NASA Technical Reports Server (NTRS)
Arnold, J. O.; Nicholls, R. W.
1973-01-01
The CN ground state dissociation energy and the sum of squares of the electronic transition moments of the CN violet bands have been simultaneously determined from spectral emission measurements behind incident shock waves. The unshocked test gases were composed of various CO2-CO-N2-Ar mixtures, and the temperatures behind the incident shocks ranged from 3500 to 8000 K. The variation of the electronic transition moment with internuclear separation was found to be small for both the CN violet and red band systems.
Ground state energy of large polaron systems
Benguria, Rafael D.; Frank, Rupert L.; Lieb, Elliott H.
2015-02-15
The last unsolved problem about the many-polaron system, in the Pekar–Tomasevich approximation, is the case of bosons with the electron-electron Coulomb repulsion of strength exactly 1 (the “neutral case”). We prove that the ground state energy, for large N, goes exactly as −N{sup 7/5}, and we give upper and lower bounds on the asymptotic coefficient that agree to within a factor of 2{sup 2/5}.
The factorization method and ground state energy bounds
NASA Astrophysics Data System (ADS)
Schmutz, M.
1985-04-01
We discuss the relationship between the factorization method and the Barnsley bound to the ground state energy. The latter method is extended in such a way that both lower and upper analytic bounds can be obtained.
Mass coefficient and Grodzins relation for the ground-state band and {gamma} band
Jolos, R. V.; Brentano, P. von
2006-12-15
It is shown that the available experimental data on the energies of the first and the {gamma}-vibrational 2{sup +} states and the reduced E2 transition probabilities from these states to the ground state require for the explanation significantly different values of the mass coefficients for the rotational motion and {gamma}-vibrations.
Ground-State Band and Deformation of the Z = 102 Isotope N {sup 254}
Reiter, P.; Khoo, T.L.; Lister, C.J.; Seweryniak, D.; Ahmad, I.; Alcorta, M.; Carpenter, M.P.; Cizewski, J.A.; Davids, C.N.; Gervais, G.; Greene, J.P.; Henning, W.F.; Janssens, R.V.; Lauritsen, T.; Siem, S.; Sonzogni, A.A.; Sullivan, D.; Uusitalo, J.; Wiedenhoever, I.; Amzal, N.; Butler, P.A.; Chewter, A.J.; Greenlees, P.T.; Herzberg, R.; Jones, G.D.; Cizewski, J.A.; Ding, K.Y.; Fotiades, N.; Fox, J.D.; Korten, W.; Vetter, K.; Siem, S.
1999-01-01
The ground-state band of the Z=102 isotope {sup 254}No has been identified up to spin 14, indicating that the nucleus is deformed. The deduced quadrupole deformation, {beta}=0.27 , is in agreement with theoretical predictions. These observations confirm that the shell-correction energy responsible for the stability of transfermium nuclei is partly derived from deformation. The survival of {sup 254}No up to spin 14 means that its fission barrier persists at least up to that spin. {copyright} {ital 1999} {ital The American Physical Society }
Estimation of beryllium ground state energy by Monte Carlo simulation
Kabir, K. M. Ariful; Halder, Amal
2015-05-15
Quantum Monte Carlo method represent a powerful and broadly applicable computational tool for finding very accurate solution of the stationary Schrödinger equation for atoms, molecules, solids and a variety of model systems. Using variational Monte Carlo method we have calculated the ground state energy of the Beryllium atom. Our calculation are based on using a modified four parameters trial wave function which leads to good result comparing with the few parameters trial wave functions presented before. Based on random Numbers we can generate a large sample of electron locations to estimate the ground state energy of Beryllium. Our calculation gives good estimation for the ground state energy of the Beryllium atom comparing with the corresponding exact data.
A Remark on the Ground State Energy of Bosonic Atoms
NASA Astrophysics Data System (ADS)
Hogreve, H.
2011-08-01
Monotonicity properties of the ground state energy of bosonic atoms as established in a recent paper by M.K.H. Kiessling [J. Stat. Phys. 139:1063 (2009)] are studied. Symmetry and scaling arguments lead to a more direct proof of a slightly stronger result of this monotonicity and the behavior of the ground state energy as a function of the number of bosonic electrons. Furthermore, invoking appropriate lower and upper bounds on two-electron systems, the stability of the bosonics He- ion is rigorously demonstrated.
The Ground State Energy of Heavy Atoms: The Leading Correction
NASA Astrophysics Data System (ADS)
Handrek, Michael; Siedentop, Heinz
2015-10-01
For heavy atoms (large atomic number Z) described by no-pair operators in the Furry picture, we find the ground state's leading energy correction. We compare the result with (semi-)empirical values and Schwinger's prediction showing more than qualitative agreement.
Ground-state energy and relativistic corrections for positronium hydride
Bubin, Sergiy; Varga, Kalman
2011-07-15
Variational calculations of the ground state of positronium hydride (HPs) are reported, including various expectation values, electron-positron annihilation rates, and leading relativistic corrections to the total and dissociation energies. The calculations have been performed using a basis set of 4000 thoroughly optimized explicitly correlated Gaussian basis functions. The relative accuracy of the variational energy upper bound is estimated to be of the order of 2x10{sup -10}, which is a significant improvement over previous nonrelativistic results.
Improvement in a phenomenological formula for ground state binding energies
NASA Astrophysics Data System (ADS)
Gangopadhyay, G.
2016-07-01
The phenomenological formula for ground state binding energy derived earlier [G. Gangopadhyay, Int. J. Mod. Phys. E 20 (2011) 179] has been modified. The parameters have been obtained by fitting the latest available tabulation of experimental values. The major modifications include a new term for pairing and introduction of a new neutron magic number at N = 160. The new formula reduced the root mean square deviation to 363keV, a substantial improvement over the previous version of the formula.
Ground-state and pairing-vibrational bands with equal quadrupole collectivity in 124Xe
Radich, A. J.; Garrett, P. E.; Allmond, J. M.; Andreoiu, C.; Ball, G. C.; Bianco, L.; Bildstein, V.; Chagnon-Lessard, S.; Cross, D. S.; Demand, G. A.; et al
2015-04-01
The nuclear structure of 124Xe has been investigated via measurements of the β+/EC decay of 124Cs with the 8π γ-ray spectrometer at the TRIUMF-ISAC facility. The data collected have enabled branching ratio measurements of weak, low-energy transitions from highly excited states, and the 2+ → 0+ in-band transitions have been observed. Combining these results with those from a previous Coulomb excitation study, $B(E2; 2^+_3 → 0^+_2)$ = 78(13) W.u. and $B(E2; 2^+_4 → 0^+_3)$ = 53(12) W.u. were determined. The $0^+_3$ state, in particular, is interpreted as the main fragment of the proton-pairing vibrational band identified in a previous 122Te(3He,n)124Xemore » measurement, and has quadrupole collectivity equal to, within uncertainty, that of the ground-state band.« less
Variable energy, high flux, ground-state atomic oxygen source
NASA Technical Reports Server (NTRS)
Chutjian, Ara (Inventor); Orient, Otto J. (Inventor)
1987-01-01
A variable energy, high flux atomic oxygen source is described which is comprised of a means for producing a high density beam of molecules which will emit O(-) ions when bombarded with electrons; a means of producing a high current stream of electrons at a low energy level passing through the high density beam of molecules to produce a combined stream of electrons and O(-) ions; means for accelerating the combined stream to a desired energy level; means for producing an intense magnetic field to confine the electrons and O(-) ions; means for directing a multiple pass laser beam through the combined stream to strip off the excess electrons from a plurality of the O(-) ions to produce ground-state O atoms within the combined stream; electrostatic deflection means for deflecting the path of the O(-) ions and the electrons in the combined stream; and, means for stopping the O(-) ions and the electrons and for allowing only the ground-state O atoms to continue as the source of the atoms of interest. The method and apparatus are also adaptable for producing other ground-state atoms and/or molecules.
Unparticle contribution to the hydrogen atom ground state energy
NASA Astrophysics Data System (ADS)
Wondrak, Michael F.; Nicolini, Piero; Bleicher, Marcus
2016-08-01
In the present work we study the effect of unparticle modified static potentials on the energy levels of the hydrogen atom. By using Rayleigh-Schrödinger perturbation theory, we obtain the energy shift of the ground state and compare it with experimental data. Bounds on the unparticle energy scale ΛU as a function of the scaling dimension dU and the coupling constant λ are derived. We show that there exists a parameter region where bounds on ΛU are stringent, signaling that unparticles could be tested in atomic physics experiments.
Ground state energies from converging and diverging power series expansions
NASA Astrophysics Data System (ADS)
Lisowski, C.; Norris, S.; Pelphrey, R.; Stefanovich, E.; Su, Q.; Grobe, R.
2016-10-01
It is often assumed that bound states of quantum mechanical systems are intrinsically non-perturbative in nature and therefore any power series expansion methods should be inapplicable to predict the energies for attractive potentials. However, if the spatial domain of the Schrödinger Hamiltonian for attractive one-dimensional potentials is confined to a finite length L, the usual Rayleigh-Schrödinger perturbation theory can converge rapidly and is perfectly accurate in the weak-binding region where the ground state's spatial extension is comparable to L. Once the binding strength is so strong that the ground state's extension is less than L, the power expansion becomes divergent, consistent with the expectation that bound states are non-perturbative. However, we propose a new truncated Borel-like summation technique that can recover the bound state energy from the diverging sum. We also show that perturbation theory becomes divergent in the vicinity of an avoided-level crossing. Here the same numerical summation technique can be applied to reproduce the energies from the diverging perturbative sums.
a New Phenomenological Formula for Ground-State Binding Energies
NASA Astrophysics Data System (ADS)
Gangopadhyay, G.
A phenomenological formula based on liquid drop model has been proposed for ground-state binding energies of nuclei. The effect due to bunching of single particle levels has been incorporated through a term resembling the one-body Hamiltonian. The effect of n-p interaction has been included through a function of valence nucleons. A total of 50 parameters has been used in the present calculation. The root mean square (r.m.s.) deviation for the binding energy values for 2140 nuclei comes out to be 0.376 MeV, and that for 1091 alpha decay energies is 0.284 MeV. The correspondence with the conventional liquid drop model is discussed.
Centrifugal stretching along the ground state band of {sup 168}Hf
Costin, A.; Pietralla, N.; Reese, M.; Moeller, O.; Ai, H.; Casten, R. F.; Heinz, A.; McCutchan, E. A.; Meyer, D. A.; Qian, J.; Werner, V.; Dusling, K.; Fitzpatrick, C. R.; Guerdal, G.; Petkov, P.; Rainovski, G.
2009-02-15
The lifetimes of the J{sup {pi}}=4{sup +}, 6{sup +}, 8{sup +}, and 10{sup +} levels along the ground state band in {sup 168}Hf were measured by means of the recoil distance Doppler shift (RDDS) method using the New Yale Plunger Device (NYPD) and the SPEEDY detection array at Wright Nuclear Structure Laboratory of Yale University. Excited states in {sup 168}Hf were populated using the {sup 124}Sn({sup 48}Ti,4n) fusion evaporation reaction. The new lifetime values are sufficiently precise to clearly prove the increase of quadrupole deformation as a function of angular momentum in the deformed nucleus {sup 168}Hf. The data agree with the predictions from the geometrical confined {beta}-soft (CBS) rotor model that involves centrifugal stretching in a soft potential.
Ground state energy from the single trajectory propagation of the Schrödinger-Langevin equation
NASA Astrophysics Data System (ADS)
Chou, Chia-Chun
2015-07-01
The Schrödinger-Langevin equation is approximately solved for the ground state energy of quantum systems by propagating one single trajectory at a fixed point. Equations of motion for the amplitude of the wave function and the spatial derivatives of the complex action are derived through use of the derivative propagation method. The ground state energy is calculated from the amplitude of the wave function propagated along the single trajectory. Excellent ground state energies are obtained for the Morse potential, the strongly anharmonic potential, the coupled Morse oscillator-harmonic oscillator system, and the ground vibrational state of methyl iodide.
Ground-state and pairing-vibrational bands with equal quadrupole collectivity in ^{124}Xe
Radich, A. J.; Garrett, P. E.; Allmond, J. M.; Andreoiu, C.; Ball, G. C.; Bianco, L.; Bildstein, V.; Chagnon-Lessard, S.; Cross, D. S.; Demand, G. A.; Diaz Varela, A.; Dunlop, R.; Finlay, P.; Garnsworthy, A. B.; Hackman, G.; Hadinia, B.; Jigmeddorj, B.; Laffoley, A. T.; Leach, K. G.; Michetti-Wilson, J.; Orce, J. N.; Rajabali, M. M.; Rand, E. T.; Starosta, K.; Sumithrarachchi, C. S.; Svensson, C. E.; Triambak, S.; Wang, Z. M.; Wood, J. L.; Wong, J.; Williams, S. J.; Yates, S. W.
2015-04-01
The nuclear structure of ^{124}Xe has been investigated via measurements of the β^{+}/EC decay of ^{124}Cs with the 8π γ-ray spectrometer at the TRIUMF-ISAC facility. The data collected have enabled branching ratio measurements of weak, low-energy transitions from highly excited states, and the 2^{+} → 0^{+} in-band transitions have been observed. Combining these results with those from a previous Coulomb excitation study, $B(E2; 2^+_3 → 0^+_2)$ = 78(13) W.u. and $B(E2; 2^+_4 → 0^+_3)$ = 53(12) W.u. were determined. The $0^+_3$ state, in particular, is interpreted as the main fragment of the proton-pairing vibrational band identified in a previous ^{122}Te(^{3}He,n)^{124}Xe measurement, and has quadrupole collectivity equal to, within uncertainty, that of the ground-state band.
Ground-state energies of the nonlinear sigma model and the Heisenberg spin chains
NASA Technical Reports Server (NTRS)
Zhang, Shoucheng; Schulz, H. J.; Ziman, Timothy
1989-01-01
A theorem on the O(3) nonlinear sigma model with the topological theta term is proved, which states that the ground-state energy at theta = pi is always higher than the ground-state energy at theta = 0, for the same value of the coupling constant g. Provided that the nonlinear sigma model gives the correct description for the Heisenberg spin chains in the large-s limit, this theorem makes a definite prediction relating the ground-state energies of the half-integer and the integer spin chains. The ground-state energies obtained from the exact Bethe ansatz solution for the spin-1/2 chain and the numerical diagonalization on the spin-1, spin-3/2, and spin-2 chains support this prediction.
Lower bounds to energies for cusped-gaussian wavefunctions. [hydrogen atom ground state
NASA Technical Reports Server (NTRS)
Eaves, J. O.; Walsh, B. C.; Steiner, E.
1974-01-01
Calculations for the ground states of H, He, and Be, conducted by Steiner and Sykes (1972), show that the inclusion of a very small number of cusp functions can lead to a substantial enhancement of the quality of the Gaussian basis used in molecular wavefunction computations. The properties of the cusped-Gaussian basis are investigated by a calculation of lower bounds concerning the ground state energy of the hydrogen atom.
NASA Astrophysics Data System (ADS)
Delahaye, Thibault; Nikitin, Andrei; Rey, Michaël; Szalay, Péter G.; Tyuterev, Vladimir G.
2014-09-01
In this paper we report a new ground state potential energy surface for ethylene (ethene) C2H4 obtained from extended ab initio calculations. The coupled-cluster approach with the perturbative inclusion of the connected triple excitations CCSD(T) and correlation consistent polarized valence basis set cc-pVQZ was employed for computations of electronic ground state energies. The fit of the surface included 82 542 nuclear configurations using sixth order expansion in curvilinear symmetry-adapted coordinates involving 2236 parameters. A good convergence for variationally computed vibrational levels of the C2H4 molecule was obtained with a RMS(Obs.-Calc.) deviation of 2.7 cm-1 for fundamental bands centers and 5.9 cm-1 for vibrational bands up to 7800 cm-1. Large scale vibrational and rotational calculations for 12C2H4, 13C2H4, and 12C2D4 isotopologues were performed using this new surface. Energy levels for J = 20 up to 6000 cm-1 are in a good agreement with observations. This represents a considerable improvement with respect to available global predictions of vibrational levels of 13C2H4 and 12C2D4 and rovibrational levels of 12C2H4.
Surface modification using low energy ground state ion beams
NASA Technical Reports Server (NTRS)
Chutjian, Ara (Inventor); Hecht, Michael H. (Inventor); Orient, Otto J. (Inventor)
1990-01-01
A method of effecting modifications at the surfaces of materials using low energy ion beams of known quantum state, purity, flux, and energy is presented. The ion beam is obtained by bombarding ion-generating molecules with electrons which are also at low energy. The electrons used to bombard the ion generating molecules are separated from the ions thus obtained and the ion beam is directed at the material surface to be modified. Depending on the type of ion generating molecules used, different ions can be obtained for different types of surface modifications such as oxidation and diamond film formation. One area of application is in the manufacture of semiconductor devices from semiconductor wafers.
Learning Approach on the Ground State Energy Calculation of Helium Atom
Shah, Syed Naseem Hussain
2010-07-28
This research investigated the role of learning approach on the ground state energy calculation of Helium atom in improving the concepts of science teachers at university level. As the exact solution of several particles is not possible here we used approximation methods. Using this method one can understand easily the calculation of ground state energy of any given function. Variation Method is one of the most useful approximation methods in estimating the energy eigen values of the ground state and the first few excited states of a system, which we only have a qualitative idea about the wave function.The objective of this approach is to introduce and involve university teacher in new research, to improve their class room practices and to enable teachers to foster critical thinking in students.
