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Danny L Yeager - One of the best experts on this subject based on the ideXlab platform.

  • The complex-scaled multiconfigurational Spin-Tensor electron propagator method for low-lying shape resonances in Be−, Mg− and Ca−
    Chemical Physics, 2017
    Co-Authors: Tsednee Tsogbayar, Danny L Yeager
    Abstract:

    Abstract We further apply the complex scaled multiconfigurational Spin-Tensor electron propagator method (CMCSTEP) for the theoretical determination of resonance parameters with electron-atom systems including open-shell and highly correlated (non-dynamical correlation) atoms and molecules. The multiconfigurational Spin-Tensor electron propagator method (MCSTEP) developed and implemented by Yeager and his coworkers for real space gives very accurate and reliable ionization potentials and electron affinities. CMCSTEP uses a complex scaled multiconfigurational self-consistent field (CMCSCF) state as an initial state along with a dilated Hamiltonian where all of the electronic coordinates are scaled by a complex factor. CMCSTEP is designed for determining resonances. We apply CMCSTEP to get the lowest 2 P (Be − , Mg − ) and 2 D (Mg − , Ca − ) shape resonances using several different basis sets each with several complete active spaces. Many of these basis sets we employ have been used by others with different methods. Hence, we can directly compare results with different methods but using the same basis sets.

  • Electron-atom scattering resonances: Complex-scaled multiconfigurational Spin-Tensor electron propagator method for B − shape resonances
    Physical Review A, 2015
    Co-Authors: Tsogbayar Tsednee, Danny L Yeager
    Abstract:

    We develop the complex-scaled multiconfigurational Spin-Tensor electron propagator (CMCSTEP) technique for the theoretical determination of resonance parameters with electron-atom--molecule systems including open-shell and highly correlated (nondynamical correlation) atoms and molecules. The multiconfigurational Spin-Tensor electron propagator method developed and implemented by Yeager and his coworkers in real space gives very accurate and reliable ionization potentials and electron affinities. The CMCSTEP method uses a complex-scaled multiconfigurational self-consistent field state as an initial state along with a dilated Hamiltonian where all of the electronic coordinates are scaled by a complex factor. We apply the CMCSTEP and the related ${\text{M}}_{1}$ methods to get the ${\text{B}}^{\ensuremath{-}}$ shape resonance parameters using $14s11p$ and $14s11p5d$ basis sets with $1s2s2p3s$, $1s2s2p3s3p$, $1s2s2p3d$, $2s2p3s3p$, $2s2p3d$, and $2s2p3s3p3d$ complete active spaces. The CMCSTEP and ${\text{M}}_{1}$ resonance positions and widths are obtained for the $1{s}^{2}2{s}^{2}2{p}^{2}{\phantom{\rule{0.16em}{0ex}}}^{1}D$, $1{s}^{2}2s2{p}^{3}{\phantom{\rule{0.16em}{0ex}}}^{3}D$, and $1s2{s}^{2}2{p}^{3}{\phantom{\rule{0.16em}{0ex}}}^{3}D$, ${}^{3}S$, and ${}^{3}P$ shape resonances.

  • electron atom resonances the complex scaled multiconfigurational Spin Tensor electron propagator method for the 2 p be shape resonance problem
    Physical Review A, 2015
    Co-Authors: Tsogbayar Tsednee, Liyuan Liang, Danny L Yeager
    Abstract:

    We propose and develop the complex-scaled multiconfigurational Spin-Tensor electron propagator (CMCSTEP) technique for theoretical determination of resonance parameters with electron-atom and electron-molecule systems including open-shell and highly correlated atoms and molecules. The multiconfigurational Spin-Tensor electron propagator (MCSTEP) method developed and implemented by Yeager and co-workers in real space gives very accurate and reliable ionization potentials and attachment energies. The CMCSTEP method uses a complex-scaled multiconfigurational self-consistent field (CMCSCF) state as an initial state along with a dilated Hamiltonian where all of the electronic coordinates are scaled by a complex factor. The CMCSCF was developed and applied successfully to resonance problems earlier. We apply the CMCSTEP method to get ${}^{2}P\phantom{\rule{0.16em}{0ex}}{\text{Be}}^{\ensuremath{-}}$ shape resonance parameters using $14s11p5d,\phantom{\rule{0.16em}{0ex}}14s14p2d$, and $14s14p5d$ basis sets with a $2s2p3d$ complete active space. The obtained values of the resonance parameters are compared to previous results. Here CMCSTEP has been developed and used for a resonance problem. It appears to be among the most accurate and reliable techniques. Vertical ionization potentials and attachment energies in real space are typically within $\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.28em}{0ex}}\text{eV}$ or better of excellent experimental results and full configuration-interaction calculations with a good basis set. We expect the same sort of agreement in complex space.

  • Equivalent orbitals for multiconfigurational Spin‐Tensor electron propagator method (MCSTEP): The vertical ionization potentials of B, NO, CF, and OF
    International Journal of Quantum Chemistry, 2008
    Co-Authors: Danny L Yeager
    Abstract:

    The multiconfigurational Spin Tensor electron propagator method (MCSTEP) was developed as an implementation of electron propagator/single particle Green's function methods for ionization potentials (IPs) and electron affinities (EAs). MCSTEP was specifically designed for open shell and highly correlated (nondynamically correlated) initial states. For computational efficiency the initial state used in MCSTEP is typically a small complete active space (CAS) multiconfigurational self-consistent field (MCSCF) state. If in a molecule there are some degenerate orbitals which are not fully or half occupied, usual MCSCF calculations will make these orbitals inequivalent, i.e., the occupied ones will be different from the nonoccupied ones, so that the degeneracy is broken. In this article, we use a state averaged MCSCF method to get equivalent orbitals for the initial state and import the integrals into the subsequent MCSTEP calculations. This gives, in general, more reliable MCSTEP vertical IPs. © 2008 Wiley Periodicals, Inc., 2008

  • Approximate MCSCF optimization for multiconfigurational Spin-Tensor electron propagator method (MCSTEP): The vertical ionization potentials of CO, HCN, HNC, H2CO, and O3
    International Journal of Quantum Chemistry, 2007
    Co-Authors: Danny L Yeager
    Abstract:

    The multiconfigurational Spin Tensor electron propagator method (MCSTEP) was developed as an implementation of electron propagator/single particle Green's function methods. MCSTEP was specifically designed for open shell and highly correlated (nondynamically correlated) initial states. The initial state used in MCSTEP is typically a small complete active space (CAS) with multiconfigurational self-consistent field (MCSCF) state. In some cases, because of our use of a small CAS in MCSTEP, the Lagrangian eigenvalues of the MCSCF reference state are in an undesired order (u). The desired order (d) can usually be obtained by excluding one or more orbital rotations in MCSCF optimization between the doubly occupied and partially occupied orbitals. We systematically examine several cases where the undesired order occurs for the low-lying vertical MCSTEP ionization potentials (IPs) of the molecules CO, HCN, HNC, H2CO, and O3 with our recently established CAS choices for MCSCF/MCSTEP. By excluding one or more orbital rotations between the partially and doubly occupied orbitals, an approximate MCSCF reference state with the same CAS choice is obtained for use in standard MCSTEP calculations that, in general, gives more reliable vertical MCSTEP IPs. © 2007 Wiley Periodicals, Inc. J Quantum Chem, 2008

Chuanwei Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Quantum spiral Spin-Tensor magnetism
    Physical Review B, 2020
    Co-Authors: Xiaofan Zhou, Xi-wang Luo, Gang Chen, Suotang Jia, Chuanwei Zhang
    Abstract:

    The characterization of quantum magnetism in a large Spin ($\ensuremath{\ge}1$) system naturally involves both Spin vectors and Spin Tensors. While certain types of Spin-vector (e.g., ferromagnetic, spiral) and Spin-Tensor (e.g., nematic in frustrated lattices) orders have been investigated separately, the coexistence and correlation between them have not been well explored. Here, we propose a quantum spiral Spin-Tensor order on a Spin-1 Heisenberg chain subject to a spiral Spin-Tensor Zeeman field, which can be experimentally realized using a Raman-dressed cold atom optical lattice. We develop a method to fully characterize quantum phases of such spiral Tensor magnetism with the coexistence of Spin-vector and Spin-Tensor orders as well as their correlations using eight geometric parameters. Our method provides a powerful tool for characterizing Spin-1 quantum magnetism and opens an avenue for exploring magnetic orders and Spin-Tensor electronics and atomtronics in large-Spin systems.

  • topological triply degenerate points induced by Spin Tensor momentum couplings
    Physical Review Letters, 2018
    Co-Authors: Junpeng Hou, Fan Zhang, Chuanwei Zhang
    Abstract:

    The recent discovery of triply degenerate points (TDPs) in topological materials has opened a new perspective toward the realization of novel quasiparticles without counterparts in quantum field theory. The emergence of such protected nodes is often attributed to Spin-vector-momentum couplings. We show that the interplay between Spin-Tensor- and Spin-vector-momentum couplings can induce three types of TDPs, classified by different monopole charges (C=±2, ±1, 0). A Zeeman field can lift them into Weyl points with distinct numbers and charges. Different TDPs of the same type are connected by intriguing Fermi arcs at surfaces, and transitions between different types are accompanied by level crossings along high-symmetry lines. We further propose an experimental scheme to realize such TDPs in cold-atom optical lattices. Our results provide a framework for studying Spin-Tensor-momentum coupling-induced TDPs and other exotic quasiparticles.

  • topological triply degenerate points induced by Spin Tensor momentum couplings
    Physical Review Letters, 2018
    Co-Authors: Junpeng Hou, Fan Zhang, Chuanwei Zhang
    Abstract:

    The recent discovery of triply degenerate points (TDPs) in topological materials has opened a new perspective toward the realization of novel quasiparticles without counterparts in quantum field theory. The emergence of such protected nodes is often attributed to Spin-vector-momentum couplings. We show that the interplay between Spin-Tensor- and Spin-vector-momentum couplings can induce three types of TDPs, classified by different monopole charges ($\mathcal{C}=\ifmmode\pm\else\textpm\fi{}2$, $\ifmmode\pm\else\textpm\fi{}1$, 0). A Zeeman field can lift them into Weyl points with distinct numbers and charges. Different TDPs of the same type are connected by intriguing Fermi arcs at surfaces, and transitions between different types are accompanied by level crossings along high-symmetry lines. We further propose an experimental scheme to realize such TDPs in cold-atom optical lattices. Our results provide a framework for studying Spin-Tensor-momentum coupling-induced TDPs and other exotic quasiparticles.

  • Spin Tensor momentum coupled bose einstein condensates
    Physical Review Letters, 2017
    Co-Authors: Xi-wang Luo, Kuei Sun, Chuanwei Zhang
    Abstract:

    The recent experimental realization of Spin-orbit coupling for ultracold atomic gases provides a powerful platform for exploring many interesting quantum phenomena. In these studies, Spin represents the Spin vector (Spin 1/2 or Spin 1) and orbit represents the linear momentum. Here we propose a scheme to realize a new type of Spin-Tensor-momentum coupling (STMC) in Spin-1 ultracold atomic gases. We study the ground state properties of interacting Bose-Einstein condensates with STMC and find interesting new types of stripe superfluid phases and multicritical points for phase transitions. Furthermore, STMC makes it possible to study quantum states with dynamical stripe orders that display density modulation with a long tunable period and high visibility, paving the way for the direct experimental observation of a new dynamical supersolidlike state. Our scheme for generating STMC can be generalized to other systems and may open the door for exploring novel quantum physics and device applications.

