Study Of Ground State Properties Research Articles

Theoretical study of ground state properties of odd-A Cu isotopes in an analytical approach

Copper isotopes have been studied within various theoretical approaches, including the Shell model. Here, we describe their static properties using a new analytical approach. In the proposed model, we consider odd-A Cu isotopes as closed-shell nuclei plus one proton outside the [Formula: see text] shell gap. We calculate their static properties such as ground state energies, electric quadrupole moments and charge radii. The obtained results show good agreement with the experimental data, thus suggesting that our approach can be applicable to similar isotopic chains.

Study of Ground State Properties in Atomic Nuclei using Hartree Fock Bogoliubov Approach

Study of Ground State Properties in Atomic Nuclei using Hartree Fock Bogoliubov Approach

Study of ground state properties of carbon isotopes with deformed relativistic Hartree-Bogoliubov theory in continuum

Ground state properties of carbon isotopes, including root-mean-square radii, neutron separation energies, single particle spectra, and shapes are systematically studied with the deformed relativistic Hartree-Bogoliubov theory in continuum. The calculations with the effective interaction PK1 reproduce the available data reasonably well. The shell evolution in this isotopic chain is investigated by examining the single particle spectra. The inversion of neutron orbitals ν2s1/2 and ν1d5/2 compared with the order of neutron orbitals in stable nuclei is revealed in C15−20,22 when these nuclei are constrained to spherical shape. Neutron halos in 15,19,22C are studied in detail and their halo structures are mainly caused by the inversion of (ν2s1/2,ν1d5/2) and deformation effects. In particular, 15C and 22C are deformed halo nuclei with shape decoupling effects in ground states.

Electronic structure, mechanical, thermoelectric, optical, and thermodynamic properties of yttrium‐based quaternary Heusler alloys

We give a detailed study of ground state properties, magnetism, mechanical, thermoelectric, thermodynamic, and optical properties of rare-earth–based quaternary Heusler YFeMnAl and YFeMnGa alloys using the DFT and post-DFT methods. The structure optimizations, display the LiMgPdSn-type structure as stable phase with F-43 m symmetry. The spin-polarized band structure shows the alloys as perfect half-metallics with indirect band gap of 0.364 eV in YFeMnAl and 0.391 eV in YFeMnGa. The magnetism also supports their half-metallic character with an integral value of 3.00 μB estimated using the Slater-Pauling curve rule. Mechanical stability is calculated using the elastic constants which define their ductile nature. Transport coefficients are investigated to see their capability as green energy sources where thermopower “S” measurements at room temperature are −29 μVK−1 for YFeMnAl and −9 μVK−1 for YFeMnGa, with negative sign displaying their n-type majority heat carriers. Conversion efficiency of these materials descripts the figure of merit as 0.22 for YFeMnAl and 0.86 for YFeMnGa, respectively. The thermodynamic parameters like the heat capacity, Debye temperature, Grüneisen parameter, thermal expansion coefficient, and volume against pressure and temperature are sued to infer their stability at extreme conditions.

Structural and response properties of all BaTiO3 phases from density functional theory using the projector-augmented-wave methods

A study of ground state properties of bulk BaTiO3 perovskite crystal was conducted using first-principles density functional theory with local-density approximation (LDA) and generalized-gradient approximation (GGA), using the projector-augmented wave methods. Two different PAW potentials developed by Jollet–Torrent–Holzwarth (JTH) and Garrity–Bennett–Rabe–Vanderbilt (GBRV) are employed in the calculations. This study emphasize on electronic, structural and response properties of all BaTiO3 phases using different exchange correlation (XC) functionals and PAW potentials. Lattice parameters, cohesion energy, bulk modulus, Born effective charge, spontaneous polarization and charge densities of all BaTiO3 phases are calculated. In addition, gamma point phonon frequencies are computed with LDA. Structural and vibrational properties predicted using the two PAW potentials are consistent with experimental and previous theoretical studies for all BaTiO3 phases. It is observed that calculations with GGA yields structural properties much closer to reported experimental values than LDA. Spontaneous polarization computed using Berry phase approach for the three structures in ferroelectric phase are consistent with other theoretical results, but differ considerably from experimental values. The deviation of lattice parameters computed using different XC functionals directly affects the computed spontaneous polarization. An analysis of phonon mode symmetries and frequencies conformed to experimental findings in the literature.