Learning Approach on the Ground State Energy Calculation of Helium Atom
NASA Astrophysics Data System (ADS)
Shah, Syed Naseem Hussain
2010-07-01
This research investigated the role of learning approach on the ground state energy calculation of Helium atom in improving the concepts of science teachers at university level. As the exact solution of several particles is not possible here we used approximation methods. Using this method one can understand easily the calculation of ground state energy of any given function. Variation Method is one of the most useful approximation methods in estimating the energy eigen values of the ground state and the first few excited states of a system, which we only have a qualitative idea about the wave function. The objective of this approach is to introduce and involve university teacher in new research, to improve their class room practices and to enable teachers to foster critical thinking in students.
Tree based machine learning framework for predicting ground state energies of molecules
NASA Astrophysics Data System (ADS)
Himmetoglu, Burak
2016-10-01
We present an application of the boosted regression tree algorithm for predicting ground state energies of molecules made up of C, H, N, O, P, and S (CHNOPS). The PubChem chemical compound database has been incorporated to construct a dataset of 16 242 molecules, whose electronic ground state energies have been computed using density functional theory. This dataset is used to train the boosted regression tree algorithm, which allows a computationally efficient and accurate prediction of molecular ground state energies. Predictions from boosted regression trees are compared with neural network regression, a widely used method in the literature, and shown to be more accurate with significantly reduced computational cost. The performance of the regression model trained using the CHNOPS set is also tested on a set of distinct molecules that contain additional Cl and Si atoms. It is shown that the learning algorithms lead to a rich and diverse possibility of applications in molecular discovery and materials informatics.
The Network Source Location Problem: Ground State Energy, Entropy and Effects of Freezing
NASA Astrophysics Data System (ADS)
Huang, Haiping; Raymond, Jack; Wong, K. Y. Michael
2014-07-01
Ground state entropy of the network source location problem is evaluated at both the replica symmetric level and one-step replica symmetry breaking level using the entropic cavity method. The regime that is a focus of this study, is closely related to the vertex cover problem with randomly quenched covered nodes. The resulting entropic message passing inspired decimation and reinforcement algorithms are used to identify the optimal location of sources in single instances of transportation networks. The conventional belief propagation without taking the entropic effect into account is also compared. We find that in the glassy phase the entropic message passing inspired decimation yields a lower ground state energy compared to the belief propagation without taking the entropic effect. Using the extremal optimization algorithm, we study the ground state energy and the fraction of frozen hubs, and extend the algorithm to collect statistics of the entropy. The theoretical results are compared with the extremal optimization results.
The role of correlation in the ground state energy of confined helium atom
Aquino, N.
2014-01-14
We analyze the ground state energy of helium atom confined by spherical impenetrable walls, and the role of the correlation energy in the total energy. The confinement of an atom in a cavity is one way in which we can model the effect of the external pressure on an atom. The calculations of energy of the system are carried out by the variational method. We find that the correlation energy remains almost constant for a range values of size of the boxes analyzed.
On Asymptotic Stability in Energy Space of Ground States for Nonlinear Schrödinger Equations
NASA Astrophysics Data System (ADS)
Cuccagna, Scipio; Mizumachi, Tetsu
2008-11-01
We consider nonlinear Schrödinger equations iu_t +Δ u +β (|u|^2)u=0 , text{for} (t,x)in mathbb{R}× mathbb{R}^d, where d ≥ 3 and β is smooth. We prove that symmetric finite energy solutions close to orbitally stable ground states converge to a sum of a ground state and a dispersive wave as t → ∞ assuming the so called the Fermi Golden Rule (FGR) hypothesis. We improve the “sign condition” required in a recent paper by Gang Zhou and I.M.Sigal.
The beta-decay scheme of 232Fr and the K=0 ground-state band in 232Ra
Perajarvi, K.; Cerny, J.; Fraile, L.M.; Jokinen, A.; Kankainen, A.; Koster, U.; Aysto, J.; ISOLDE Collaboration
2004-04-16
The beta-decay of 232Fr to excited states in 232Ra has been studied using gamma-gamma coincidence detection combined with the isotope separator on-line technique at the ISOLDE PSB facility at CERN. Earlier findings are confirmed and three new gamma-lines are reported. In addition to the beta-decay characteristics of 232Fr, the K = 0 ground-state band in 232Ra is identified. A yield survey of neutron-rich Fr isotopes, important also for the EURISOL project, is incorporated.
Delahaye, Thibault Rey, Michaël Tyuterev, Vladimir G.; Nikitin, Andrei; Szalay, Péter G.
2014-09-14
In this paper we report a new ground state potential energy surface for ethylene (ethene) C{sub 2}H{sub 4} obtained from extended ab initio calculations. The coupled-cluster approach with the perturbative inclusion of the connected triple excitations CCSD(T) and correlation consistent polarized valence basis set cc-pVQZ was employed for computations of electronic ground state energies. The fit of the surface included 82 542 nuclear configurations using sixth order expansion in curvilinear symmetry-adapted coordinates involving 2236 parameters. A good convergence for variationally computed vibrational levels of the C{sub 2}H{sub 4} molecule was obtained with a RMS(Obs.–Calc.) deviation of 2.7 cm{sup −1} for fundamental bands centers and 5.9 cm{sup −1} for vibrational bands up to 7800 cm{sup −1}. Large scale vibrational and rotational calculations for {sup 12}C{sub 2}H{sub 4}, {sup 13}C{sub 2}H{sub 4}, and {sup 12}C{sub 2}D{sub 4} isotopologues were performed using this new surface. Energy levels for J = 20 up to 6000 cm{sup −1} are in a good agreement with observations. This represents a considerable improvement with respect to available global predictions of vibrational levels of {sup 13}C{sub 2}H{sub 4} and {sup 12}C{sub 2}D{sub 4} and rovibrational levels of {sup 12}C{sub 2}H{sub 4}.
NASA Astrophysics Data System (ADS)
Schreck, Simon; Pietzsch, Annette; Kennedy, Brian; Såthe, Conny; Miedema, Piter S.; Techert, Simone; Strocov, Vladimir N.; Schmitt, Thorsten; Hennies, Franz; Rubensson, Jan-Erik; Föhlisch, Alexander
2016-01-01
Thermally driven chemistry as well as materials’ functionality are determined by the potential energy surface of a systems electronic ground state. This makes the potential energy surface a central and powerful concept in physics, chemistry and materials science. However, direct experimental access to the potential energy surface locally around atomic centers and to its long-range structure are lacking. Here we demonstrate how sub-natural linewidth resonant inelastic soft x-ray scattering at vibrational resolution is utilized to determine ground state potential energy surfaces locally and detect long-range changes of the potentials that are driven by local modifications. We show how the general concept is applicable not only to small isolated molecules such as O2 but also to strongly interacting systems such as the hydrogen bond network in liquid water. The weak perturbation to the potential energy surface through hydrogen bonding is observed as a trend towards softening of the ground state potential around the coordinating atom. The instrumental developments in high resolution resonant inelastic soft x-ray scattering are currently accelerating and will enable broad application of the presented approach. With this multidimensional potential energy surfaces that characterize collective phenomena such as (bio)molecular function or high-temperature superconductivity will become accessible in near future.
Schreck, Simon; Pietzsch, Annette; Kennedy, Brian; Såthe, Conny; Miedema, Piter S.; Techert, Simone; Strocov, Vladimir N.; Schmitt, Thorsten; Hennies, Franz; Rubensson, Jan-Erik; Föhlisch, Alexander
2016-01-01
Thermally driven chemistry as well as materials’ functionality are determined by the potential energy surface of a systems electronic ground state. This makes the potential energy surface a central and powerful concept in physics, chemistry and materials science. However, direct experimental access to the potential energy surface locally around atomic centers and to its long-range structure are lacking. Here we demonstrate how sub-natural linewidth resonant inelastic soft x-ray scattering at vibrational resolution is utilized to determine ground state potential energy surfaces locally and detect long-range changes of the potentials that are driven by local modifications. We show how the general concept is applicable not only to small isolated molecules such as O2 but also to strongly interacting systems such as the hydrogen bond network in liquid water. The weak perturbation to the potential energy surface through hydrogen bonding is observed as a trend towards softening of the ground state potential around the coordinating atom. The instrumental developments in high resolution resonant inelastic soft x-ray scattering are currently accelerating and will enable broad application of the presented approach. With this multidimensional potential energy surfaces that characterize collective phenomena such as (bio)molecular function or high-temperature superconductivity will become accessible in near future. PMID:26821751
Schreck, Simon; Pietzsch, Annette; Kennedy, Brian; Såthe, Conny; Miedema, Piter S; Techert, Simone; Strocov, Vladimir N; Schmitt, Thorsten; Hennies, Franz; Rubensson, Jan-Erik; Föhlisch, Alexander
2016-01-01
Thermally driven chemistry as well as materials' functionality are determined by the potential energy surface of a systems electronic ground state. This makes the potential energy surface a central and powerful concept in physics, chemistry and materials science. However, direct experimental access to the potential energy surface locally around atomic centers and to its long-range structure are lacking. Here we demonstrate how sub-natural linewidth resonant inelastic soft x-ray scattering at vibrational resolution is utilized to determine ground state potential energy surfaces locally and detect long-range changes of the potentials that are driven by local modifications. We show how the general concept is applicable not only to small isolated molecules such as O2 but also to strongly interacting systems such as the hydrogen bond network in liquid water. The weak perturbation to the potential energy surface through hydrogen bonding is observed as a trend towards softening of the ground state potential around the coordinating atom. The instrumental developments in high resolution resonant inelastic soft x-ray scattering are currently accelerating and will enable broad application of the presented approach. With this multidimensional potential energy surfaces that characterize collective phenomena such as (bio)molecular function or high-temperature superconductivity will become accessible in near future.
Quasipotential equation for hydrogen isotopes. Muonic atoms. Ground state energy levels
NASA Astrophysics Data System (ADS)
Bakalov, D.
1980-06-01
The quasipotential for the electromagnetic interaction of two particles of spin {1}/{2} or 1 with arbitrary electromagnetic interaction of two particles of spin {1}/{2} or 1 with arbitrary electromagnetic structure is constructed in the one-photon approximation. Todorov's quasipotential equation is applied to calculate the ground state energy levels of the muonic atoms pμ, dμ and tμ with accuracy 10 -3 eV.
Relativistic corrections to the ground-state energy of the positronium molecule
Bubin, Sergiy; Stanke, Monika; Kedziera, Dariusz; Adamowicz, Ludwik
2007-06-15
The leading-order relativistic corrections to the ground-state energy of the positronium molecule (Ps{sub 2}) have been computed within the framework of perturbation theory. As the zero-order wave function we used a highly accurate nonrelativistic variational expansion in terms of 6000 explicitly correlated Gaussians that yielded the lowest variational upper bound for this system to date. We also report some expectation values representing the properties of Ps{sub 2}.
Ground state energy and mass gap of a generalized quantum spin ladder
NASA Astrophysics Data System (ADS)
Batchelor, M. T.; Maslen, M.
2000-01-01
We show that a two-leg ladder Hamiltonian introduced recently by Albeverio and Fei can be made to satisfy the Hecke algebra. As a result we have found an equivalent representation of the eigenspectrum in terms of the spin- 1/2 antiferromagnetic XXZ chain at icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> = -(5/3). The values of thermodynamic quantities such as the ground state energy and mass gap follow from the known XXZ results.
Gamiz-Hernandez, Ana P; Magomedov, Artiom; Hummer, Gerhard; Kaila, Ville R I
2015-02-12
Proton-coupled electron transfer (PCET) processes are elementary chemical reactions involved in a broad range of radical and redox reactions. Elucidating fundamental PCET reaction mechanisms are thus of central importance for chemical and biochemical research. Here we use quantum chemical density functional theory (DFT), time-dependent density functional theory (TDDFT), and the algebraic diagrammatic-construction through second-order (ADC(2)) to study the mechanism, thermodynamic driving force effects, and reaction barriers of both ground state proton transfer (pT) and photoinduced proton-coupled electron transfer (PCET) between nitrosylated phenyl-phenol compounds and hydrogen-bonded t-butylamine as an external base. We show that the obtained reaction barriers for the ground state pT reactions depend linearly on the thermodynamic driving force, with a Brønsted slope of 1 or 0. Photoexcitation leads to a PCET reaction, for which we find that the excited state reaction barrier depends on the thermodynamic driving force with a Brønsted slope of 1/2. To support the mechanistic picture arising from the static potential energy surfaces, we perform additional molecular dynamics simulations on the excited state energy surface, in which we observe a spontaneous PCET between the donor and the acceptor groups. Our findings suggest that a Brønsted analysis may distinguish the ground state pT and excited state PCET processes.
Ground state spin and excitation energies in half-filled Lieb lattices
NASA Astrophysics Data System (ADS)
Ţolea, M.; Niţǎ, M.
2016-10-01
We present detailed spectral calculations for small Lieb lattices having up to N =4 number of cells, in the regime of half-filling, an instance of particular relevance for the nanomagnetism of discrete systems such as quantum dot arrays, due to the degenerate levels at midspectrum. While for the Hubbard interaction model—and even number of sites—the ground state spin is given by the Lieb theorem, the inclusion of long-range interaction—or odd number of sites—makes the spin state not known a priori, which justifies our approach. We calculate also the excitation energies, which are of experimental importance, and find significant variation induced by the interaction potential. One obtains insights on the mechanisms involved that impose as ground state the Lieb state with lower spin rather than the Hund one with maximum spin for the degenerate levels, showing this in the first and second orders of the interaction potential for the smaller lattices. The analytical results agree with the numerical ones, which are performed by exact diagonalization calculations or by a combined mean-field and configuration interaction method. While the Lieb state is always lower in energy than the Hund state, for strong long-range interaction, when possible, another minimal spin state is imposed as ground state.
Triaxiality of the ground states in the 174W
NASA Astrophysics Data System (ADS)
Ya, Tu; Chen, Y. S.; Liu, L.; Gao, Z. C.
2016-05-01
We have performed calculations for the ground states in 174W by using the projected total energy surface (PTES) calculations. Both the ground state (g.s.) band and its γ band reproduce the experimental data. Further discussion about the triaxiality in 174W has been made by transition quardrupole moment (Qt) and comparing between the PTES and TRS methods.
Calculated ground state potential surface and excitation energies for the copper trimer
NASA Technical Reports Server (NTRS)
Walch, S. P.; Laskowski, B. C.
1986-01-01
In the context of their relevance to catalysis and to materials science problems, transition metals and transition metal (TM) compounds are currently of considerable interest, and studies have been conducted of the copper trimer, Cu3. The present investigation is concerned with a study of the ground state surface and several groups of excited states in order to improve the understanding of the spectroscopy of Cu3. Differences of the current study from previous investigations are related to an employment of larger basis sets and a more extensive electron correlation. This was done with the objective to obtain a more accurate definition of the ground state surface. Features of the bonding in the copper dimer are considered to obtain a basis for an understanding of the copper trimer. Attention is given to calculational details, the ground state surface, and calculated vertical excitation energies. The results of SCF/SDCI calculations are reported for portions of the ground surface, for two groups of excited states, and for the ionization potential of Cu3.
Accurate nonrelativistic ground-state energies of 3d transition metal atoms
Scemama, A.; Applencourt, T.; Giner, E.; Caffarel, M.
2014-12-28
We present accurate nonrelativistic ground-state energies of the transition metal atoms of the 3d series calculated with Fixed-Node Diffusion Monte Carlo (FN-DMC). Selected multi-determinantal expansions obtained with the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) method and including the most prominent determinants of the full configuration interaction expansion are used as trial wavefunctions. Using a maximum of a few tens of thousands determinants, fixed-node errors on total DMC energies are found to be greatly reduced for some atoms with respect to those obtained with Hartree-Fock nodes. To the best of our knowledge, the FN-DMC/(CIPSI nodes) ground-state energies presented here are the lowest variational total energies reported so far. They differ from the recently recommended non-variational values of McCarthy and Thakkar [J. Chem. Phys. 136, 054107 (2012)] only by a few percents of the correlation energy. Thanks to the variational property of FN-DMC total energies, our results provide exact lower bounds for the absolute value of all-electron correlation energies, |E{sub c}|.
Gozem, Samer; Huntress, Mark; Schapiro, Igor; Lindh, Roland; Granovsky, Alexander A; Angeli, Celestino; Olivucci, Massimo
2012-11-13
The ground state potential energy surface of the retinal chromophore of visual pigments (e.g., bovine rhodopsin) features a low-lying conical intersection surrounded by regions with variable charge-transfer and diradical electronic structures. This implies that dynamic electron correlation may have a large effect on the shape of the force fields driving its reactivity. To investigate this effect, we focus on mapping the potential energy for three paths located along the ground state CASSCF potential energy surface of the penta-2,4-dieniminium cation taken as a minimal model of the retinal chromophore. The first path spans the bond length alternation coordinate and intercepts a conical intersection point. The other two are minimum energy paths along two distinct but kinetically competitive thermal isomerization coordinates. We show that the effect of introducing the missing dynamic electron correlation variationally (with MRCISD) and perturbatively (with the CASPT2, NEVPT2, and XMCQDPT2 methods) leads, invariably, to a stabilization of the regions with charge transfer character and to a significant reshaping of the reference CASSCF potential energy surface and suggesting a change in the dominating isomerization mechanism. The possible impact of such a correction on the photoisomerization of the retinal chromophore is discussed. PMID:26605574
An upper limit to ground state energy fluctuations in nuclear masses
Hirsch, Jorge G.; Frank, Alejandro; Barea, Jose; Velazquez, Victor; Isacker, Piet van; Zuker, Andres P.
2007-02-12
Shell model calculations are employed to estimate un upper limit of statistical fluctuations in the nuclear ground state energies. In order to mimic the presence of quantum chaos associated with neutron resonances at energies between 6 to 10 MeV, calculations include random interactions in the upper shells. The upper bound for the energy fluctuations at mid-shell is shown to have the form {sigma}(A) {approx_equal} 20A-1.34 MeV. This estimate is consistent with the mass errors found in large shell model calculations along the N=126 line, and with local mass error estimated using the Garvey-Kelson relations, all being smaller than 100 keV.