  • Interacting Spin-orbit-coupled Spin-1 Bose-Einstein condensates
    Physical Review A, 2016
    Co-Authors: Kuei Sun, Yongping Zhang, Chuanwei Zhang
    Abstract:

    The recent experimental realization of Spin-orbit (SO) coupling for Spin-1 ultracold atoms opens an interesting avenue for exploring SO-coupling-related physics in large-Spin systems, which is generally unattainable in electronic materials. In this paper, we study the effects of interactions between atoms on the ground states and collective excitations of SO-coupled Spin-1 Bose-Einstein condensates (BECs) in the presence of a Spin-Tensor potential. We find that ferromagnetic interaction between atoms can induce a stripe phase exhibiting in-phase or out-of-phase modulating patterns between Spin-Tensor and zero-Spin-component density waves. We characterize the phase transitions between different phases using the Spin-Tensor density as well as the collective dipole motion of the BEC. We show that there exists a double maxon-roton structure in the Bogoliubov-excitation spectrum, attributed to the three band minima of the SO-coupled Spin-1 BEC.

Joseph T. Golab - One of the best experts on this subject based on the ideXlab platform.

Yu-ning Huang - One of the best experts on this subject based on the ideXlab platform.

  • extended intrinsic mean Spin Tensor for turbulence modelling in non inertial frame of reference
    Applied Mathematics and Mechanics-english Edition, 2008
    Co-Authors: Yu-ning Huang
    Abstract:

    We investigate the role of extended intrinsic mean Spin Tensor introduced in this work for turbulence modelling in a non-inertial frame of reference. It is described by the Euclidean group of transformations and, in particular, its significance and importance in the approach of the algebraic Reynolds stress modelling, such as in a nonlinear K-ɛ model. To this end and for illustration of the effect of extended intrinsic Spin Tensor on turbulence modelling, we examine several recently developed nonlinear K-ɛ models and compare their performance in predicting the homogeneous turbulent shear flow in a rotating frame of reference with LES data. Our results and analysis indicate that, only if the deficiencies of these models and the like be well understood and properly corrected, may in the near future, more sophisticated nonlinear K-ɛ models be developed to better predict complex turbulent flows in a non-inertial frame of reference.

  • On applying the extended intrinsic mean Spin Tensor to modelling the turbulence in non-inertial frames of reference
    Science in China Series G: Physics Mechanics and Astronomy, 2008
    Co-Authors: Yu-ning Huang
    Abstract:

    Modelling the turbulent flows in non-inertial frames of reference has long been a challenging task. Recently we introduced the notion of the “extended intrinsic mean Spin Tensor” for turbulence modelling and pointed out that, when applying the Reynolds stress models developed in the inertial frame of reference to modelling the turbulence in a non-inertial frame of reference, the mean Spin Tensor should be replaced by the extended intrinsic mean Spin Tensor to correctly account for the rotation effects induced by the non-inertial frame of reference, to conform in physics with the Reynolds stress transport equation. To exemplify the approach, we conducted numerical simulations of the fully developed turbulent channel flow in a rotating frame of reference by employing four non-linear K-e models. Our numerical results based on this approach at a wide range of Reynolds and Rossby numbers evince that, among the models tested, the non-linear K-e model of Huang and Ma and the non-linear K-e model of Craft, Launder and Suga can better capture the rotation effects and the resulting influence on the structures of turbulence, and therefore are satisfactorily applied to dealing with the turbulent flows of practical interest in engineering. The general approach worked out in this paper is also applied to the second-moment closure and the large-eddy simulation of turbulence.