Modeling nuclear weak-interaction processes with relativistic energy density functionals

Relativistic energy density functionals have become a standard framework for nuclear structure studies of ground state properties and collective excitations over the entire nuclide chart. In this paper, we review recent developments in modeling nuclear weak-interaction processes: Charge-exchange excitations and the role of isoscalar proton–neutron pairing, charged-current neutrino–nucleus reactions relevant for supernova evolution and neutrino detectors and calculation of β-decay rates for r-process nucleosynthesis.

On the interaction between gold and silver metal atoms and DNA/RNA nucleobases – a comprehensive computational study of ground state properties

Abstract The interaction between metal atoms and nucleobases has been a topic of high interest due to the wide scientific and technological implications. Combining density functional theory simulations with a literature overview, we achieved an exhaustive study of the ground state electronic properties of DNA/RNA nucleobases interacting with gold and silver atoms at three charge states: neutral, cationic, and anionic. We describe the nature of the stability and electronic properties in each hybrid metallic structure. In addition to the metal interacting with the five isolated nucleobases, we included their respective DNA-WC base pairs and one case with the protonated sugar-phosphate backbone. As a general trend, we discerned that the energetic ordering of isomers follows simple electrostatic rules as expected from previous studies. Also, we found that although the metal localizes almost all of the extra charge in the anionic system, a donation of charge is shared almost equally in the cationic system. Furthermore, the frontier orbitals of the cationic system tend to have more effects from the pairing and inclusion of the backbone than the anionic system. Finally, the electronic gap varies greatly among all of the considered structures and could be further used as a fingerprint when searching DNA-metal hybrid structures.

Non-classical correlations in a class of spin chains with long-range interactions and exactly solvable ground states

We introduce a class of spin models with long-range interactions—in the sense that they extend significantly beyond their nearest neighbors—whose ground states can be constructed analytically and that have a simple matrix product state representation. This enables the detailed study of ground state properties, such as correlation functions and entanglement, in the thermodynamic limit. The spin models presented here are closely related to lattice gases of strongly interacting polar molecules, or Rydberg atoms that feature an excluded volume or blockade interaction. While entanglement is only present between spins that are separated by no more than a blockade length, we show that non-classical correlations can extend much further, and we analyze them through quantum discord. We furthermore identify a set of seemingly critical points where the ground state approaches a crystalline state with a filling fraction that is given by the inverse of the blockade length. We analyze the scaling properties in the vicinity of this parameter region and show that the correlation length possesses a non-trivial dependence on the blockade length.

Materials properties of magnesium and calcium hydroxides from first-principles calculations

Recent experiments have revealed a good potential of applicability of multifunctional hydroxides X(OH)2 (X=Mg and Ca) in optoelectronic devices and emphasized the lack of fundamental understanding of their materials properties. This work presents systematic study of ground state properties, electronic structure, dielectric and optical properties of the materials by first-principles calculations within PBE-GGA and range-separated hybrid functional schemes as well as by using GW approximation. The relevant HSE06 hybrid functional mixing parameters were determined from a self-consistent adjustment to the electronic dielectric constant ∊∞. We show that the overall performance of our adaptation of the HSE06 functional via implementation of the modified amount of the Fock exchange is nearly best for the ground state properties as compared to the other relevant methods of Hartree–Fock and density-functional theory. Structural stability of the crystalline X(OH)2 hydroxides has been considered in static and dynamic aspects. The most important factors describing the bonding situation have been investigated, and a crystal-chemical integrity of the hydroxides has been analyzed. From electronic structure studies it was found that both materials are direct band gap insulators. Predictions for the fundamental band gaps were shown to be in the range of 7.7–8.3eV for Mg(OH)2 and 7.3–7.6eV for Ca(OH)2. The origin of the conduction and valence band states near the band edges has been studied in terms of orbital and site projected density of states as well as by comparison with the X-ray photoelectron spectroscopy measurements. It was shown that effective masses of carriers at the Γ-point in vicinity of the band extreme are strongly anisotropic and for the electrons are similar to those in the ZnO crystal. Optical properties of the bulk X(OH)2 hydroxides have been investigated in terms of the real and imaginary parts of the optical dielectric function calculated in GW approximation. Electronic character of anisotropy of optical properties has been clarified.