Isomeric and ground state energy level measurements of natural tellurium isotopes via (γ,n) reaction
NASA Astrophysics Data System (ADS)
Tamkas, M.; Akcali, O.; Durusoy, A.
2015-04-01
We have planned to measure isomeric and ground state energy levels in 120Te(γ,n)119m,gTe, 122Te(γ,n)121m,gTe, 128Te(γ,n)127m,gTe, 130Te(γ,n)129m,gTe photonuclear reactions of natural tellurium induced by bremsstrahlung photons with end-point energy at 18 MeV. The sample was irradiated in the clinical linear electron accelerator (Philips SLi-25) at Akdeniz University Hospital. The gamma spectrum of the tellurium sample was measured using HP(Ge) semiconductor detector (ORTEC) and multi channel analyzer. We used both MAESTRO (ORTEC) and home made root based gui program (Theia) for data analyzing. The obtained experimental data values are compared with NUDAT energy values.
QED calculation of the ground-state energy of berylliumlike ions
NASA Astrophysics Data System (ADS)
Malyshev, A. V.; Volotka, A. V.; Glazov, D. A.; Tupitsyn, I. I.; Shabaev, V. M.; Plunien, G.
2014-12-01
Ab initio QED calculations of the ground-state binding energies of berylliumlike ions are performed for the wide range of the nuclear charge number: Z =18 -96 . The calculations are carried out in the framework of the extended Furry picture starting with three different types of the screening potential. The rigorous QED calculations up to the second order of the perturbation theory are combined with the third- and higher-order electron-correlation contributions obtained within the Breit approximation by the use of the large-scale configuration-interaction Dirac-Fock-Sturm method. The effects of nuclear recoil and nuclear polarization are taken into account. The ionization potentials are obtained by subtracting the binding energies of the corresponding lithiumlike ions. In comparison with the previous calculations the accuracy of the binding energies and the ionization potentials is significantly improved.
Energy splitting of the ground-state doublet in the nucleus 229Th.
Beck, B R; Becker, J A; Beiersdorfer, P; Brown, G V; Moody, K J; Wilhelmy, J B; Porter, F S; Kilbourne, C A; Kelley, R L
2007-04-01
The energy splitting of the 229Th ground-state doublet is measured to be 7.6+/-0.5 eV, significantly greater than earlier measurements. Gamma rays produced following the alpha decay of 233U (105 muCi) were counted in the NASA/electron beam ion trap x-ray microcalorimeter spectrometer with an experimental energy resolution of 26 eV (FWHM). A difference technique was applied to the gamma-ray decay of the 71.82 keV level that populates both members of the doublet. A positive correction amounting to 0.6 eV was made for the unobserved interband decay of the 29.19 keV state (29.19-->0 keV).
Energy Splitting of the Ground-State Doublet in the Nucleus Th229
NASA Astrophysics Data System (ADS)
Beck, B. R.; Becker, J. A.; Beiersdorfer, P.; Brown, G. V.; Moody, K. J.; Wilhelmy, J. B.; Porter, F. S.; Kilbourne, C. A.; Kelley, R. L.
2007-04-01
The energy splitting of the Th229 ground-state doublet is measured to be 7.6±0.5eV, significantly greater than earlier measurements. Gamma rays produced following the alpha decay of U233 (105μCi) were counted in the NASA/electron beam ion trap x-ray microcalorimeter spectrometer with an experimental energy resolution of 26 eV (FWHM). A difference technique was applied to the gamma-ray decay of the 71.82 keV level that populates both members of the doublet. A positive correction amounting to 0.6 eV was made for the unobserved interband decay of the 29.19 keV state (29.19→0keV).
NASA Astrophysics Data System (ADS)
Ibral, Asmaa; Zouitine, Asmae; Assaid, El Mahdi; Feddi, El Mustapha; Dujardin, Francis
2014-09-01
Ground state energy and wave function of a hydrogen-like off-centre donor impurity, confined anywhere in a ZnS/CdSe spherical core/shell nanostructure are determined in the framework of the envelope function approximation. Conduction band-edge alignment between core and shell of nanostructure is described by a finite height barrier. Dielectric constant mismatch at the surface where core and shell materials meet is taken into account. Electron effective mass mismatch at the inner surface between core and shell is considered. A trial wave function where coulomb attraction between electron and off-centre ionized donor is used to calculate ground state energy via the Ritz variational principle. The numerical approach developed enables access to the dependence of binding energy, coulomb correlation parameter, spatial extension and radial probability density with respect to core radius, shell radius and impurity position inside ZnS/CdSe core/shell nanostructure.
Scaling of the ground-state energy of relativistic ions in high locally bounded magnetic fields
Jakubassa-Amundsen, D. H.
2010-08-15
We consider the pseudorelativistic Chandrasekhar/Herbst operator h{sup H} for the description of relativistic one-electron ions in a locally bounded magnetic field. We show that for Coulomb potentials of strength {gamma}<2/{pi}, the spectrum of h{sup H} is discrete below m (the electron mass). For magnetic fields in the class B{sub A}(x)=B{center_dot}(1+{tau}/2)(|x{sub 1}|{sup {tau}+}|x{sub 2}|{sup {tau}})e{sub z}, the ground-state energy of h{sup H} decreases according to B{sup 1}/(2+{tau}) as B{yields}{infinity} for 0{<=}{tau}<{tau}{sub c}, where {tau}{sub c} is some critical value, depending on {gamma}.
NASA Technical Reports Server (NTRS)
Wilson, L. W.
1974-01-01
The present work investigates analytically the effect of an intermediate or intense magnetic field, such as probably exist in white dwarfs and near pulsars, on the binding energy of the hydrogen ground state. A wave-function 'prescription' is given for an analytic variational calculation of the binding energy. The calculation still gives a smooth transition between intermediate and intense fields. An explicit calculation of the ground-state binding energy as B goes to infinity is provided for the Yafet et al. (1956) trial function.
Covariant energy density functionals: Nuclear matter constraints and global ground state properties
NASA Astrophysics Data System (ADS)
Afanasjev, A. V.; Agbemava, S. E.
2016-05-01
The correlations between global description of the ground state properties (binding energies, charge radii) and nuclear matter properties of the state-of-the-art covariant energy density functionals have been studied. It was concluded that the strict enforcement of the constraints on the nuclear matter properties (NMP) defined in Dutra et al. [Phys. Rev. C 90, 055203 (2014), 10.1103/PhysRevC.90.055203] will not necessarily lead to the functionals with good description of the binding energies and other ground and excited state properties. In addition, it will not substantially reduce the uncertainties in the predictions of the binding energies in neutron-rich systems. It turns out that the functionals, which come close to satisfying these NMP constraints, have some problems in the description of existing data. On the other hand, these problems are either absent or much smaller in the functionals which are carefully fitted to finite nuclei but which violate some NMP constraints. This is a consequence of the fact that the properties of finite nuclei are defined not only by nuclear matter properties but also by underlying shell effects. The mismatch of phenomenological content, existing in all modern functionals, related to nuclear matter physics and the physics of finite nuclei could also be responsible.
Accurate Determination of Rotational Energy Levels in the Ground State of ^{12}CH_4
NASA Astrophysics Data System (ADS)
Abe, M.; Iwakuni, K.; Okubo, S.; Sasada, H.
2013-06-01
We have measured absolute frequencies of saturated absorption of 183 allowed and 21 forbidden transitions in the νb{3} band of ^{12}CH_4 using an optical comb-referenced difference-frequency-generation spectrometer from 86.8 to 93.1 THz (from 2890 to 3100 wn). The pump and signal sources are a 1.06-μ m Nd:YAG laser and a 1.5-μ m extended-cavity laser diode. An enhanced-cavity absorption cell increases the optical electric field and enhances the sensitivity. The typical uncertainty is 3 kHz for the allowed transitions and 12 kHz for the forbidden transitions. Twenty combination differences are precisely determined, and the scalar rotational and centrifugal distortion constants of the ground state are thereby yielded as r@ = l@ r@ = l B_{{s}} (157 122 614.2 ± 1.5) kHz, D_{{s}} (3 328.545 ± 0.031) kHz, H_{{s}} (190.90 ± 0.26) Hz, and L_{{s}} (-13.16 ± 0.76) mHz. Here, B_{{s}} is the rotational constant and D_{{s}}, H_{{s}} and L_{{s}} are the scalar quartic, sextic, octic distortion constants. The relative uncertainties are considerably smaller than those obtained from global analysis of Fourier-transform infrared spectroscopy. S. Okubo, H. Nakayama, K. Iwakuni, H. Inaba and H. Sasada, Opt. Express 19, 23878 (2011). M. Abe, K. Iwakuni, S. Okubo, and H. Sasada, J. Opt. Soc. Am. B (to be published). S. Albert, S. Bauerecker, V. Boudon, L. R. Brown, J. -P. Champion, M. Loëte, A. Nikitin, and M. Quack, Chem. Phys. 356, 131 (2009).
Theoretical Electric Dipole Moments and Dissociation Energies for the Ground States of GaH-BrH
NASA Technical Reports Server (NTRS)
Pettersson, Lars G. M.; Langhoff, Stephen R.
1986-01-01
Reliable experimental diople moments are available for the ground states of SeH and BrH whereas no values have been reported for GaH and AsH a recently reported experimental dipole moment for GeH of 1.24 + or -0.01 D has been seriously questioned, and a much lower value of, 0.1 + or - 0.05 D, suggested. In this work, we report accurate theoretical dipole moments, dipole derivatives, dissociation energies, and spectroscopic constants (tau(sub e), omega(sub e)) for the ground states of GaH through BrH.
NASA Astrophysics Data System (ADS)
Sharp, P. M.; D'Amico, I.
2016-02-01
We consider a model system of two electrons confined in a two-dimensional harmonic oscillator potential, with the electrons interacting via an α / r2 potential, and subject to a magnetic field applied perpendicular to the plane of confinement. Our results show that variations in the strength of the electron-electron interaction generate a "band structure" in ground state metric spaces, which shares many characteristics with those generated as a result of varying the confinement potential. In particular, the metric spaces for wavefunctions, particle densities, and paramagnetic current densities all exhibit distinct "bands" and "gaps". The behavior of the polar angle of the bands also shares traits with that obtained by varying the confinement potential, but the behavior of the arc lengths of the bands on the metric space spheres can be seen to be different for the two cases and opposite for a large range of angular momentum values. The findings here and in Refs. [1,2] demonstrate that the "band structure" that arises in ground state metric spaces when a magnetic field is applied is a robust feature.
ERIC Educational Resources Information Center
Harbola, Varun
2011-01-01
In this paper, we accurately estimate the ground-state energy and the atomic radius of the helium atom and a helium-like Hookean atom by employing the uncertainty principle in conjunction with the variational approach. We show that with the use of the uncertainty principle, electrons are found to be spread over a radial region, giving an electron…
Koput, Jacek
2015-06-30
The accurate ground-state potential energy function of imidogen, NH, has been determined from ab initio calculations using the multireference averaged coupled-pair functional (MR-ACPF) method in conjunction with the correlation-consistent core-valence basis sets up to octuple-zeta quality. The importance of several effects, including electron correlation beyond the MR-ACPF level of approximation, the scalar relativistic, adiabatic, and nonadiabatic corrections were discussed. Along with the large one-particle basis set, all of these effects were found to be crucial to attain "spectroscopic" accuracy of the theoretical predictions of vibration-rotation energy levels of NH.
Face-dependent Auger neutralization and ground-state energy shift for He in front of Al surfaces
Wethekam, S.; Winter, H.; Valdes, Diego; Monreal, R. C.
2008-08-15
He atoms and ions with keV energies are scattered under grazing angles of incidence from Al(111), Al(100), and Al(110) surfaces. Fractions of surviving ions and normal energy gains of He{sup +} ions prior to neutralization, derived from shifts of angular distributions for incident atoms and ions, are compared to results from three-dimensional Monte Carlo simulations based on theoretically calculated Auger neutralization rates and He ground-state energy shifts. From the good agreement of experimental data with simulations, we conclude a detailed microscopic understanding for a model system of ion-surface interactions. Our work provides further evidence for the recently reported surface Miller index dependence for the neutralization of He{sup +} ions at metal surfaces. The study is extended to the face dependence of the He ground-state energy shift.
NASA Astrophysics Data System (ADS)
Aftalion, Amandine; Mason, Peter
2016-08-01
We classify the ground states and topological defects of two-component Bose-Einstein condensates under the effect of internal coherent Rabi coupling. We present numerical phase diagrams which show the boundaries between symmetry-breaking components and various vortex patterns (triangular, square, bound state between vortices). We estimate the Rabi energy in the Thomas-Fermi limit which allows us to have an analytical description of the point energy leading to the formation of the various vortex patterns.
NASA Astrophysics Data System (ADS)
Tasinato, Nicola; Turchetto, Arianna; Puzzarini, Cristina; Stoppa, Paolo; Pietropolli Charmet, Andrea; Giorgianni, Santi
2014-09-01
Hydrofluorocarbons have been used as replacement gases of chlorofluorocarbons, since the latter have been phased out by the Montreal Protocol due to their environmental hazardous ozone-depleting effects. This is also the case of difluoromethane (CH2F2, HFC-32), which nowadays is widely used in refrigerant mixtures together with CF3CH3, CF3CH2F, and CF3CHF2. Due to its commercial use, in the last years, the atmospheric concentration of HFC-32 has increased significantly. However, this molecule presents strong absorptions within the 8-12 μm atmospheric window, and hence it is a greenhouse gas which contributes to global warming. Although over the years several experimental and theoretical investigations dealt with the spectroscopic properties of CH2F2, up to now pressure broadening coefficients have never been determined. In the present work, the line-by-line parameters of CH2F2 are retrieved for either ground state or ν7 band transitions by means of microwave (MW) and infrared (IR) absorption spectroscopy, respectively. In particular, laboratory experiments are carried out on 9 pure rotational transitions of the ground state and 26 ro-vibrational transitions belonging to the ν7 band lying around 8.2 μm within the atmospheric region. Measurements are carried out at room temperature on self-perturbed CH2F2 as well as on CH2F2 perturbed by N2 and O2. The line shape analysis leads to the first determination of self-, N2-, O2-, and air-broadening coefficients, and also of line intensities (IR). Upon comparison, broadening coefficients of ground state transitions are larger than those of the ν7 band, and no clear dependence on the rotational quantum numbers can be reported. The obtained results represent basic information for the atmospheric modelling of this compound as well as for remote sensing applications.
Sims, James S.; Hagstrom, Stanley A.
2014-06-14
In a previous work, Sims and Hagstrom [“Hylleraas-configuration-interaction study of the 1 {sup 1}S ground state of neutral beryllium,” Phys. Rev. A 83, 032518 (2011)] reported Hylleraas-configuration-interaction (Hy-CI) method variational calculations for the {sup 1}S ground state of neutral beryllium with an estimated accuracy of a tenth of a microhartree. In this work, the calculations have been extended to higher accuracy and, by simple scaling of the orbital exponents, to the entire Be 2 {sup 1}S isoelectronic sequence. The best nonrelativistic energies for Be, B{sup +}, and C{sup ++} obtained are −14.6673 5649 269, −24.3488 8446 36, and −36.5348 5236 25 hartree, respectively. Except for Be, all computed nonrelativistic energies are superior to the known reference energies for these states.
Jahan K, Luhluh Boda, Aalu; Chatterjee, Ashok
2015-05-15
The problem of an exciton trapped in a three dimensional Gaussian quantum dot is studied in the presence of an external magnetic field. A variational method is employed to obtain the ground state energy of the exciton as a function of the quantum dot size, the confinement strength and the magnetic field. It is also shown that the variation of the size of the exciton with the radius of the quantum dot.
Loco, Daniele; Polack, Étienne; Caprasecca, Stefano; Lagardère, Louis; Lipparini, Filippo; Piquemal, Jean-Philip; Mennucci, Benedetta
2016-08-01
A fully polarizable implementation of the hybrid quantum mechanics/molecular mechanics approach is presented, where the classical environment is described through the AMOEBA polarizable force field. A variational formalism, offering a self-consistent relaxation of both the MM induced dipoles and the QM electronic density, is used for ground state energies and extended to electronic excitations in the framework of time-dependent density functional theory combined with a state specific response of the classical part. An application to the calculation of the solvatochromism of the pyridinium N-phenolate betaine dye used to define the solvent ET(30) scale is presented. The results show that the QM/AMOEBA model not only properly describes specific and bulk effects in the ground state but it also correctly responds to the large change in the solute electronic charge distribution upon excitation.
Loco, Daniele; Polack, Étienne; Caprasecca, Stefano; Lagardère, Louis; Lipparini, Filippo; Piquemal, Jean-Philip; Mennucci, Benedetta
2016-08-01
A fully polarizable implementation of the hybrid quantum mechanics/molecular mechanics approach is presented, where the classical environment is described through the AMOEBA polarizable force field. A variational formalism, offering a self-consistent relaxation of both the MM induced dipoles and the QM electronic density, is used for ground state energies and extended to electronic excitations in the framework of time-dependent density functional theory combined with a state specific response of the classical part. An application to the calculation of the solvatochromism of the pyridinium N-phenolate betaine dye used to define the solvent ET(30) scale is presented. The results show that the QM/AMOEBA model not only properly describes specific and bulk effects in the ground state but it also correctly responds to the large change in the solute electronic charge distribution upon excitation. PMID:27340904
Adame, J.; Warzel, S.