  • Reynolds stress model involving the mean Spin Tensor.
    Physical review. E Statistical nonlinear and soft matter physics, 2004
    Co-Authors: Yu-ning Huang
    Abstract:

    In this work, we develop a Reynolds stress model along the line of the approach presented by Commun. Nonlinear Sci. Numer. Simul. 9, 543 (2004)]], aiming to assess the role and contribution of the mean Spin Tensor in turbulence modeling. Here, the constitutive functional for the Reynolds stress depends on the mean Spin Tensor as well as the mean stretching Tensor and its Jaumann derivative, the turbulent kinetic energy K , and the turbulent dissipation rate epsilon , which is at the complexity level of p=1,m=1 , and n=0 of a rate-type constitutive equation for the Reynolds stress proposed in the aforementioned paper. The explicit form for the Reynolds stress is obtained with recourse to the representation theorem and the theory of invariants developed in modern rational continuum mechanics, and, as an approximation, a nonlinear cubic K-epsilon model is worked out in which the model coefficients are analytically identified based on the experimental results of Tavoularis and Corrsin [J. Fluid Mech. 104, 311 (1981)]]. In addition, numerical results based on this model, in the forms of employing the Jaumann derivative and the Oldroyd derivative, respectively, for homogeneous turbulent shear flow and fully developed turbulent flow over a backward-facing step, are presented in comparison with those obtained based on a few previously proposed linear and nonlinear K-epsilon models, showing reasonably good agreement with the experimental results and the DNS data concerned and a better performance than the previously developed quadratic models.

  • Reynolds stress model involving the mean Spin Tensor.
    Physical Review E, 2004
    Co-Authors: Yu-ning Huang
    Abstract:

    In this work, we develop a Reynolds stress model along the line of the approach presented by Huang [Commun. Nonlinear Sci. Numer. Simul. 9, 543 (2004)], aiming to assess the role and contribution of the mean Spin Tensor in turbulence modeling. Here, the constitutive functional for the Reynolds stress depends on the mean Spin Tensor as well as the mean stretching Tensor and its Jaumann derivative, the turbulent kinetic energy $K$, and the turbulent dissipation rate $\ensuremath{\epsilon}$, which is at the complexity level of $p=1,m=1$, and $n=0$ of a rate-type constitutive equation for the Reynolds stress proposed in the aforementioned paper. The explicit form for the Reynolds stress is obtained with recourse to the representation theorem and the theory of invariants developed in modern rational continuum mechanics, and, as an approximation, a nonlinear cubic $K\text{\ensuremath{-}}\ensuremath{\epsilon}$ model is worked out in which the model coefficients are analytically identified based on the experimental results of Tavoularis and Corrsin [J. Fluid Mech. 104, 311 (1981)]. In addition, numerical results based on this model, in the forms of employing the Jaumann derivative and the Oldroyd derivative, respectively, for homogeneous turbulent shear flow and fully developed turbulent flow over a backward-facing step, are presented in comparison with those obtained based on a few previously proposed linear and nonlinear $K\text{\ensuremath{-}}\ensuremath{\epsilon}$ models, showing reasonably good agreement with the experimental results and the DNS data concerned and a better performance than the previously developed quadratic models.

Jeffrey A. Nichols - One of the best experts on this subject based on the ideXlab platform.

  • Complete basis set limit ionization potentials of O3 and NO2 using the multiconfigurational Spin Tensor electron propagator method (MCSTEP)
    Chemical Physics, 1998
    Co-Authors: Alexander J. Mckellar, Danny L Yeager, Dodi Heryadi, Jeffrey A. Nichols
    Abstract:

    We have calculated low-lying principal vertical ionization potentials (IPs) of O3 and NO2 with the multiconfigurational Spin Tensor electron propagator method (MCSTEP) using several different basis sets. We obtain an estimate of complete basis set limit (CBS) MCSTEP IPs. This is the first time CBS estimates have been used with MCSTEP. We show that MCSTEP is accurate and reliable compared with experiment at the CBS limit for obtaining low-lying vertical IPs for open shell molecules such as NO2 and highly correlated molecules such as O3. Our results confirm previous assignments of photoelectron peaks based on calculations made using less accurate methods.

