pt/C. It was also confirmed by using operandoRaman spectroscopy that the enhancement of catalytic activity was achieved after platinization of the COF, with a reduction of overpotential from 231 to 23 mV at 10 mA cm–2. Density functional theory (DFT) reveals that the improved catalytic activity of Pt/Co3O4and Pt/COF originated from the re-modulation of Ptδ+on the electronic structure and the synergistic effect of the interfacial Ptδ+/electron-rich sites. This work provides a rapid synthesis strategy for the synthesis of low-content Pt catalysts for electrocatalytic hydrogen production.

Published
2024
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42. Synthesis of new rare earth containing MAX phases Sc2AC (A = Ga, In) by spark plasma sintering.

Author

Zhang, Qiqiang, Luo, Jia, Wen, Bo, Zhou, Yanchun, San, Xingyuan, Chen, Hui, Feng, Qingguo, and Hu, Chunfeng

Subjects
SINTERING, LATTICE constants, SCANNING electron microscopy, CRYSTAL structure, X-ray diffraction, RARE earth oxides
Abstract

In this paper, two new ternary layered MAX phase ceramics, Sc2GaC and Sc2InC, were successfully synthesized by spark plasma sintering. The crystal structures of two new compounds were determined by X‐ray diffraction. The lattice parameters were a = 3.3609(0) Å and c = 14.5849(9) Å for Sc2GaC, and a = 3.3453(6) Å and c = 15.2236(3) Å for Sc2InC, wherein the Sc atoms were located at (1/3, 2/3, 0.07330[Ga]/0.08268[In]), the A atoms were located at (1/3, 2/3, 3/4), and the C atoms were located at (0, 0, 0). Scanning electron microscopy images of two new MAX phase ceramics were also given in this paper, showing obvious layered characteristics. [ABSTRACT FROM AUTHOR]

Published
2024
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45. Green's functions and equations of motion in correlated many body systems

Author

Feng, Qingguo

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

In this paper some new physical notations are given for the Green's functions and equations of motion (EOM) in many body physics with the concept of quasiparticles. It shows how the many body correlations existing in many body systems can be taken into account through the derivation of EOMs self-consistently. The scheme is compared with the expansion of Feynman diagrams. Finally some further discussions are given for the unique properties of EOM techniques in helping to model a system and the interactions self-consistently.

Published
2013

47. Investigation of on-site inter-orbital single electron hoppings in general multi-orbital systems

Author

Feng, Qingguo and Oppeneer, Peter M.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity
Abstract

A general multi-orbital Hubbard model, which includes on-site inter-orbital electron hoppings, is introduced and studied. It is shown that the on-site inter-orbital single electron hopping is one of the most basic interactions. Two electron spin-flip and pair-hoppings are shown to be correlation effects of higher order than the on-site inter-orbital single hopping. It is shown how the double and higher hopping interactions can be well-defined for arbitrary systems. The two-orbital Hubbard model is studied numerically to demonstrate the influence of the single electron hopping effect, leading to a change of the shape of the bands and a shrinking of the difference between the two bands. Inclusion of the on-site inter-orbital hopping suppresses the so-called orbital-selective Mott transition., Comment: 5 pages, 3 figures

Published
2011
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48. Spin and orbital hybridization at specifically nested Fermi surfaces in URu$_2$Si$_2$

Author

Oppeneer, Peter M., Elgazzar, Saad, Rusz, Jan, Feng, Qingguo, Durakiewicz, Tomasz, and Mydosh, John A.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

The Fermi surface (FS) nesting properties of URu$_2$Si$_2$ are analyzed with particular focus on their implication for the mysterious hidden order phase. We show that there exist two Fermi surfaces that exhibit a strong nesting at the antiferromagnetic wavevector, $\boldsymbol{Q}_0$=(0,\,0,\,1). The corresponding energy dispersions fulfill the relation $\epsilon_{1}(\boldsymbol{k})$=$- \epsilon_{2} (\boldsymbol{k}\pm \boldsymbol{Q}_0)$ at eight FS hotspot lines. The spin-orbital characters of the involved $5f$ states are {\it distinct} ($j_z$=$\pm$5/2 {\it vs.} $\pm$3/2) and hence the degenerate Dirac crossings are symmetry protected in the nonmagnetic normal state. Dynamical symmetry breaking through an Ising-like spin and orbital excitation mode with $\Delta j_z$=$\pm$1 induces a hybridization of the two states, causing substantial FS gapping. Concomitant spin and orbital currents in the uranium planes give rise to a rotational symmetry breaking., Comment: 5 pages, 3 figures

Published
2011
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49. Advanced multi-orbital impurity solver for dynamical mean field theory based on the equation of motion approach

Author

Feng, Qingguo and Oppeneer, P. M.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We propose an improved fast multi-orbital impurity solver for the dynamical mean field theory (DMFT) based on equations of motion (EOM) of Green's functions and decoupling scheme. In this scheme the inter-orbital Coulomb interactions are treated fully self-consistently, involving the inter-orbital fluctuations. As an example of the derived multi-orbital impurity solver, the two-orbital Hubbard model is studied for various cases. Comparisons are made between numerical results obtained with our EOM scheme and those obtained with quantum Monte Carlo and numerical renormalization group methods. The comparison substantiates a good agreement, but also reveals a dissimilar behavior in the densities of states (DOS) which is caused by inter-site inter-orbital hopping effects and on-site inter-orbital fluctuation effects, thus corroborating the value of the EOM method for the study of multi-orbital strongly correlated systems., Comment: 14 pages, 9 figures

Published
2011
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50. Fast multi-orbital equation of motion impurity solver for dynamical mean field theory

Author

Feng, Qingguo and Oppeneer, P. M.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We propose a fast multi-orbital impurity solver for the dynamical mean field theory (DMFT). Our DMFT solver is based on the equations of motion (EOM) for local Green's functions and constructed by generalizing from the single-orbital case to the multi-orbital case with inclusion of the inter-orbital hybridizations and applying a mean field approximation to the inter-orbital Coulomb interactions. The two-orbital Hubbard model is studied using this impurity solver within a large range of parameters. The Mott metal-insulator transition and the quasiparticle peak are well described. A comparison of the EOM method with the QMC method is made for the two-orbital Hubbard model and a good agreement is obtained. The developed method hence holds promise as a fast DMFT impurity solver in studies of strongly correlated systems., Comment: 25 pages, 12 figures

Published
2011
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