2015-11-15
In this note, we use ideas of Farhi et al. [Int. J. Quantum. Inf. 6, 503 (2008) and Quantum Inf. Comput. 11, 840 (2011)] who link a lower bound on the run time of their quantum adiabatic search algorithm to an upper bound on the energy gap above the ground-state of the generators of this algorithm. We apply these ideas to the quantum random energy model (QREM). Our main result is a simple proof of the conjectured exponential vanishing of the energy gap of the QREM.
Ground-state properties of the periodic Anderson model
NASA Technical Reports Server (NTRS)
Blankenbecler, R.; Fulco, J. R.; Gill, W.; Scalapino, D. J.
1987-01-01
The ground-state energy, hybridization matrix element, local moment, and spin-density correlations of a one-dimensional, finite-chain, periodic, symmetric Anderson model are obtained by numerical simulations and compared with perturbation theory and strong-coupling results. It is found that the local f-electron spins are compensated by correlation with other f-electrons as well as band electrons leading to a nonmagnetic ground state.
Ground-state-energy theorem and the virial theorem of a many-particle system in d dimensions
NASA Technical Reports Server (NTRS)
Iwamoto, N.
1984-01-01
The equivalence of Pauli's ground-state-energy theorem and the virial theorem is demonstrated for a many-particle system interacting with an interparticle potential in d dimensions at zero and finite temperatures. Pauli's theorem has an integral form in which the variable is the coupling constant e-squared, while the virial theorem has a differential form in which the variable has the number density n. The essence of the equivalence proof consists in changing the variable from n to e-squared by noting the dependence of the excess free energy on dimensionless quantities for zero-temperature and classical cases.
The Ground State of a Gross-Pitaevskii Energy with General Potential in the Thomas-Fermi Limit
NASA Astrophysics Data System (ADS)
Karali, Georgia; Sourdis, Christos
2015-08-01
We study the ground state which minimizes a Gross-Pitaevskii energy with general non-radial trapping potential, under the unit mass constraint, in the Thomas-Fermi limit where a small parameter tends to 0. This ground state plays an important role in the mathematical treatment of recent experiments on the phenomenon of Bose-Einstein condensation, and in the study of various types of solutions of nonhomogeneous defocusing nonlinear Schrödinger equations. Many of these applications require delicate estimates for the behavior of the ground state near the boundary of the condensate, as , in the vicinity of which the ground state has irregular behavior in the form of a steep corner layer. In particular, the role of this layer is important in order to detect the presence of vortices in the small density region of the condensate, to understand the superfluid flow around an obstacle, and it also has a leading order contribution in the energy. In contrast to previous approaches, we utilize a perturbation argument to go beyond the classical Thomas-Fermi approximation and accurately approximate the layer by the Hastings-McLeod solution of the Painlevé-II equation. This settles an open problem (cf. Aftalion in Vortices in Bose Einstein Condensates. Birkhäuser Boston, Boston, 2006, pg. 13 or Open Problem 8.1), answered very recently only for the special case of the model harmonic potential (Gallo and Pelinovsky in Asymptot Anal 73:53-96, 2011). In fact, we even improve upon previous results that relied heavily on the radial symmetry of the potential trap. Moreover, we show that the ground state has the maximal regularity available, namely it remains uniformly bounded in the -Hölder norm, which is the exact Hölder regularity of the singular limit profile, as . Our study is highly motivated by an interesting open problem posed recently by A ftalion, Jerrard, and R oyo-L etelier (J Funct Anal 260:2387-2406 2011), and an open question of G allo and P elinovsky (J Math Anal
Incremental expansions for the ground-state energy of the two-dimensional Hubbard model
Malek, J.; Flach, S.; Kladko, K.
1999-02-01
A generalization of Faddeev{close_quote}s approach of the three-body problem to the many-body problem leads to the method of increments. This method was recently applied to account for the ground-state properties of Hubbard-Peierls chains [J. Malek, K. Kladko, and S. Flach, JETP Lett. {bold 67}, 1052 (1998)]. Here we generalize this approach to two-dimensional square lattices and explicitly treat the incremental expansion up to third order. Comparing our numerical results with various other approaches (Monte Carlo, cumulant approaches) we show that incremental expansions are very efficient because good accuracy with these approaches is achieved treating lattice segments composed of eight sites only. {copyright} {ital 1999} {ital The American Physical Society}
Ground-state energy of a quantum chain with competing interactions
NASA Astrophysics Data System (ADS)
Carneiro, C. E. I.; de Oliveira, M. J.; Wreszinski, W. F.
1995-04-01
We show rigorously that the ground state of a quantum chain with competing ferromagnetic nearest and antiferromagnetic next nearest interactions undergoes a transition from ferromagnetic to helical type, in the isotropic case, for a certain value of the relevant ratio of coupling constants. Boundaries of the phase diagram are also determined in the anisotropic case. The stability of a special quantum state (corresponding to a classical modulated phase of ⫇=п/3) is analyzed by an extension of Holstein-Primakoff arguments, along a line of constant ratio of couplings, showing in particular a sequence of (instability) gaps. Finally, a natural adaptation of a variational wave function due to Huse and Elser is used to study several portions of the phase diagram, with very good agreement with previous theoretical results.
NASA Astrophysics Data System (ADS)
Zeng, Hui; Zhao, Jun
2012-07-01
In this paper, the energy, equilibrium geometry, and harmonic frequency of the ground electronic state of PO2 are computed using the B3LYP, B3P86, CCSD(T), and QCISD(T) methods in conjunction with the 6-311++G(3df, 3pd) and cc-pVTZ basis sets. A comparison between the computational results and the experimental values indicates that the B3P86/6-311++G(3df, 3pd) method can give better energy calculation results for the PO2 molecule. It is shown that the ground state of the PO2 molecule has C2ν symmetry and its ground electronic state is X2A1. The equilibrium parameters of the structure are RP-O = 0.1465 nm, ∠OPO = 134.96°, and the dissociation energy is Ed = 19.218 eV. The bent vibrational frequency ν1 = 386 cm-1, symmetric stretching frequency ν2 = 1095 cm-1, and asymmetric stretching frequency ν3 = 1333 cm-1 are obtained. On the basis of atomic and molecular reaction statics, a reasonable dissociation limit for the ground state of the PO2 molecule is determined. Then the analytic potential energy function of the PO2 molecule is derived using many-body expansion theory. The potential curves correctly reproduce the configurations and the dissociation energy for the PO2 molecule.
Boda, Aalu Kumar, D. Sanjeev; Chatterjee, Ashok; Mukhopadhyay, Soma
2015-06-24
The ground state energy of a hydrogenic D{sup 0} complex trapped in a three-dimensional GaAs quantum dot with Gaussian confinement is calculated variationally incorporating the effect of Rashba spin-orbit interaction. The results are obtained as a function of the quantum dot size and the Rashba spin-orbit interaction. The results show that the Rashba interaction reduces the ground state energy of the system.
NASA Astrophysics Data System (ADS)
Paul, Susobhan; Ghosh, Asim Kumar
2014-08-01
The ground state energy and the spin gap of a spin-12 Heisenberg antiferromagnetic XXZ chain in the presence of longitudinal staggered field (hz) have been estimated by using Jordan-Wigner representation, exact diagonalization and perturbative analysis. All those quantities have been obtained for a region of anisotropic parameter (Δ) defined by 0≤Δ≤1. For Δ=0, the exact value of ground state energy is found for finite values of hz. The spin gap is found to develop as soon as the staggered field is switched on. The magnitude of spin gap is compared with the field induced gap measured in magnetic compounds CuBenzoate and Yb4As3 when Δ=1. The dependence of spin gap on both Δ and hz has been found which gives rise to scaling laws associated with hz. Scaling exponents obtained in two different cases show excellent agreements with the previously determined values. The variation of scaling exponents with Δ can be fitted with a regular function.
Gonzalez, M. G.; Rodriguez, J. D.; Rubio-Lago, L.; Banares, L.
2011-07-14
The photodissociation of CH{sub 3}I in the second absorption band (the B-band) has been studied at the wavelength 199.11 nm, coincident with the 3{sub 0}{sup 1} {sup 3}R{sub 1}(E)(leftarrow)X(tilde sign)({sup 1}A{sub 1}) CH{sub 3}I vibronic transition, using a combination of slice imaging and resonance enhanced multiphoton ionization detection of the CH{sub 3} fragment. The kinetic energy and angular distributions of the recoiling CH{sub 3} fragment confirm a major predissociation dynamics channel as a result of the interaction between the bound {sup 3}R{sub 1} Rydberg state and the repulsive {sup 3}A{sub 1}(E) state - ascribed to the A-band - yielding CH{sub 3} fragments in correlation with spin-orbit excited I*({sup 2}P{sub 1/2}) atoms. In addition, first evidence of a non-negligible population of ground state I({sup 2}P{sub 3/2}) atoms in the CH{sub 3} fragment slice images, suggests a secondary predissociation mechanism via interaction between the {sup 3}R{sub 1} Rydberg state and the repulsive A-band {sup 1}Q{sub 1} state.
Li, Y Q; Zhang, P Y; Han, K L
2015-03-28
A global many-body expansion potential energy surface is reported for the electronic ground state of CH2 (+) by fitting high level ab initio energies calculated at the multireference configuration interaction level with the aug-cc-pV6Z basis set. The topographical features of the new global potential energy surface are examined in detail and found to be in good agreement with those calculated directly from the raw ab initio energies, as well as previous calculations available in the literature. In turn, in order to validate the potential energy surface, a test theoretical study of the reaction CH(+)(X(1)Σ(+))+H((2)S)→C(+)((2)P)+H2(X(1)Σg (+)) has been carried out with the method of time dependent wavepacket on the title potential energy surface. The total integral cross sections and the rate coefficients have been calculated; the results determined that the new potential energy surface can both be recommended for dynamics studies of any type and as building blocks for constructing the potential energy surfaces of larger C(+)/H containing systems.
NASA Astrophysics Data System (ADS)
Ho, Yew Kam; Lin, Yen-Chang
2016-05-01
Correlation energy of a quantum system is defined as the difference between its exact energy Eex, and its Hartree-Fock energy EHF. In a recent related development, entanglement measures can be quantified with von Neumann entropy SvN(ρ) = - Tr(ρlog2 ρ) or linear entropy SL(ρ) = 1 - Tr(ρ2) , where ρ is the one-particle reduced density matrix, and Tr(ρ2) is defined as the purity of state. In the present work we calculate SL and SvN for the ground 1s21 S states in helium-like ions for Z = 2 to 15, using configuration interaction (CI) with B-Spline basis up to about 6000 terms to construct the wave functions, and with which density matrix, linear and von Neumann entropies are calculated. We have found close relationship between the reduced correlation energy, defined as Ecorr = (ECI- EHF) /ECI (with ECI being our calculated energy), and SL or SvN. Our results support Collins conjecture that there is a linear relationship between correlation energy and entanglement entropy, i.e., Ecorr = CS, where C is called Collins constant. Using the calculated ground state energies for Z = 2 to Z = 15, and the entanglement measured with linear entropy SL for such states, C is determined as 0.90716. At the meeting, we will present result for Collins constant determined from von Neumann entropy, and details of our calculations. This work was supported by the MOST in Taiwan.
Levy, Mel E-mail: mlevy@tulane.edu; Anderson, James S. M.; Zadeh, Farnaz Heidar; Ayers, Paul W. E-mail: mlevy@tulane.edu
2014-05-14
Properties of exact density functionals provide useful constraints for the development of new approximate functionals. This paper focuses on convex sums of ground-level densities. It is observed that the electronic kinetic energy of a convex sum of degenerate ground-level densities is equal to the convex sum of the kinetic energies of the individual degenerate densities. (The same type of relationship holds also for the electron-electron repulsion energy.) This extends a known property of the Levy-Valone Ensemble Constrained-Search and the Lieb Legendre-Transform refomulations of the Hohenberg-Kohn functional to the individual components of the functional. Moreover, we observe that the kinetic and electron-repulsion results also apply to densities with fractional electron number (even if there are no degeneracies), and we close with an analogous point-wise property involving the external potential. Examples where different degenerate states have different kinetic energy and electron-nuclear attraction energy are given; consequently, individual components of the ground state electronic energy can change abruptly when the molecular geometry changes. These discontinuities are predicted to be ubiquitous at conical intersections, complicating the development of universally applicable density-functional approximations.
Analytical expressions for partial wave two-body Coulomb transition matrices at ground-state energy
NASA Astrophysics Data System (ADS)
Kharchenko, V. F.
2016-11-01
Leaning upon the Fock method of the stereographic projection of the three-dimensional momentum space onto the four-dimensional unit sphere the possibility of the analytical solving of the Lippmann-Schwinger integral equation for the partial wave two-body Coulomb transition matrix at the ground bound state energy has been studied. In this case new expressions for the partial p-, d- and f-wave two-body Coulomb transition matrices have been obtained in the simple analytical form. The developed approach can also be extended to determine analytically the partial wave Coulomb transition matrices at the energies of excited bound states.
Badri, Zahra; Foroutan-Nejad, Cina
2016-04-28
In the present account we investigate a theoretical link between the bond length, electron sharing, and bond energy within the context of quantum chemical topology theories. The aromatic stabilization energy, ASE, was estimated from this theoretical link without using isodesmic reactions for the first time. The ASE values obtained from our method show a meaningful correlation with the number of electrons contributing to the aromaticity. This theoretical link demonstrates that structural, electronic, and energetic criteria of aromaticity - ground-state aromaticity - belong to the same class and guarantees that they assess the same property as aromaticity. Theory suggests that interatomic exchange-correlation potential, obtained from the theory of Interacting Quantum Atoms (IQA), is linearly connected to the delocalization index of Quantum Theory of Atoms in Molecules (QTAIM) and the bond length through a first order approximation. Our study shows that the relationship between energy, structure and electron sharing marginally deviates from the ideal linear form expected from the first order approximation. The observed deviation from linearity was attributed to a different contribution of exchange-correlation to the bond energy for the σ- and π-frameworks. Finally, we proposed two-dimensional energy-structure-based aromaticity indices in analogy to the electron sharing indices of aromaticity. PMID:26678719
Badri, Zahra; Foroutan-Nejad, Cina
2016-04-28
In the present account we investigate a theoretical link between the bond length, electron sharing, and bond energy within the context of quantum chemical topology theories. The aromatic stabilization energy, ASE, was estimated from this theoretical link without using isodesmic reactions for the first time. The ASE values obtained from our method show a meaningful correlation with the number of electrons contributing to the aromaticity. This theoretical link demonstrates that structural, electronic, and energetic criteria of aromaticity - ground-state aromaticity - belong to the same class and guarantees that they assess the same property as aromaticity. Theory suggests that interatomic exchange-correlation potential, obtained from the theory of Interacting Quantum Atoms (IQA), is linearly connected to the delocalization index of Quantum Theory of Atoms in Molecules (QTAIM) and the bond length through a first order approximation. Our study shows that the relationship between energy, structure and electron sharing marginally deviates from the ideal linear form expected from the first order approximation. The observed deviation from linearity was attributed to a different contribution of exchange-correlation to the bond energy for the σ- and π-frameworks. Finally, we proposed two-dimensional energy-structure-based aromaticity indices in analogy to the electron sharing indices of aromaticity.
Sims, James S; Hagstrom, Stanley A
2006-03-01
Born-Oppenheimer approximation Hylleraas variational calculations with up to 7034 expansion terms are reported for the 1sigma(g)+ ground state of neutral hydrogen at various internuclear distances. The nonrelativistic energy is calculated to be -1.174 475 714 220(1) hartree at R = 1.4 bohr, which is four orders of magnitude better than the best previous Hylleraas calculation, that of Wolniewicz [J. Chem. Phys. 103, 1792 (1995)]. This result agrees well with the best previous variational energy, -1.174 475 714 216 hartree, of Cencek (personal communication), obtained using explicitly correlated Gaussians (ECGs) [Cencek and Rychlewski, J. Chem. Phys. 98, 1252 (1993); Cencek et al., ibid. 95, 2572 (1995); Rychlewski, Adv. Quantum Chem. 31, 173 (1998)]. The uncertainty in our result is also discussed. The nonrelativistic energy is calculated to be -1.174 475 931 399(1) hartree at the equilibrium R = 1.4011 bohr distance. This result also agrees well with the best previous variational energy, -1.174 475 931 389 hartree, of Cencek and Rychlewski [Rychlewski, Handbook of Molecular Physics and Quantum Chemistry, edited by S. Wilson (Wiley, New York, 2003), Vol. 2, pp. 199-218; Rychlewski, Explicitly Correlated Wave Functions in Chemistry and Physics Theory and Applications, edited by J. Rychlewski (Kluwer Academic, Dordrecht, 2003), pp. 91-147.], obtained using ECGs. PMID:16526839
Ground-state binding energy of H4Λ from high-resolution decay-pion spectroscopy
NASA Astrophysics Data System (ADS)
Schulz, F.; Achenbach, P.; Aulenbacher, S.; Beričič, J.; Bleser, S.; Böhm, R.; Bosnar, D.; Correa, L.; Distler, M. O.; Esser, A.; Fonvieille, H.; Friščić, I.; Fujii, Y.; Fujita, M.; Gogami, T.; Kanda, H.; Kaneta, M.; Kegel, S.; Kohl, Y.; Kusaka, W.; Margaryan, A.; Merkel, H.; Mihovilovič, M.; Müller, U.; Nagao, S.; Nakamura, S. N.; Pochodzalla, J.; Sanchez Lorente, A.; Schlimme, B. S.; Schoth, M.; Sfienti, C.; Širca, S.; Steinen, M.; Takahashi, Y.; Tang, L.; Thiel, M.; Tsukada, K.; Tyukin, A.; Weber, A.