Polytypism of GaAs, InP, InAs, and InSb: Anab initiostudy

A systematic study of ground state properties of cubic (3$C$) and hexagonal (6$H$, 4$H$, 2$H$) polytypes of normal (nonnitride) III-V compounds is reported using well-converged density-functional calculations within local density approximation, ab initio pseudopotentials, and projector-augmented wave method. Equilibrium results are obtained for lattice parameters, cohesive energies, and bulk moduli. Internal degrees of freedom, i.e., atomic relaxations, are taken into account. Trends with the hexagonality are discussed. Within the axial next-nearest-neighbor Ising (ANNNI) model driving forces of the polytypism as well as the stacking fault formation are derived. The results are compared with available experimental data.

First-principles study of ground state properties of ZrH2

Structural, mechanical, electronic, and thermodynamic properties of fluorite and tetragonal phases of ZrH2 are systematically studied by employing the density functional theory within generalized gradient approximation. The existence of the bistable structure for ZrH2 is mainly due to the tetragonal distortions. And our calculated lattice constants for the stable face-centered tetragonal (fct) phase with c/a=0.885 are consistent well with experiments. Through calculating elastic constants, the mechanically unstable characters of face-centered cubic (fcc) phase and fct structure with c/a=1.111 are predicted. As for fct0.885 structure, our calculated elastic constants explicitly indicate that it is mechanically stable. Elastic moduli, Poisson’s ratio, and Debye temperature are derived from elastic constants. After analyzing total and partial densities of states and valence electron charge distribution, we conclude that the Zr–H bonds in ZrH2 exhibit weak covalent feature. But the ionic property is evident with about 1.5 electrons transferring from each Zr atom to H. Phonon spectrum results indicate that fct0.885 structure is dynamically stable, while the fcc and fct1.111 structures are unstable in accord with the mechanical stability analysis.

First principles calculation of finite temperature magnetism in Fe and Fe3C

Density functional calculations have proven to be a useful tool in the study of ground state properties of many materials. The investigation of finite temperature magnetism, on the other hand, has to rely usually on the usage of empirical models that allow the large number of evaluations of the systems Hamiltonian that are required to obtain the phase space sampling needed to obtain the free energy, specific heat, magnetization, susceptibility, and other quantities as function of temperature. We have demonstrated a solution to this problem that harnesses the computational power of today’s large massively parallel computers by combining a classical Wang–Landau Monte-Carlo calculation [F. Wang and D. P. Landau, Phys. Rev. Lett. 86, 2050 (2001)] with our first principles multiple scattering electronic structure code [Y. Wang et al., Phys. Rev. Lett. 75, 2867 (1995)] that allows the energy calculation of constrained magnetic states [M. Eisenbach et al., Proceedings of the Conference on High Performance Computing, Networking, Storage and Analysis (ACM, New York, 2009)]. We present our calculations of finite temperature properties of Fe and Fe3C using this approach and we find the Curie temperatures to be 980 and 425K, respectively.

Three-spin interactions in optical lattices and criticality in cluster Hamiltonians.

We demonstrate that in a triangular configuration of an optical lattice of two atomic species a variety of novel spin-1/2 Hamiltonians can be generated. They include effective three-spin interactions resulting from the possibility of atoms tunneling along two different paths. This motivates the study of ground state properties of various three-spin Hamiltonians in terms of their two-point and n-point correlations as well as the localizable entanglement. We present a Hamiltonian with a finite energy gap above its unique ground state for which the localizable entanglement length diverges for a wide interval of applied external fields, while at the same time the classical correlation length remains finite.

Polynomial combinatorial optimization methods for analysing the ground states of disordered systems

We discuss the application of polynomial combinatorial optimization algorithms to extract the universal zero-temperature properties of various disordered systems. Dijkstras algorithm is used for models of non-directed elastic lines on general regular graphs with isotropically correlated random potentials. The successive shortest path algorithm for minimum-costflow problems is applied for the study of ground state properties and the entanglement of many elastic lines in a disordered environment and the disorder-induced loop percolation transition in a vortex glass model. The preflow-push algorithm for minimum-cut–maximum-flow problems is used for the investigation of a roughening transition occurring in a model for elastic manifolds in a periodic potential in the presence of point disorder.