  • Low‐lying ionization potentials of O3 and NO2 using the multiconfigurational Spin Tensor electron propagator method
    The Journal of Chemical Physics, 1996
    Co-Authors: Alexander J. Mckellar, Danny L Yeager, Jeffrey A. Nichols, Joseph T. Golab
    Abstract:

    The multiconfigurational Spin Tensor electron propagator method (MCSTEP) is a single particle Green’s function (or electron propagator) method for determining the low‐lying principal vertical ionization potentials (IPs) and electron affinities (EAs) of atoms and molecules. It was specifically designed to handle cases where the initial state has nondynamical correlation and/or is open shell. We have applied MCSTEP for the first time to triatomic molecules composed entirely of second row atoms. The two cases we present are O3 and NO2—for the former nondynamical correlation is present in the ground (initial) state and for the latter the ground (initial) state is open shell. MCSTEP results are accurate compared to experiment and other forefront theoretical techniques.

  • Multiconfigurational Spin Tensor electron propagator vertical ionization potentials for O2: Comparison to some other forefront methods using the same basis sets and geometries
    The Journal of Chemical Physics, 1995
    Co-Authors: Dodi Heryadi, Danny L Yeager, Joseph T. Golab, Jeffrey A. Nichols
    Abstract:

    In a recent paper in The Journal of Chemical Physics, we showed the potential energy curves for several cation states of O2 obtained using the multiconfigurational Spin Tensor electron propagator method (MCSTEP) with a 〈5s4p3d〉 basis set. In this communication we present vertical ionization potential calculations to the same O2 states. However, for the results reported here, exactly the same basis sets and geometries are used that were used for two other forefront methods; the coupled‐cluster reference electron propagator theory (CC‐EPT) and the Fock space multireference coupled‐cluster method (FSMRCC). Hence, more direct comparisons and contrasts among these methods are now available.

  • The multiconfigurational Spin Tensor electron propagator method (MCSTEP): Comparison with extended Koopmans' theorem results
    Theoretica chimica acta, 1995
    Co-Authors: Dodi Heryadi, Danny L Yeager, Joseph T. Golab, Jeffrey A. Nichols
    Abstract:

    We applied the multiconfigurational Spin Tensor electron propagator method (MCSTEP) for determining the lowest few (in energy) vertical ionization potentials (IPs) of HF, H_2O, NH_3, CH_4, N_2, CO, HNC, HCN, C_2H_2, H_2CO, and B_2H_6. We chose these molecules so that we could compare MCSTEP IPs with recently reported extended Koopmans' theorem (EKT) IPs on the same molecules. Using standard Dunning core-valence basis sets with relatively small complete active spaces, MCSTEP results are in very good to excellent agreement with experiment. These MCSTEP IPs are obtained using matrices no larger than 400 × 400. EKT matrices are even smaller; however, to obtain similar but generally slightly worse agreement with experiment, fairly large active spaces are required with EKT.

  • ionization potentials of ch2 a comparison of the multiconfigurational Spin Tensor electron propagator method with benchmark full configuration interaction and large scale multireference configuration interaction calculations
    Journal of Chemical Physics, 1994
    Co-Authors: Jeffrey A. Nichols, Danny L Yeager, Dodi Heryadi, Joseph T. Golab
    Abstract:

    Using the same basis sets and geometries as were previously used in ‘‘benchmark’’ full configuration interaction (FCI) calculations we compare the multiconfigurational Spin Tensor electron propagator method (MCSTEP) with FCI for the vertical ionization potentials (IPs) in CH2 below 19.0 eV. Our results show that MCSTEP using a full valence complete active space MCSCF initial state accurately obtains the lowest several principal vertical ionization potentials. We also determine vertical and adiabatic IPs in CH2 with MCSTEP using larger bases and compare to accurate large scale multireference singles and doubles CI with quadruple excitations estimated via a Davidson correction.