2016-10-01
A systematic study on the Λ ground state binding energy of hyperhydrogen H4Λ measured at the Mainz Microtron MAMI is presented. The energy was deduced from the spectroscopy of mono-energetic pions from the two-body decays of hyperfragments, which were produced and stopped in a 9Be target. First data, taken in the year 2012 with a high resolution magnetic spectrometer, demonstrated an almost one order of magnitude higher precision than emulsion data, while being limited by systematic uncertainties. In 2014 an extended measurement campaign was performed with improved control over systematic effects, increasing the yield of hypernuclei and confirming the observation with two independent spectrometers and two targets of different thicknesses. The analysis of these data is in agreement with the previously published value for the H4Λ binding energy as well as with a consistent re-analysis of the 2012 data. When compared to the He4Λ binding energy from emulsion data, a large charge symmetry breaking effect in the A = 4 hypernuclear system is confirmed.
NASA Astrophysics Data System (ADS)
Sims, James S.; Hagstrom, Stanley A.
2006-03-01
Born-Oppenheimer approximation Hylleraas variational calculations with up to 7034 expansion terms are reported for the Σg+1 ground state of neutral hydrogen at various internuclear distances. The nonrelativistic energy is calculated to be -1.174475714220(1)hartree at R =1.4bohr, which is four orders of magnitude better than the best previous Hylleraas calculation, that of Wolniewicz [J. Chem. Phys. 103, 1792 (1995)]. This result agrees well with the best previous variational energy, -1.174475714216hartree, of Cencek (personal communication), obtained using explicitly correlated Gaussians (ECGs) [Cencek and Rychlewski, J. Chem. Phys. 98, 1252 (1993); Cencek et al., ibid. 95, 2572 (1995); Rychlewski, Adv. Quantum Chem. 31, 173 (1998)]. The uncertainty in our result is also discussed. The nonrelativistic energy is calculated to be -1.174475931399(1)hartree at the equilibrium R =1.4011bohr distance. This result also agrees well with the best previous variational energy, -1.174475931389hartree, of Cencek and Rychlewski [Rychlewski, Handbook of Molecular Physics and Quantum Chemistry, edited by S. Wilson (Wiley, New York, 2003), Vol. 2, pp. 199-218; Rychlewski, Explicitly Correlated Wave Functions in Chemistry and Physics Theory and Applications, edited by J. Rychlewski (Kluwer Academic, Dordrecht, 2003), pp. 91-147.], obtained using ECGs.
Nonadiabatic couplings in low-energy collisions of hydrogen ground-state atoms
Wolniewicz, L.
2003-10-01
The effect of nonadiabatic couplings on low-energy s-wave scattering of two hydrogen atoms is investigated. Coupling matrix elements are computed in a wide range of internuclear distances. The resulting scattering equations are numerically unstable and therefore are integrated only approximately. Computations are performed for H, D, and T atoms. The phase shifts in the zero velocity limit are inversely proportional to the nuclear reduced mass {delta}{sub 0}{approx_equal}0.392/{mu}. This leads to infinite scattering lengths.
NASA Astrophysics Data System (ADS)
Koh, Yang Wei
2016-04-01
We present an extensive numerical study of the Sherrington-Kirkpatrick model in a transverse field. Recent numerical studies of quantum spin glasses have focused on exact diagonalization of the full Hamiltonian for small systems (≈20 spins). However, such exact numerical treatments are difficult to apply on larger systems. We propose making an approximation by using only a subspace of the full Hilbert space spanned by low-lying excitations consisting of one-spin-flipped and two-spin-flipped states. The approximation procedure is carried out within the theoretical framework of the Hartree-Fock approximation and configuration interaction. Although not exact, our approach allows us to study larger system sizes comparable to that achievable by state-of-the-art quantum Monte Carlo simulations. We calculate two quantities of interest due to recent advances in quantum annealing, the ground-state energy and the energy gap between the ground and first excited states. For the energy gap, we derive a formula that enables it to be calculated using just the ground-state wave function, thereby circumventing the need to diagonalize the Hamiltonian. We calculate the scalings of the energy gap and the leading correction to the extensive part of the ground-state energy with system size, which are difficult to obtain with current methods.
NASA Technical Reports Server (NTRS)
Partridge, Harry; Stallcop, James R.; Levin, Eugene; Arnold, Jim (Technical Monitor)
2001-01-01
The interactions of a He atom with a heavier atom are examined for 26 different elements, which are consecutive members selected from three rows (Li - Ne, Na - Ar, and K,Ca, Ga - Kr) and column 12 (Zn,Cd) of the periodic table. Interaction energies are determined wing high-quality ab initio calculations for the states of the molecule that would be formed from each pair of atoms in their ground states. Potential energies are tabulated for a broad range of Interatomic separation distances. The results show, for example, that the energy of an alkali interaction at small separations is nearly the same as that of a rare-gas interaction with the same electron configuration for the dosed shells. Furthermore, the repulsive-range parameter for this region is very short compared to its length for the repulsion dominated by the alkali-valence electron at large separations (beyond about 3-4 a(sub 0)). The potential energies in the region of the van der Waals minimum agree well with the most accurate results available. The ab initio energies are applied to calculate scattering cross sections and obtain the collision integrals that are needed to determine transport properties to second order. The theoretical values of Li-He total scattering cross sections and the rare-gas atom-He transport properties agree well (to within about 1%) with the corresponding measured data. Effective potential energies are constructed from the ab initio energies; the results have been shown to reproduce known transport data and can be readily applied to predict unknown transport properties for like-atom interactions.
NASA Astrophysics Data System (ADS)
Kumar, D. Sanjeev; Boda, Aalu; Mukhopadhyay, Soma; Chatterjee, Ashok
2015-12-01
The ground state energy of a neutral hydrogenic donor impurity (D0) trapped in a three-dimensional GaAs quantum dot with Gaussian confinement is calculated in the presence of Rashba spin-orbit interaction. The effect of the spin-orbit interaction is incorporated by performing a unitary transformation and retaining terms up to quadratic in the spin-orbit interaction coefficient. For the resulting Hamiltonian, the Rayleigh-Ritz variational method is employed with a simple wave function within the framework of effective-mass envelope function theory to determine the ground state energy and the binding energy of the donor complex. The results show that the Rashba spin-orbit interaction reduces the total GS energy of the donor impurity.
Guerout, R.; Aymar, M.; Dulieu, O.
2010-10-15
In this study, we investigate the structure of the polar alkali-metal-atom-strontium diatomic molecules as possible candidates for the realization of samples of ultracold polar molecular species not yet investigated experimentally. Using a quantum chemistry approach based on effective core potentials and core polarization potentials, we model these systems as effective three-valence-electron systems, allowing for calculation of electronic properties with full configuration interaction. The potential curve and the permanent dipole moment of the {sup 2}{Sigma}{sup +} ground state are determined as functions of the internuclear distance for LiSr, NaSr, KSr, RbSr, and CsSr molecules. These molecules are found to exhibit a significant permanent dipole moment, though smaller than those of the alkali-metal-atom-Rb molecules.
NASA Astrophysics Data System (ADS)
Iordanov, Tzvetelin D.; Davis, Jesse L.; Masunov, Artëm E.; Levenson, Andrew; Przhonska, Olga V.; Kachkovski, Alexei D.
Charge localization and dynamics in conjugated organic molecules, as well as their spectral signatures are of great importance for photonic and photovoltaic applications. Intramolecular charge delocalization in polymethine dyes occurs through π-conjugated bridges and contributes to the appearance of low-energy excited states that strongly influence their linear and nonlinear optical (NLO) properties. When the chain length in symmetrical cations exceeds the characteristic size of the soliton, the positive charge may localize at one of the terminal groups of the molecule and induce symmetry breaking of both the electron density distribution and molecular geometry. This charge localization is coupled with molecular vibrations and solvent effects. We investigated the mechanism of symmetry breaking in a series of cationic streptocyanines with different conjugated chain length and qualitatively predicted their electronic absorption spectra. This class of organic molecules is chosen as a model system to develop methodology which can subsequently be used to evaluate more complicated compounds for NLO applications. Our calculations show that the minimum number of vinylene groups in the conjugated chain necessary to break the symmetry of streptocyanines is eight in the gas phase and six in cyclohexane. We constructed the ground state potential energy surface (PES) in two dimensions using symmetry breaking and symmetry adapted coordinates. These were defined as the difference and the sum of the two central carbon-carbon bonds, respectively. This PES was found to have two equivalent minima for systems with symmetry breaking. The energy barrier between these two minima was estimated in the gas phase and in solution, which was taken into account by the polarizable continuum model. Charge localization in each minimum was found to be asymmetric. It is additionally stabilized by the solvent reaction field, which increases the energy barrier. The electronic absorption spectrum in
Transport properties of ground state oxygen atoms
NASA Technical Reports Server (NTRS)
Holland, Paul M.; Biolsi, Louis
1988-01-01
The transport properties of dilute monatomic gases depend on the two-body interactions between like atoms. When two ground-state oxygen atoms interact, they can follow any of 18 potential energy curves corresponding to O2, all of which contribute to the transport properties of the ground-state atoms. Transport collision integrals have been calculated for those interactions with an attractive minimum in the potential, and repulsive ab initio potential-energy curves have been accurately represented. Results are given for viscosity, thermal conductivity, and diffusion and they are compared with previous theoretical calculations.
Ground-state properties of strontium isotopes
Baran, A.; Hoehenberger, W.
1995-10-01
We present systematic constrained Hartree-Fock calculations of ground-state properties of even strontium isotopes ({ital A}=76--100) with the Skyrme interaction. Approximate projection of angular momentum is done after variation by explicit inclusion of the rotational energy {minus}{l_angle}{ital {cflx j}}{sup 2}{sub {ital x}}{r_angle}/J. This procedure allows for the determination of the ground-state deformations as well as the low rotational states. The binding energies, rms radii, quadrupole moments, and rotational states are discussed.
Li, Y. Q.; Zhang, P. Y.; Han, K. L.
2015-03-28
A global many-body expansion potential energy surface is reported for the electronic ground state of CH{sub 2}{sup +} by fitting high level ab initio energies calculated at the multireference configuration interaction level with the aug-cc-pV6Z basis set. The topographical features of the new global potential energy surface are examined in detail and found to be in good agreement with those calculated directly from the raw ab initio energies, as well as previous calculations available in the literature. In turn, in order to validate the potential energy surface, a test theoretical study of the reaction CH{sup +}(X{sup 1}Σ{sup +})+H({sup 2}S)→C{sup +}({sup 2}P)+H{sub 2}(X{sup 1}Σ{sub g}{sup +}) has been carried out with the method of time dependent wavepacket on the title potential energy surface. The total integral cross sections and the rate coefficients have been calculated; the results determined that the new potential energy surface can both be recommended for dynamics studies of any type and as building blocks for constructing the potential energy surfaces of larger C{sup +}/H containing systems.
Morozov, S. V.; Kryzhkov, D. I. Aleshkin, V. Ya.; Yablonsky, A. N.; Krasilnik, Z. F.; Zvonkov, B. N.; Vikhrova, O. V.
2014-01-13
In this work, we report on the time-resolved photoluminescence studies of a double quantum well In{sub 0.2}Ga{sub 0.8}As/GaAs{sub 0.8}Sb{sub 0.2}/GaAs heterostructure which, in contrast to the GaAsSb/GaAs structures, is expected to provide effective confinement of electrons due to additional InGaAs layer. The studies at 4.2 K have revealed a complicated nonmonotonic dependence of the ground-state transition energy on the concentration of nonequilibrium charge carriers in the quantum well. The effect observed in this work is important in terms of creating sources of radiation, including stimulated emission, on the basis of InGaAs/GaAsSb/GaAs structures.
NASA Astrophysics Data System (ADS)
Farasat, M.; Shojaei, S. H. R.; Morini, F.; Golzan, M. M.; Deleuze, M. S.
2016-04-01
The electronic structure, electron binding energy spectrum and (e, 2e) momentum distributions of aniline have been theoretically predicted at an electron impact energy of 1.500 keV on the basis of Born-Oppenheimer molecular dynamical simulations, in order to account for thermally induced nuclear motions in the initial electronic ground state. Most computed momentum profiles are rather insensitive to thermally induced alterations of the molecular structure, with the exception of the profiles corresponding to two ionization bands at electron binding energies comprised between ˜10.0 and ˜12.0 eV (band C) and between ˜16.5 and ˜20.0 eV (band G). These profiles are found to be strongly influenced by nuclear dynamics in the electronic ground state, especially in the low momentum region. The obtained results show that thermal averaging smears out most generally the spectral fingerprints that are induced by nitrogen inversion.
NASA Technical Reports Server (NTRS)
Fang, Z.; Kwong, Victor H. S.
1997-01-01
The charge transfer rate coefficient for the reaction N(2+)(2p(sup 2)P(sup 0)) + He yields products is measured by recording the time dependence of the N(2+) ions stored in an ion trap. A cylindrical radio-frequency ion trap was used to store N(2+) ions produced by laser ablation of a solid titanium nitride target. The decay of the ion signals was analyzed by single exponential least-squares fits to the data. The measured rate coefficient is 8.67(0.76) x 10(exp -11)sq cm/s. The N(2+) ions were at a mean energy of 2.7 eV while He gas was at room temperature, corresponding to an equivalent temperature of 3.9 x 10(exp 3) K. The measured value is in good agreement with a recent calculation.
Zhang, Chunfang; Fu, Mingkai; Shen, Zhitao; Ma, Haitao; Bian, Wensheng
2014-06-21
A new global ab initio potential energy surface (called ZMB-a) for the 1(1)A' state of the C((1)D)+H2 reactive system has been constructed. This is based upon ab initio calculations using the internally contracted multireference configuration interaction approach with the aug-cc-pVQZ basis set, performed at about 6300 symmetry unique geometries. Accurate analytical fits are generated using many-body expansions with the permutationally invariant polynomials, except that the fit of the deep well region is taken from our previous fit. The ZMB-a surface is unique in the accurate description of the regions around conical intersections (CIs) and of van der Waals (vdW) interactions. The CIs between the 1(1)A' and 2(1)A' states cause two kinds of barriers on the ZMB-a surface: one is in the linear H-CH dissociation direction with a barrier height of 9.07 kcal/mol, which is much higher than those on the surfaces reported before; the other is in the C((1)D) collinearly attacking H2 direction with a barrier height of 12.39 kcal/mol. The ZMB-a surface basically reproduces our ab initio calculations in the vdW interaction regions, and supports a linear C-HH vdW complex in the entrance channel, and two vdW complexes in the exit channel, at linear CH-H and HC-H geometries, respectively.
Pejlovas, Aaron M; Lin, Wei; Kukolich, Stephen G
2015-10-01
Microwave spectra for a higher-energy conformer of cyclopropanecarboxylic acid (CPCA) were measured using a Flygare-Balle-type pulsed-beam Fourier transform microwave spectrometer. The rotational constants (in megahertz) and centrifugal distortion constants (in kilohertz) for this higher-energy conformer are A = 7452.3132(57), B = 2789.8602(43), C = 2415.0725(40), DJ = 0.29(53), and DJK = 2.5(12). Differences between rotational constants for this excited-state conformation and the ground state are primarily due to the acidic OH bond moving from a position cis relative to the cyclopropyl group about the C1-C9 bond to the more stable trans conformation. Calculations indicate that the relative abundance of the higher-energy state should be 15% to 17% at room temperature, but the observed relative abundance for the supersonic expansion conditions is about 1%. The measurements of rotational transitions for the trans form of CPCA were extended to include all of the unique (13)C singly substituted positions. These measurements, along with previously measured transitions of the parent and -OD isotopologues, were used to determine a best-fit gas-phase structure.
NASA Astrophysics Data System (ADS)
Dixit, Anant; Ángyán, János G.; Rocca, Dario
2016-09-01
A new formalism was recently proposed to improve random phase approximation (RPA) correlation energies by including approximate exchange effects [B. Mussard et al., J. Chem. Theory Comput. 12, 2191 (2016)]. Within this framework, by keeping only the electron-hole contributions to the exchange kernel, two approximations can be obtained: An adiabatic connection analog of the second order screened exchange (AC-SOSEX) and an approximate electron-hole time-dependent Hartree-Fock (eh-TDHF). Here we show how this formalism is suitable for an efficient implementation within the plane-wave basis set. The response functions involved in the AC-SOSEX and eh-TDHF equations can indeed be compactly represented by an auxiliary basis set obtained from the diagonalization of an approximate dielectric matrix. Additionally, the explicit calculation of unoccupied states can be avoided by using density functional perturbation theory techniques and the matrix elements of dynamical response functions can be efficiently computed by applying the Lanczos algorithm. As shown by several applications to reaction energies and weakly bound dimers, the inclusion of the electron-hole kernel significantly improves the accuracy of ground-state correlation energies with respect to RPA and semi-local functionals.