Plane wave pseudopotential study of ground state properties and electrochemical description of thallium nitride

We present a study of thallium nitride using the ab initio plane wave pseudopotential method in the local density approximation. The ground state properties of the hypothetical zinc-blende TlN have been reported as well as the electronic and chemical qualitative and quantitative descriptions. Results show that the main characteristics of TlN are similar to those of the other nitrides, but differ from a chemical bonding point of view and from the band-gap width which is almost negligible.

Adaptive optimization of wave functions for fermion lattice models

We present a simulation algorithm for Hamiltonian fermion lattice models. A guiding trial wave function is adaptively optimized during Monte Carlo evolution. We apply the method to the two dimensional Gross-Neveu model and analyze systematc errors in the study of ground state properties. We show that accurate measurements can be achieved by a proper extrapolation in the algorithm free parameters.

Ab initio theoretical investigation of the hydrogen-, lithium-, sodium- and potassium cation affinities of the XY (X,Y=H, Li, Na, K) alkali dimers

Ab initio variational calculations were performed for the study of ground state properties of the XYZ+ (X,Y,Z=H, Li, Na, K) homonuclear and heteronuclear cationic alkali trimer ions. Their molecular geometry was determined and all the discussed systems were predicted to be stable in the gas phase. The hydrogen-, lithium-, sodium- and potassium cation affinities, CA, of the XY (X,Y=H, Li, Na, K) alkali dimers were treated. According to the theoretical investigations—considering the mentioned cation affinities of the M=H2, LiH, Li2, NaH, NaLi, Na2, KH, LiK, NaK dimers—the relations in the series are:CA(M⋯H+)>CA(M⋯Li+)>CA(M⋯Na+)>CA(M⋯K+).

Variational theory of bulk4Hewith shadow wave functions: Ground state and the phonon-maxon-roton spectrum

We apply an efficient optimization scheme to shadow wave functions (SWF's) for the ground state of liquid and solid ${}^{4}\mathrm{He}$. Results improve on previous variational energies in both phases. In the liquid, the gain over a wave function with only pair and triplet correlations increases with density, providing a quantitative estimate of the increasing effect of higher-order correlations. The discrepancy with the exact ground-state energy is nearly constant over a wide range of densities, yielding excellent estimates for the equilibrium, freezing, and melting densities. The optimal SWF's can be represented with high precision by density-independent sets of variational parameters for the liquid and the solid phases. An extensive study of ground-state properties demonstrates the uniformly good quality of the variational description afforded by the optimized SWF's. Based on such an accurate representation of the ground state, and including the correct long-range correlations due to the zero-point motion of phonons, we compute the excitation spectrum and the strength of the single quasiparticle excitation peak. While the use of optimized SWF's confirms the accuracy of previous studies in the maxon-roton region, the proper treatment of long-range correlations allows us to extend to the phonon region the agreement between theory and experiment. We simulate relatively large systems in order to explore the long-wavelength regime in detail. Even down to wave vectors where the excitation energy exhibits a highly linear dispersion, which would suggest a harmonic phonon mode, the kinetic and potential energies of the excitation are far from verifying equipartition. This result is supported by additional diffusion Monte Carlo simulations within the fixed node approximation. We locate the onset of the harmonic regime for the long-wavelength excitations at an extremely small value of the wave vector, $k\ensuremath{\lesssim}0.05 {\mathrm{\AA{}}}^{\ensuremath{-}1}$.

A perfect Hashing function for exact diagonalization of many-body systems of identical particles

In exact diagonalization studies of ground state properties of an interacting system using Lánczos, it is crucial to find an efficient mapping from the configuration space to the index of the Lánczos vector. Here, we formulate a mapping (hashing function) that is simple to calculate for identical many-body systems of both fermions and bosons. A unique feature of our hashing functions is that they map many particle configurations to a sequence of consecutive integers. They are therefore optimal in using computer memory.

XPS satellite structure of nickel complex compounds as an analytical tool for studies of ground state properties

Reliability of iterative EHT method to reproduce (i) the energy and the atomic character of electronic molecular states of large nickel complex compounds, (ii) the energy separation between main Ni 2p photoeleotron line and satellites, and (iii) their relative intensities is studied comparing EHT data and SCF-DV-Xα results with experimental Ni Lα and S Kß X-ray emission bands and Ni 2p Apectra. The results of EHT calculations applying Larsson's charge-transfer concept suggest meaningful relationship between satellite parameters and electronegativity in NiX n± 6 ions contrary to a more complex correlation due to back bonding and charge delocalization in large chelate systems.