Dixit, Anant; Ángyán, János G; Rocca, Dario
2016-09-14
A new formalism was recently proposed to improve random phase approximation (RPA) correlation energies by including approximate exchange effects [B. Mussard et al., J. Chem. Theory Comput. 12, 2191 (2016)]. Within this framework, by keeping only the electron-hole contributions to the exchange kernel, two approximations can be obtained: An adiabatic connection analog of the second order screened exchange (AC-SOSEX) and an approximate electron-hole time-dependent Hartree-Fock (eh-TDHF). Here we show how this formalism is suitable for an efficient implementation within the plane-wave basis set. The response functions involved in the AC-SOSEX and eh-TDHF equations can indeed be compactly represented by an auxiliary basis set obtained from the diagonalization of an approximate dielectric matrix. Additionally, the explicit calculation of unoccupied states can be avoided by using density functional perturbation theory techniques and the matrix elements of dynamical response functions can be efficiently computed by applying the Lanczos algorithm. As shown by several applications to reaction energies and weakly bound dimers, the inclusion of the electron-hole kernel significantly improves the accuracy of ground-state correlation energies with respect to RPA and semi-local functionals. PMID:27634249
Zhang, Chunfang; Fu, Mingkai; Shen, Zhitao; Ma, Haitao; Bian, Wensheng
2014-06-21
A new global ab initio potential energy surface (called ZMB-a) for the 1(1)A' state of the C((1)D)+H2 reactive system has been constructed. This is based upon ab initio calculations using the internally contracted multireference configuration interaction approach with the aug-cc-pVQZ basis set, performed at about 6300 symmetry unique geometries. Accurate analytical fits are generated using many-body expansions with the permutationally invariant polynomials, except that the fit of the deep well region is taken from our previous fit. The ZMB-a surface is unique in the accurate description of the regions around conical intersections (CIs) and of van der Waals (vdW) interactions. The CIs between the 1(1)A' and 2(1)A' states cause two kinds of barriers on the ZMB-a surface: one is in the linear H-CH dissociation direction with a barrier height of 9.07 kcal/mol, which is much higher than those on the surfaces reported before; the other is in the C((1)D) collinearly attacking H2 direction with a barrier height of 12.39 kcal/mol. The ZMB-a surface basically reproduces our ab initio calculations in the vdW interaction regions, and supports a linear C-HH vdW complex in the entrance channel, and two vdW complexes in the exit channel, at linear CH-H and HC-H geometries, respectively. PMID:24952535
NASA Astrophysics Data System (ADS)
dos Santos, A. V.; Samudio Pérez, C. A.; Muenchen, D.; Anibele, T. P.
2015-01-01
-O multilayers. Firstly, the formation energy and the cohesive energy of the multilayers are discussed. For optimised values, the cohesive energy of the multilayers to obtain the lattice parameters at the equilibrium ground state was used, i.e. a new methodology for this calculus was applied. Secondly, the magnetic properties and hyperfine interactions (magnetic field, electric field gradient and the isomer shift) of the iron atoms of the multilayers are discussed.
Gou, Dezhi; Kuang, Xiaoyu Gao, Yufeng; Huo, Dongming
2015-01-21
In this paper, we systematically investigate the electronic structure for the {sup 2}Σ{sup +} ground state of the polar alkali-metal-alkaline-earth-metal molecules BaAlk (Alk = Li, Na, K, Rb, and Cs). Potential energy curves and permanent dipole moments (PDMs) are determined using power quantum chemistry complete active space self-consistent field and multi-reference configuration interaction methods. Basic spectroscopic constants are derived from ro-vibrational bound state calculation. From the calculations, it is shown that BaK, BaRb, and BaCs molecules have moderate values of PDM at the equilibrium bond distance (BaK:1.62 D, BaRb:3.32 D, and BaCs:4.02 D). Besides, the equilibrium bond length (4.93 Å and 5.19 Å) and dissociation energy (0.1825 eV and 0.1817 eV) for the BaRb and BaCs are also obtained.
Munteanu, Cristian Robert; Fernández, Berta
2005-07-01
Accurate ground-state intermolecular potential-energy surfaces are obtained for the HCCH-He, Ne, and Ar van der Waals complexes. The interaction energies are calculated at the coupled cluster singles and doubles including connected triple excitations level and fitted to analytic functions. For the three complexes we start with systematic basis set studies carried out at several intermolecular geometries, and using augmented correlation consistent polarized valence basis sets x-aug-cc-pVXZ (x=-,d; X=D,T,Q,5), also extended with a set of 3s3p2d1f1g midbond functions. The aug-cc-pVQZ-33211 surfaces of HCCH-He, Ne, and Ar complexes are characterized by absolute minima of -24.22, -50.20, and -122.17 cm(-1) at distances R between the rare-gas atom and the HCCH centers of mass of 4.35, 3.95, and 3.99 A, respectively; and at angles between the vector R and the HCCH main symmetry axis of 0 degrees , 43.3 degrees , and 60.6 degrees . The results are compared and considerably improve those previously available.
NASA Astrophysics Data System (ADS)
Gou, Dezhi; Kuang, Xiaoyu; Gao, Yufeng; Huo, Dongming
2015-01-01
In this paper, we systematically investigate the electronic structure for the 2Σ+ ground state of the polar alkali-metal-alkaline-earth-metal molecules BaAlk (Alk = Li, Na, K, Rb, and Cs). Potential energy curves and permanent dipole moments (PDMs) are determined using power quantum chemistry complete active space self-consistent field and multi-reference configuration interaction methods. Basic spectroscopic constants are derived from ro-vibrational bound state calculation. From the calculations, it is shown that BaK, BaRb, and BaCs molecules have moderate values of PDM at the equilibrium bond distance (BaK:1.62 D, BaRb:3.32 D, and BaCs:4.02 D). Besides, the equilibrium bond length (4.93 Å and 5.19 Å) and dissociation energy (0.1825 eV and 0.1817 eV) for the BaRb and BaCs are also obtained.
Ground states of holographic superconductors
Gubser, Steven S.; Nellore, Abhinav
2009-11-15
We investigate the ground states of the Abelian Higgs model in AdS{sub 4} with various choices of parameters, and with no deformations in the ultraviolet other than a chemical potential for the electric charge under the Abelian gauge field. For W-shaped potentials with symmetry-breaking minima, an analysis of infrared asymptotics suggests that the ground state has emergent conformal symmetry in the infrared when the charge of the complex scalar is large enough. But when this charge is too small, the likeliest ground state has Lifshitz-like scaling in the infrared. For positive mass quadratic potentials, Lifshitz-like scaling is the only possible infrared behavior for constant nonzero values of the scalar. The approach to Lifshitz-like scaling is shown in many cases to be oscillatory.
Wang, Yimin; Braams, Bastiaan J; Bowman, Joel M; Carter, Stuart; Tew, David P
2008-06-14
Quantum calculations of the ground vibrational state tunneling splitting of H-atom and D-atom transfer in malonaldehyde are performed on a full-dimensional ab initio potential energy surface (PES). The PES is a fit to 11 147 near basis-set-limit frozen-core CCSD(T) electronic energies. This surface properly describes the invariance of the potential with respect to all permutations of identical atoms. The saddle-point barrier for the H-atom transfer on the PES is 4.1 kcalmol, in excellent agreement with the reported ab initio value. Model one-dimensional and "exact" full-dimensional calculations of the splitting for H- and D-atom transfer are done using this PES. The tunneling splittings in full dimensionality are calculated using the unbiased "fixed-node" diffusion Monte Carlo (DMC) method in Cartesian and saddle-point normal coordinates. The ground-state tunneling splitting is found to be 21.6 cm(-1) in Cartesian coordinates and 22.6 cm(-1) in normal coordinates, with an uncertainty of 2-3 cm(-1). This splitting is also calculated based on a model which makes use of the exact single-well zero-point energy (ZPE) obtained with the MULTIMODE code and DMC ZPE and this calculation gives a tunneling splitting of 21-22 cm(-1). The corresponding computed splittings for the D-atom transfer are 3.0, 3.1, and 2-3 cm(-1). These calculated tunneling splittings agree with each other to within less than the standard uncertainties obtained with the DMC method used, which are between 2 and 3 cm(-1), and agree well with the experimental values of 21.6 and 2.9 cm(-1) for the H and D transfer, respectively.
Cybulski, Hubert; Baranowska-Łączkowska, Angelika; Henriksen, Christian; Fernández, Berta
2014-11-01
By evaluating a representative set of CCSD(T) ground state interaction energies for van der Waals dimers formed by aromatic molecules and the argon atom, we test the performance of the polarized basis sets of Sadlej et al. (J. Comput. Chem. 2005, 26, 145; Collect. Czech. Chem. Commun. 1988, 53, 1995) and the augmented polarization-consistent bases of Jensen (J. Chem. Phys. 2002, 117, 9234) in providing accurate intermolecular potentials for the benzene-, naphthalene-, and anthracene-argon complexes. The basis sets are extended by addition of midbond functions. As reference we consider CCSD(T) results obtained with Dunning's bases. For the benzene complex a systematic basis set study resulted in the selection of the (Z)Pol-33211 and the aug-pc-1-33321 bases to obtain the intermolecular potential energy surface. The interaction energy values and the shape of the CCSD(T)/(Z)Pol-33211 calculated potential are very close to the best available CCSD(T)/aug-cc-pVTZ-33211 potential with the former basis set being considerably smaller. The corresponding differences for the CCSD(T)/aug-pc-1-33321 potential are larger. In the case of the naphthalene-argon complex, following a similar study, we selected the (Z)Pol-3322 and aug-pc-1-333221 bases. The potentials show four symmetric absolute minima with energies of -483.2 cm(-1) for the (Z)Pol-3322 and -486.7 cm(-1) for the aug-pc-1-333221 basis set. To further check the performance of the selected basis sets, we evaluate intermolecular bound states of the complexes. The differences between calculated vibrational levels using the CCSD(T)/(Z)Pol-33211 and CCSD(T)/aug-cc-pVTZ-33211 benzene-argon potentials are small and for the lowest energy levels do not exceed 0.70 cm(-1). Such differences are substantially larger for the CCSD(T)/aug-pc-1-33321 calculated potential. For naphthalene-argon, bound state calculations demonstrate that the (Z)Pol-3322 and aug-pc-1-333221 potentials are of similar quality. The results show that these
Ground State Studies of Spin Glass Models.
NASA Astrophysics Data System (ADS)
Kolan, Amy Joanne
The ground state energy and degeneracy for a set of spin glass models, PQR models, has been studied in detail. For the pure frustration case, a subset of the general PQR case, we have studied the spacial distribution of frustrated plaquettes at T = 0. We investigated the "frustration -frustration" correlation function, which involved a series expansion analysis and a computer analysis, to examine a phase transition mechanism proposed by Schuster (1981). Schuster suggested that a pair of plaquettes is bound together above, and dissociated below a critical concentration of antiferromagnetic bonds. Our analysis, however, led us to conclude that there is no sharp "unbinding" of frustration pairs. We have developed an efficient algorithm to compute the ground state energy and degeneracy of sample PQR lattices and have studied the general PQR model numerically. Our algorithm is similar in essence to Morgenstern and Binder's (1980) transfer matrix approach used to calculate the partition function of a sample of spins in the pure frustration case. The algorithm involves computing times of order ALM 2('L), where L is the width of the lattice, M is the length, and A is a constant of proportionality. We have used the results of our analysis to investigate the possibility of a paramagnetic (<--->) spin glass phase transition in the PQR model at T = 0. Although scatter in our results for the ground state degeneracy/spin obscures evidence of a possible non-analyticity in this function, we do see evidence of a "break" in the curves for the ground state energy/spin. We have used this "break" to plot the phase transition line between the spin glass and paramagnetic regimes.
Moving Toward the Ground State.
Kumar, Ishan; Ivanova, Natalia
2015-10-01
Transferring mouse ESCs to a media supplemented with Mek and Gsk3β inhibitors (2i) provokes marked transcriptional and epigenetic changes, embodying a shift toward ground-state pluripotency. In this issue of Cell Stem Cell, Kolodziejczyk et al. (2015) examine population structures of ESCs while Galonska et al. (2015) unravel the mechanisms underlying regulatory network rewiring during 2i-mediated reprogramming. PMID:26431178
Ground state searches in fcc intermetallics
Wolverton, C.; de Fontaine, D. ); Ceder, G. ); Dreysse, H. . Lab. de Physique du Solide)
1991-12-01
A cluster expansion is used to predict the fcc ground states, i.e., the stable phases at zero Kelvin as a function of composition, for alloy systems. The intermetallic structures are not assumed, but derived regorously by minimizing the configurational energy subject to linear constraints. This ground state search includes pair and multiplet interactions which spatially extend to fourth nearest neighbor. A large number of these concentration-independent interactions are computed by the method of direct configurational averaging using a linearized-muffin-tin orbital Hamiltonian cast into tight binding form (TB-LMTO). The interactions, derived without the use of any adjustable or experimentally obtained parameters, are compared to those calculated via the generalized perturbation method extention of the coherent potential approximation within the context of a KKR Hamiltonian (KKR-CPA-GPM). Agreement with the KKR-CPA-GPM results is quite excellent, as is the comparison of the ground state results with the fcc-based portions of the experimentally-determined phase diagrams under consideration.
Two different ground states in K-intercalated polyacenes
NASA Astrophysics Data System (ADS)
Phan, Quynh T. N.; Heguri, Satoshi; Tamura, Hiroyuki; Nakano, Takehito; Nozue, Yasuo; Tanigaki, Katsumi
2016-02-01
The electronic states of potassium- (K-) intercalated zigzag-type polycyclic aromatic (PLA) hydrocarbon [polyacene PLAs] Kx(PLAs ) are studied for a series of the four smallest molecules: naphthalene (NN), anthracene (AN), tetracene (TN), and pentacene (PN), focusing on their 1:1 stoichiometric phases. Clear experimental differences are identified between the first group [K1(NN ) and K1(AN ) ] and the second group [K1(TN ) and K1(PN ) ] by magnetic, vibrational, and optical measurements. The first group is categorized as a Mott insulator with an antiferromagnetic ground state with energy of ˜10 meV, whereas the second group is classified as a band insulator via dimer formation due to the spin Peierls instability. In the latter system, the first thermally accessible triplet states are located far apart from the singlet ground states and are not detected by electron spin-resonance spectroscopy until 300 K being very different from what is observed for the hole-doped PN reported earlier. The results give a new systematic understanding on the electronic states of electron-doped PLAs sensitive to the energetic balance among on-site Coulomb repulsion, bandwidth, and the Peierls instability.
Phase diagram of the ground states of DNA condensates
NASA Astrophysics Data System (ADS)
Hoang, Trinh X.; Trinh, Hoa Lan; Giacometti, Achille; Podgornik, Rudolf; Banavar, Jayanth R.; Maritan, Amos
2015-12-01
The phase diagram of the ground states of DNA in a bad solvent is studied for a semiflexible polymer model with a generalized local elastic bending potential characterized by a nonlinearity parameter x and effective self-attraction promoting compaction. x =1 corresponds to the wormlike chain model. Surprisingly, the phase diagram as well as the transition lines between the ground states are found to be a function of x . The model provides a simple explanation for the results of prior experimental and computational studies and makes predictions for the specific geometries of the ground states. The results underscore the impact of the form of the microscopic bending energy at macroscopic observable scales.
Ground states of stealthy hyperuniform potentials: I. Entropically favored configurations
NASA Astrophysics Data System (ADS)
Zhang, G.; Stillinger, F. H.; Torquato, S.
2015-08-01
Systems of particles interacting with "stealthy" pair potentials have been shown to possess infinitely degenerate disordered hyperuniform classical ground states with novel physical properties. Previous attempts to sample the infinitely degenerate ground states used energy minimization techniques, introducing algorithmic dependence that is artificial in nature. Recently, an ensemble theory of stealthy hyperuniform ground states was formulated to predict the structure and thermodynamics that was shown to be in excellent agreement with corresponding computer simulation results in the canonical ensemble (in the zero-temperature limit). In this paper, we provide details and justifications of the simulation procedure, which involves performing molecular dynamics simulations at sufficiently low temperatures and minimizing the energy of the snapshots for both the high-density disordered regime, where the theory applies, as well as lower densities. We also use numerical simulations to extend our study to the lower-density regime. We report results for the pair correlation functions, structure factors, and Voronoi cell statistics. In the high-density regime, we verify the theoretical ansatz that stealthy disordered ground states behave like "pseudo" disordered equilibrium hard-sphere systems in Fourier space. The pair statistics obey certain exact integral conditions with very high accuracy. These results show that as the density decreases from the high-density limit, the disordered ground states in the canonical ensemble are characterized by an increasing degree of short-range order and eventually the system undergoes a phase transition to crystalline ground states. In the crystalline regime (low densities), there exist aperiodic structures that are part of the ground-state manifold but yet are not entropically favored. We also provide numerical evidence suggesting that different forms of stealthy pair potentials produce the same ground-state ensemble in the zero
Ground state fidelity from tensor network representations.
Zhou, Huan-Qiang; Orús, Roman; Vidal, Guifre
2008-02-29
For any D-dimensional quantum lattice system, the fidelity between two ground state many-body wave functions is mapped onto the partition function of a D-dimensional classical statistical vertex lattice model with the same lattice geometry. The fidelity per lattice site, analogous to the free energy per site, is well defined in the thermodynamic limit and can be used to characterize the phase diagram of the model. We explain how to compute the fidelity per site in the context of tensor network algorithms, and demonstrate the approach by analyzing the two-dimensional quantum Ising model with transverse and parallel magnetic fields. PMID:18352611
Best Possible Strategy for Finding Ground States
NASA Astrophysics Data System (ADS)
Franz, Astrid; Hoffmann, Karl Heinz; Salamon, Peter
2001-06-01
Finding the ground state of a system with a complex energy landscape is important for many physical problems including protein folding, spin glasses, chemical clusters, and neural networks. Such problems are usually solved by heuristic search methods whose efficacy is judged by empirical performance on selected examples. We present a proof that, within the large class of algorithms that simulate a random walk on the landscape, threshold accepting is the best possible strategy. In particular, it can perform better than simulated annealing and Tsallis statistics. Our proof is the first example of a provably optimal strategy in this area.
Exact ground states of disordered systems
NASA Astrophysics Data System (ADS)
Mienke, Jan Hermann
Finding the ground state of disordered systems is in general a hard problem. Mappings of disordered systems to problems from computer science for which efficient, i.e., polynomial algorithms are known allow the numerical study of large systems. I study the ground state of the random-field Ising model both analytically using mean field approximations and numerically in 3D. I find that the behavior for the infinite-range model is nonuniversal in the sense that the critical exponent beta can vary continuously. On the Cayley tree, however, the behavior is universal. I develop a theory for the roughening of the minimum energy fracture surface in polycrystalline materials as a function of the relevant energy parameter epsilon = epsiloni/epsilon g. epsilong is the internal binding energy of the grain and epsiloni is the adhesion energy. Both local and global effects contribute to the roughening and have to be taken into account. This leads to an epsilon-dependent critical length Lc. For systems with L > L c and epsilon < 1 the interface is always rough.
NASA Astrophysics Data System (ADS)
Ishikawa, Haruki; Nakano, Takumi; Takashima, Tsukiko; Yabuguchi, Hiroki; Fuke, Kiyokazu
2013-06-01
In order to investigate the deuteration effect on the vibrational dynamics of the NH and/or ND stretch excited levels of the 7-azaindole (7-AI) normal dimer and its tautomeric dimer, we have carried out infrared spectroscopy of three isotopic species for each dimers; undeuterated one (NH-NH) and one or two hydrogen atom(s) of the NH groups is deuterated ones (NH-ND and ND-ND, respectively). It is found that the ND stretch band profiles of the NH-ND and ND-ND tautomeric dimers are very similar with each other. This result is very distinct from the result of the comparison of the NH stretch band profiles of the NH-NH and NH-ND dimers in our previous study. For a further discussion, we have examined the deuteration effect in the case of the 7-AI normal dimer. It is found that the NH stretch band profiles of the NH-NH and the NH-ND dimers and also the ND stretch band profiles of the NH-ND and the ND-ND dimers exhibit similar patterns, respectively. These facts indicates that the vibrational relaxation from the NH/ND stretch level of the normal dimer basically proceed within a monomer unit. The large deuteration effect of the NH stretch band profile observed previously is found to be characteristic of the tautomeric dimer. This behavior is related to a large anharmonicity of the potential energy surface originating from an existence of the double-proton transfer reaction barrier. H. Ishikawa, H. Yabuguchi, Y. Yamada, A. Fujihara, K. Fuke, J. Phys. Chem. A 114, 3199 (2010).
Electronic Structure and Ground State Properties of Non-Magnetic NiPt Systems
NASA Astrophysics Data System (ADS)
PAUDYAL, DURGA; MOOKERJEE, ABHIJIT
We have studied the electronic properties like density of states and band structures and also the ground state properties like formation energy, cohesive energy, bulk modulus and structural energy of NiPt system using the linearized muffin-tin orbital method introduced by Andersen.1,2 In an earlier communication we had argued that both charge neutrality and scalar relativistic corrections are very important for the high concentration of Pt alloys. The calculations here, were, therefore, carried out with charge neutrality as well as with and without scalar relativistic correction for comparison.
Ferromagnetic Ground States in Face-Centered Cubic Hubbard Clusters
Souza, T. X. R.; Macedo, C. A.
2016-01-01
In this study, the ground state energies of face-centered cubic Hubbard clusters are analyzed using the Lanczos method. Examination of the ground state energy as a function of the number of particle per site n showed an energy minimum for face-centered cubic structures. This energy minimum decreased in n with increasing coulombic interaction parameter U. We found that the ground state energy had a minimum at n = 0.6, when U = 3W, where W denotes the non-interacting energy bandwidth and the face-centered cubic structure was ferromagnetic. These results, when compared with the properties of nickel, shows strong similarity with other finite temperature analyses in the literature and supports the Hirsh’s conjecture that the interatomic direct exchange interaction dominates in driving the system into a ferromagnetic phase. PMID:27583653
Ferromagnetic Ground States in Face-Centered Cubic Hubbard Clusters.
Souza, T X R; Macedo, C A
2016-01-01
In this study, the ground state energies of face-centered cubic Hubbard clusters are analyzed using the Lanczos method. Examination of the ground state energy as a function of the number of particle per site n showed an energy minimum for face-centered cubic structures. This energy minimum decreased in n with increasing coulombic interaction parameter U. We found that the ground state energy had a minimum at n = 0.6, when U = 3W, where W denotes the non-interacting energy bandwidth and the face-centered cubic structure was ferromagnetic. These results, when compared with the properties of nickel, shows strong similarity with other finite temperature analyses in the literature and supports the Hirsh's conjecture that the interatomic direct exchange interaction dominates in driving the system into a ferromagnetic phase. PMID:27583653
Ground-state structures of Hafnium clusters
Ng, Wei Chun; Yoon, Tiem Leong; Lim, Thong Leng
2015-04-24
Hafnium (Hf) is a very large tetra-valence d-block element which is able to form relatively long covalent bond. Researchers are interested to search for substitution to silicon in the semi-conductor industry. We attempt to obtain the ground-state structures of small Hf clusters at both empirical and density-functional theory (DFT) levels. For calculations at the empirical level, charge-optimized many-body functional potential (COMB) is used. The lowest-energy structures are obtained via a novel global-minimum search algorithm known as parallel tempering Monte-Carlo Basin-Hopping and Genetic Algorithm (PTMBHGA). The virtue of using COMB potential for Hf cluster calculation lies in the fact that by including the charge optimization at the valence shells, we can encourage the formation of proper bond hybridization, and thus getting the correct bond order. The obtained structures are further optimized using DFT to ensure a close proximity to the ground-state.
Ground state of a hydrogen ion molecule immersed in an inhomogeneous electron gas
NASA Astrophysics Data System (ADS)
Diaz-Valdes, J.; Gutierrez, F. A.; Matamala, A. R.; Denton, C. D.; Vargas, P.; Valdes, J. E.
2007-01-01
In this work we have calculated the ground state energy of the hydrogen molecule, H2+, immersed in the highly inhomogeneous electron gas around a metallic surface within the local density approximation. The molecule is perturbed by the electron density of a crystalline surface of Au <1 0 0> with the internuclear axis parallel to the surface. The surface spatial electron density is calculated through a linearized band structure method (LMTO-DFT). The ground state of the molecule-ion was calculated using the Born-Oppenheimer approximation for a fixed-ion while the screening effects of the inhomogeneous electron gas are depicted by a Thomas-Fermi like electrostatic potential. We found that within our model the molecular ion dissociates at the critical distance of 2.35 a.u. from the first atomic layer of the solid.
Density of States for Warped Energy Bands
NASA Astrophysics Data System (ADS)
Mecholsky, Nicholas A.; Resca, Lorenzo; Pegg, Ian L.; Fornari, Marco
2016-02-01
Warping of energy bands can affect the density of states (DOS) in ways that can be large or subtle. Despite their potential for significant practical impacts on materials properties, these effects have not been rigorously demonstrated previously. Here we rectify this using an angular effective mass formalism that we have developed. To clarify the often confusing terminology in this field, “band warping” is precisely defined as pertaining to any multivariate energy function E(k) that does not admit a second-order differential at an isolated critical point in k-space, which we clearly distinguish from band non-parabolicity. We further describe band “corrugation” as a qualitative form of band warping that increasingly deviates from being twice differentiable at an isolated critical point. These features affect the density-of-states and other parameters ascribed to band warping in various ways. We demonstrate these effects, providing explicit calculations of DOS and their effective masses for warped energy dispersions originally derived by Kittel and others. Other physical and mathematical examples are provided to demonstrate fundamental distinctions that must be drawn between DOS contributions that originate from band warping and contributions that derive from band non-parabolicity. For some non-degenerate bands in thermoelectric materials, this may have profound consequences of practical interest.
Density of States for Warped Energy Bands
Mecholsky, Nicholas A.; Resca, Lorenzo; Pegg, Ian L.; Fornari, Marco
2016-01-01
Warping of energy bands can affect the density of states (DOS) in ways that can be large or subtle. Despite their potential for significant practical impacts on materials properties, these effects have not been rigorously demonstrated previously. Here we rectify this using an angular effective mass formalism that we have developed. To clarify the often confusing terminology in this field, “band warping” is precisely defined as pertaining to any multivariate energy function E(k) that does not admit a second-order differential at an isolated critical point in k-space, which we clearly distinguish from band non-parabolicity. We further describe band “corrugation” as a qualitative form of band warping that increasingly deviates from being twice differentiable at an isolated critical point. These features affect the density-of-states and other parameters ascribed to band warping in various ways. We demonstrate these effects, providing explicit calculations of DOS and their effective masses for warped energy dispersions originally derived by Kittel and others. Other physical and mathematical examples are provided to demonstrate fundamental distinctions that must be drawn between DOS contributions that originate from band warping and contributions that derive from band non-parabolicity. For some non-degenerate bands in thermoelectric materials, this may have profound consequences of practical interest. PMID:26905029
Ground state of high-density matter
NASA Technical Reports Server (NTRS)
Copeland, ED; Kolb, Edward W.; Lee, Kimyeong
1988-01-01
It is shown that if an upper bound to the false vacuum energy of the electroweak Higgs potential is satisfied, the true ground state of high-density matter is not nuclear matter, or even strange-quark matter, but rather a non-topological soliton where the electroweak symmetry is exact and the fermions are massless. This possibility is examined in the standard SU(3) sub C tensor product SU(2) sub L tensor product U(1) sub Y model. The bound to the false vacuum energy is satisfied only for a narrow range of the Higgs boson masses in the minimal electroweak model (within about 10 eV of its minimum allowed value of 6.6 GeV) and a somewhat wider range for electroweak models with a non-minimal Higgs sector.
NASA Astrophysics Data System (ADS)
Mehboudi, Mehrshad; Barraza-Lopez, Salvador; Dorio, Alex M.; Zhu, Wenjuan; van der Zande, Arend; Churchill, Hugh O. H.; Pacheco-Sanjuan, Alejandro A.; Harriss, Edmund O.; Kumar, Pradeep
Mono-layers of black phosphorus and other two dimensional materials such as mono-layers of SiSe, GeS, GeSe, GeTe, Sns, SnSe, and SnTe with a similar crystalline structure have a four-fold degenerate ground state that leads to two-dimensional disorder at finite temperature. Disorder happens when neighboring atoms gently re-accommodate bonds beyond a critical temperature. In this talk, the effect of atomic numbers on the transition temperature will be discussed. In addition Car-Parinello molecular dynamics calculations at temperatures 30, 300 and 1000 K were performed on supercells containing more than five hundred atoms and the results from these calculations confirm the transition onto a two-dimensional disordered structure past the critical temperature, which is close to room temperature for many of these compounds. References: M. Mehboudi, A.M. Dorio, W. Zhu, A. van der Zande, H.O.H. Churchill, A.A. Pacheco Sanjuan, E.O.H. Harris, P. Kumar, and S. Barraza-Lopez. arXiv:1510.09153.
Efficient algorithm for approximating one-dimensional ground states
Aharonov, Dorit; Arad, Itai; Irani, Sandy
2010-07-15
The density-matrix renormalization-group method is very effective at finding ground states of one-dimensional (1D) quantum systems in practice, but it is a heuristic method, and there is no known proof for when it works. In this article we describe an efficient classical algorithm which provably finds a good approximation of the ground state of 1D systems under well-defined conditions. More precisely, our algorithm finds a matrix product state of bond dimension D whose energy approximates the minimal energy such states can achieve. The running time is exponential in D, and so the algorithm can be considered tractable even for D, which is logarithmic in the size of the chain. The result also implies trivially that the ground state of any local commuting Hamiltonian in 1D can be approximated efficiently; we improve this to an exact algorithm.
Attractive Correlated Electron-Pair Ground State of Resonant Bosons
NASA Astrophysics Data System (ADS)
Chakraverty, B. K.
We consider a strictly one-band Hamiltonian of electrons with attractive interaction between them. We show that in the interesting intermediate density regime, where V ≤ ɛF, the system admits a mixed state of free fermions and dynamic correlated pairs or resonant bosons. The inevitable coupling between the two sub-system produces a superconducting ground state. This should be called Schafroth Condensation.
Ground state microstructure of a ferrofluid thin layer
Prokopieva, T. A.; Danilov, V. A.; Kantorovich, S. S.
2011-09-15
Using a fine weave of theoretical analysis and computer simulations, we found various aggregates of magnetic single-domain nanoparticles, which can form in a quasi-two-dimensional (q2D) ferrofluid layer at low temperatures. Our theoretical investigation allowed us to obtain exact expressions and their asymptotes for the energies of each configuration. Thus, for ferrofluid q2D layers it proved possible to identify the ground states as a function of the particle number, size, and other system parameters. Our suggested approach can be used for the investigation of ground state structures in systems with more complex interparticle interactions.
Spin of the sup 219 Ra ground state
Hackett, E.D.; Kuehner, J.A.; Waddington, J.C. ); Jones, G.D.
1989-09-01
The {sup 208}Pb({sup 18}O,3{ital n}){sup 223}Th reaction at 83 MeV bombarding energy was used to populate the alpha-radioactive nucleus {sup 223}Th. Out-of-beam alpha-gamma coincidences were recorded at correlation angles of 90{degree} and 180{degree}. The {ital a}{sub 2} angular correlation coefficient was extracted for an alpha-gamma cascade to the {sup 215}Rn ground state via the 0.316 MeV excited state. This limited the assignment of the ground-state spin of {sup 219}Ra to ((7/2, 11) / 2 ){sup +}. .AE
NASA Astrophysics Data System (ADS)
Isegawa, Miho; Truhlar, Donald G.
2013-04-01
Time-dependent density functional theory (TDDFT) holds great promise for studying photochemistry because of its affordable cost for large systems and for repeated calculations as required for direct dynamics. The chief obstacle is uncertain accuracy. There have been many validation studies, but there are also many formulations, and there have been few studies where several formulations were applied systematically to the same problems. Another issue, when TDDFT is applied with only a single exchange-correlation functional, is that errors in the functional may mask successes or failures of the formulation. Here, to try to sort out some of the issues, we apply eight formulations of adiabatic TDDFT to the first valence excitations of ten molecules with 18 density functionals of diverse types. The formulations examined are linear response from the ground state (LR-TDDFT), linear response from the ground state with the Tamm-Dancoff approximation (TDDFT-TDA), the original collinear spin-flip approximation with the Tamm-Dancoff (TD) approximation (SF1-TDDFT-TDA), the original noncollinear spin-flip approximation with the TDA approximation (SF1-NC-TDDFT-TDA), combined self-consistent-field (SCF) and collinear spin-flip calculations in the original spin-projected form (SF2-TDDFT-TDA) or non-spin-projected (NSF2-TDDFT-TDA), and combined SCF and noncollinear spin-flip calculations (SF2-NC-TDDFT-TDA and NSF2-NC-TDDFT-TDA). Comparing LR-TDDFT to TDDFT-TDA, we observed that the excitation energy is raised by the TDA; this brings the excitation energies underestimated by full linear response closer to experiment, but sometimes it makes the results worse. For ethylene and butadiene, the excitation energies are underestimated by LR-TDDFT, and the error becomes smaller making the TDA. Neither SF1-TDDFT-TDA nor SF2-TDDFT-TDA provides a lower mean unsigned error than LR-TDDFT or TDDFT-TDA. The comparison between collinear and noncollinear kernels shows that the noncollinear kernel
Triplet (S = 1) Ground State Aminyl Diradical
Rajca, Andrzej; Shiraishi, Kouichi; Pink, Maren; Rajca, Suchada
2008-04-02
Aminyl diradical, which is stable in solution at low temperatures, is prepared. EPR spectra and SQUID magnetometry indicate that the diradical is planar and it possesses triplet ground state, with strong ferromagnetic coupling.
Eastern Band of Cherokee Strategic Energy Plan
Souther Carolina Institute of energy Studies-Robert Leitner
2009-01-30
The Eastern Band of Cherokee Indians was awarded a grant under the U.S. Department of Energy Tribal Energy Program (TEP) to develop a Tribal Strategic Energy Plan (SEP). The grant, awarded under the “First Steps” phase of the TEP, supported the development of a SEP that integrates with the Tribe’s plans for economic development, preservation of natural resources and the environment, and perpetuation of Tribal heritage and culture. The Tribe formed an Energy Committee consisting of members from various departments within the Tribal government. This committee, together with its consultant, the South Carolina Institute for Energy Studies, performed the following activities: • Develop the Tribe’s energy goals and objectives • Establish the Tribe’s current energy usage • Identify available renewable energy and energy efficiency options • Assess the available options versus the goals and objectives • Create an action plan for the selected options
Ensemble Theory for Stealthy Hyperuniform Disordered Ground States
NASA Astrophysics Data System (ADS)
Torquato, S.; Zhang, G.; Stillinger, F. H.
2015-04-01
It has been shown numerically that systems of particles interacting with isotropic "stealthy" bounded long-ranged pair potentials (similar to Friedel oscillations) have classical ground states that are (counterintuitively) disordered, hyperuniform, and highly degenerate. Disordered hyperuniform systems have received attention recently because they are distinguishable exotic states of matter poised between a crystal and liquid that are endowed with novel thermodynamic and physical properties. The task of formulating an ensemble theory that yields analytical predictions for the structural characteristics and other properties of stealthy degenerate ground states in d -dimensional Euclidean space Rd is highly nontrivial because the dimensionality of the configuration space depends on the number density ρ and there is a multitude of ways of sampling the ground-state manifold, each with its own probability measure for finding a particular ground-state configuration. The purpose of this paper is to take some initial steps in this direction. Specifically, we derive general exact relations for thermodynamic properties (energy, pressure, and isothermal compressibility) that apply to any ground-state ensemble as a function of ρ in any d , and we show how disordered degenerate ground states arise as part of the ground-state manifold. We also derive exact integral conditions that both the pair correlation function g2(r ) and structure factor S (k ) must obey for any d . We then specialize our results to the canonical ensemble (in the zero-temperature limit) by exploiting an ansatz that stealthy states behave remarkably like "pseudo"-equilibrium hard-sphere systems in Fourier space. Our theoretical predictions for g2(r ) and S (k ) are in excellent agreement with computer simulations across the first three space dimensions. These results are used to obtain order metrics, local number variance, and nearest-neighbor functions across dimensions. We also derive accurate analytical
NASA Astrophysics Data System (ADS)
Dineykhan, M.; Zhaugasheva, S. A.; Bekbaev, A. K.; Ishmukhamedov, I. S.
2012-12-01
On the basis of determination of the asymptotic behavior of correlation functions of the corresponding field currents with the corresponding quantum numbers an analytic method for determination of the energy spectrum of three-body Coulomb system is suggested. Our results show that the constituent masses of particles, which we have defined as masses of particles in a bound state, differ from masses of particles in a free-state. The constituent mass to the free state mass relation for the electron is greater than the same mass relation for the proton, deuteron and triton. It was also found that this constituent electron mass has different values in each systems, i.e. in H{2/+}, D{2/+} and T{2/+} hydrogen molecular ions. The contributions of exchange and self-energy diagrams were taken into account in the determination of the energy spectrum of the three-body Coulomb system. Our results show that the self-energy diagram contribution is inversely proportional to the square of the constituent mass of particles. This contribution is sufficient for the electron and is negligible for the proton, deuteron and triton. When defining the energy and the wave function (WF), it is necessary to take into account the contributions of both the exchange and self-energy diagrams.
Wang, Qisi; Shen, Yao; Pan, Bingying; Zhang, Xiaowen; Ikeuchi, K.; Iida, K.; Christianson, A. D.; Walker, H. C.; Adroja, D. T.; Abdel-Hafiez, M.; Chen, Xiaojia; Chareev, D. A.; Vasiliev, A. N.; Zhao, Jun
2016-01-01
Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts=90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ∼60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S=1 nematic quantum-disordered paramagnet interpolating between the Néel and stripe magnetic instabilities. PMID:27431986
Magnetic ground state of FeSe.
Wang, Qisi; Shen, Yao; Pan, Bingying; Zhang, Xiaowen; Ikeuchi, K; Iida, K; Christianson, A D; Walker, H C; Adroja, D T; Abdel-Hafiez, M; Chen, Xiaojia; Chareev, D A; Vasiliev, A N; Zhao, Jun
2016-01-01
Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts=90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ∼60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S=1 nematic quantum-disordered paramagnet interpolating between the Néel and stripe magnetic instabilities. PMID:27431986
The ground state construction of bilayer graphene
NASA Astrophysics Data System (ADS)
Giuliani, Alessandro; Jauslin, Ian
2016-09-01
We consider a model of half-filled bilayer graphene, in which the three dominant Slonczewski-Weiss-McClure hopping parameters are retained, in the presence of short-range interactions. Under a smallness assumption on the interaction strength U as well as on the inter-layer hopping ɛ, we construct the ground state in the thermodynamic limit, and prove that the pressure and two-point Schwinger function, away from its singularities, are analytic in U, uniformly in ɛ. The interacting Fermi surface is degenerate, and consists of eight Fermi points, two of which are protected by symmetries, while the locations of the other six are renormalized by the interaction, and the effective dispersion relation at the Fermi points is conical. The construction reveals the presence of different energy regimes, where the effective behavior of correlation functions changes qualitatively. The analysis of the crossover between regimes plays an important role in the proof of analyticity and in the uniform control of the radius of convergence. The proof is based on a rigorous implementation of fermionic renormalization group methods, including determinant estimates for the renormalized expansion.
Strangeness in the baryon ground states
NASA Astrophysics Data System (ADS)
Semke, A.; Lutz, M. F. M.
2012-10-01
We compute the strangeness content of the baryon octet and decuplet states based on an analysis of recent lattice simulations of the BMW, PACS, LHPC and HSC groups for the pion-mass dependence of the baryon masses. Our results rely on the relativistic chiral Lagrangian and large-Nc sum rule estimates of the counter terms relevant for the baryon masses at N3LO. A partial summation is implied by the use of physical baryon and meson masses in the one-loop contributions to the baryon self energies. A simultaneous description of the lattice results of the BMW, LHPC, PACS and HSC groups is achieved. From a global fit we determine the axial coupling constants F ≃ 0.45 and D ≃ 0.80 in agreement with their values extracted from semi-leptonic decays of the baryons. Moreover, various flavor symmetric limits of baron octet and decuplet masses as obtained by the QCDSF-UKQCD group are recovered. We predict the pion- and strangeness sigma terms and the pion-mass dependence of the octet and decuplet ground states at different strange quark masses.
Freimuth, Frank; Blügel, Stefan; Mokrousov, Yuriy
2016-08-10
Using the Kubo linear-response formalism we derive expressions to calculate the electronic contribution to the heat current generated by magnetization dynamics in ferromagnetic metals with broken inversion symmetry and spin-orbit interaction (SOI). The effect of producing heat currents by magnetization dynamics constitutes the Onsager reciprocal of the thermal spin-orbit torque (TSOT), i.e. the generation of torques on the magnetization due to temperature gradients. We find that the energy current driven by magnetization dynamics contains a contribution from the Dzyaloshinskii-Moriya interaction (DMI), which needs to be subtracted from the Kubo linear response of the energy current in order to extract the heat current. We show that the expressions of the DMI coefficient can be derived elegantly from the DMI energy current. Guided by formal analogies between the Berry phase theory of DMI on the one hand and the modern theory of orbital magnetization on the other hand we are led to an interpretation of the latter in terms of energy currents as well. Based on ab initio calculations we investigate the electronic contribution to the heat current driven by magnetization dynamics in Mn/W(0 0 1) magnetic bilayers. We predict that fast domain walls drive strong heat currents. PMID:27301682
NASA Astrophysics Data System (ADS)
Freimuth, Frank; Blügel, Stefan; Mokrousov, Yuriy
2016-08-01
Using the Kubo linear-response formalism we derive expressions to calculate the electronic contribution to the heat current generated by magnetization dynamics in ferromagnetic metals with broken inversion symmetry and spin–orbit interaction (SOI). The effect of producing heat currents by magnetization dynamics constitutes the Onsager reciprocal of the thermal spin–orbit torque (TSOT), i.e. the generation of torques on the magnetization due to temperature gradients. We find that the energy current driven by magnetization dynamics contains a contribution from the Dzyaloshinskii–Moriya interaction (DMI), which needs to be subtracted from the Kubo linear response of the energy current in order to extract the heat current. We show that the expressions of the DMI coefficient can be derived elegantly from the DMI energy current. Guided by formal analogies between the Berry phase theory of DMI on the one hand and the modern theory of orbital magnetization on the other hand we are led to an interpretation of the latter in terms of energy currents as well. Based on ab initio calculations we investigate the electronic contribution to the heat current driven by magnetization dynamics in Mn/W(0 0 1) magnetic bilayers. We predict that fast domain walls drive strong heat currents.
NASA Astrophysics Data System (ADS)
Freimuth, Frank; Blügel, Stefan; Mokrousov, Yuriy
2016-08-01
Using the Kubo linear-response formalism we derive expressions to calculate the electronic contribution to the heat current generated by magnetization dynamics in ferromagnetic metals with broken inversion symmetry and spin-orbit interaction (SOI). The effect of producing heat currents by magnetization dynamics constitutes the Onsager reciprocal of the thermal spin-orbit torque (TSOT), i.e. the generation of torques on the magnetization due to temperature gradients. We find that the energy current driven by magnetization dynamics contains a contribution from the Dzyaloshinskii-Moriya interaction (DMI), which needs to be subtracted from the Kubo linear response of the energy current in order to extract the heat current. We show that the expressions of the DMI coefficient can be derived elegantly from the DMI energy current. Guided by formal analogies between the Berry phase theory of DMI on the one hand and the modern theory of orbital magnetization on the other hand we are led to an interpretation of the latter in terms of energy currents as well. Based on ab initio calculations we investigate the electronic contribution to the heat current driven by magnetization dynamics in Mn/W(0 0 1) magnetic bilayers. We predict that fast domain walls drive strong heat currents.
Nuclear ground-state masses and deformations: FRDM(2012)
Moller, P.; Sierk, A. J.; Ichikawa, T.; Sagawa, H.
2016-03-25
Here, we tabulate the atomic mass excesses and binding energies, ground-state shell-plus-pairing corrections, ground-state microscopic corrections, and nuclear ground-state deformations of 9318 nuclei ranging from 16O to A=339. The calculations are based on the finite-range droplet macroscopic and the folded-Yukawa single-particle microscopic nuclear-structure models, which are completely specified. Relative to our FRDM(1992) mass table in Möller et al. (1995), the results are obtained in the same model, but with considerably improved treatment of deformation and fewer of the approximations that were necessary earlier, due to limitations in computer power. The more accurate execution of the model and the more extensivemore » and more accurate experimental mass data base now available allow us to determine one additional macroscopic-model parameter, the density-symmetry coefficient LL, which was not varied in the previous calculation, but set to zero. Because we now realize that the FRDM is inaccurate for some highly deformed shapes occurring in fission, because some effects are derived in terms of perturbations around a sphere, we only adjust its macroscopic parameters to ground-state masses.« less
Nuclear ground-state masses and deformations: FRDM(2012)
NASA Astrophysics Data System (ADS)
Möller, P.; Sierk, A. J.; Ichikawa, T.; Sagawa, H.
2016-05-01
We tabulate the atomic mass excesses and binding energies, ground-state shell-plus-pairing corrections, ground-state microscopic corrections, and nuclear ground-state deformations of 9318 nuclei ranging from 16O to A = 339. The calculations are based on the finite-range droplet macroscopic and the folded-Yukawa single-particle microscopic nuclear-structure models, which are completely specified. Relative to our FRDM(1992) mass table in Möller et al. (1995), the results are obtained in the same model, but with considerably improved treatment of deformation and fewer of the approximations that were necessary earlier, due to limitations in computer power. The more accurate execution of the model and the more extensive and more accurate experimental mass data base now available allow us to determine one additional macroscopic-model parameter, the density-symmetry coefficient L, which was not varied in the previous calculation, but set to zero. Because we now realize that the FRDM is inaccurate for some highly deformed shapes occurring in fission, because some effects are derived in terms of perturbations around a sphere, we only adjust its macroscopic parameters to ground-state masses.
Ground states of larger nuclei
Pieper, S.C.; Wiringa, R.B.; Pandharipande, V.R.
1995-08-01
The methods used for the few-body nuclei require operations on the complete spin-isospin vector; the size of this vector makes such methods impractical for nuclei with A > 8. During the last few years we developed cluster expansion methods that do not require operations on the complete vector. We use the same Hamiltonians as for the few-body nuclei and variational wave functions of form similar to the few-body wave functions. The cluster expansions are made for the noncentral parts of the wave functions and for the operators whose expectation values are being evaluated. The central pair correlations in the wave functions are treated exactly and this requires the evaluation of 3A-dimensional integrals which are done with Monte Carlo techniques. Most of our effort was on {sup 16}O, other p-shell nuclei, and {sup 40}Ca. In 1993 the Mathematics and Computer Science Division acquired a 128-processor IBM SP which has a theoretical peak speed of 16 Gigaflops (GFLOPS). We converted our program to run on this machine. Because of the large memory on each node of the SP, it was easy to convert the program to parallel form with very low communication overhead. Considerably more effort was needed to restructure the program from one oriented towards long vectors for the Cray computers at NERSC to one that makes efficient use of the cache of the RS6000 architecture. The SP made possible complete five-body cluster calculations of {sup 16}O for the first time; previously we could only do four-body cluster calculations. These calculations show that the expectation value of the two-body potential is converging less rapidly than we had thought, while that of the three-body potential is more rapidly convergent; the net result is no significant change to our predicted binding energy for {sup 16}O using the new Argonne v{sub 18} potential and the Urbana IX three-nucleon potential. This result is in good agreement with experiment.
Borovkov, V I; Beregovaya, I V; Shchegoleva, L N; Potashov, P A; Bagryansky, V A; Molin, Y N
2012-09-14
Paramagnetic spin-lattice relaxation (SLR) in radical cations (RCs) of the cycloalkane series in liquid solution was studied and analyzed from the point of view of the correlation between the relaxation rate and the structure of the adiabatic potential energy surface (PES) of the RCs. SLR rates in the RCs formed in x-ray irradiated n-hexane solutions of the cycloalkanes studied were measured with the method of time-resolved magnetic field effect in the recombination fluorescence of spin-correlated radical ion pairs. Temperature and, for some cycloalkanes, magnetic field dependences of the relaxation rate were determined. It was found that the conventional Redfield theory of the paramagnetic relaxation as applied to the results on cyclohexane RC, gave a value of about 0.2 ps for the correlation time of the perturbation together with an unrealistically high value of 0.1 T in field units for the matrix element of the relaxation transition. The PES structure was obtained with the DFT quantum-chemical calculations. It was found that for all of the cycloalkanes RCs considered, including low symmetric alkyl-substituted ones, the adiabatic PESes were surfaces of pseudorotation due to avoided crossing. In the RCs studied, a correlation between the SLR rate and the calculated barrier height to the pseudorotation was revealed. For RCs with a higher relaxation rate, the apparent activation energies for the SLR were similar to the calculated heights of the barrier. To rationalize the data obtained it was assumed that the vibronic states degeneracy, which is specific for Jahn-Teller active cyclohexane RC, was approximately kept in the RCs of substituted cycloalkanes for the vibronic states with the energies above and close to the barrier height to the pseudorotation. It was proposed that the effective spin-lattice relaxation in a radical with nearly degenerate low-lying vibronic states originated from stochastic crossings of the vibronic levels that occur due to fluctuations of
Trapped antihydrogen in its ground state.
Gabrielse, G; Kalra, R; Kolthammer, W S; McConnell, R; Richerme, P; Grzonka, D; Oelert, W; Sefzick, T; Zielinski, M; Fitzakerley, D W; George, M C; Hessels, E A; Storry, C H; Weel, M; Müllers, A; Walz, J
2012-03-16
Antihydrogen atoms (H¯) are confined in an Ioffe trap for 15-1000 s-long enough to ensure that they reach their ground state. Though reproducibility challenges remain in making large numbers of cold antiprotons (p¯) and positrons (e(+)) interact, 5±1 simultaneously confined ground-state atoms are produced and observed on average, substantially more than previously reported. Increases in the number of simultaneously trapped H¯ are critical if laser cooling of trapped H¯ is to be demonstrated and spectroscopic studies at interesting levels of precision are to be carried out.
Mizel, Ari
2004-07-01
Ground-state quantum computers mimic quantum-mechanical time evolution within the amplitudes of a time-independent quantum state. We explore the principles that constrain this mimicking. A no-cloning argument is found to impose strong restrictions. It is shown, however, that there is flexibility that can be exploited using quantum teleportation methods to improve ground-state quantum computer design.
First evidence for a virtual 18B ground state
NASA Astrophysics Data System (ADS)
Spyrou, A.; Baumann, T.; Bazin, D.; Blanchon, G.; Bonaccorso, A.; Breitbach, E.; Brown, J.; Christian, G.; DeLine, A.; DeYoung, P. A.; Finck, J. E.; Frank, N.; Mosby, S.; Peters, W. A.; Russel, A.; Schiller, A.; Strongman, M. J.; Thoennessen, M.
2010-01-01
The decay of the neutron unbound ground state of 18B was studied for the first time through a single-proton knockout reaction from a 62 MeV/u 19C beam. The decay energy spectrum was reconstructed from coincidence measurements between the emitted neutron and the 17B fragment using the MoNA/Sweeper setup. An s-wave line shape was used to describe the experimental spectrum resulting in an upper limit for the scattering length of - 50 fm which corresponds to a decay energy <10 keV. Observing an s-wave decay of 18B provides an experimental verification that the ground state of 19C includes a large s-wave component. The presence of this s-wave component shows that s-d mixing is still present in 18B and that the s1 / 2 orbital has not moved significantly below the d5 / 2 orbital.
Spin-orbit-coupled BEC in a double-well potential: Quantum energy spectrum and flat band
NASA Astrophysics Data System (ADS)
Wang, Wen-Yuan; Cao, Hui; Liu, Jie; Fu, Li-Bin
2015-09-01
Spin-orbit-coupled Bose-Einstein condensates (BECs) provide a powerful platform for studies on physical problems in various fields. Here we study the energy spectrum of a tunable spin-orbit-coupled BEC in a double-well potential with adjustable Raman laser intensity. We find in the single-particle spectrum there is a highly degenerate flat band in the ground state of the BEC, which remains stable against changes of the Raman strength. Many-body interactions between atoms remove this high degeneracy. Analytical results for particular cases are obtained by using the perturbation theory, which are in good agreement with the numerical results.
Simulation of the hydrogen ground state in stochastic electrodynamics
NASA Astrophysics Data System (ADS)
Nieuwenhuizen, Theo M.; Liska, Matthew T. P.
2015-10-01
Stochastic electrodynamics is a classical theory which assumes that the physical vacuum consists of classical stochastic fields with average energy \\frac{1}{2}{{\\hslash }}ω in each mode, i.e., the zero-point Planck spectrum. While this classical theory explains many quantum phenomena related to harmonic oscillator problems, hard results on nonlinear systems are still lacking. In this work the hydrogen ground state is studied by numerically solving the Abraham-Lorentz equation in the dipole approximation. First the stochastic Gaussian field is represented by a sum over Gaussian frequency components, next the dynamics is solved numerically using OpenCL. The approach improves on work by Cole and Zou 2003 by treating the full 3d problem and reaching longer simulation times. The results are compared with a conjecture for the ground state phase space density. Though short time results suggest a trend towards confirmation, in all attempted modellings the atom ionises at longer times.
Room temperature skyrmion ground state stabilized through interlayer exchange coupling
Chen, Gong Schmid, Andreas K.; Mascaraque, Arantzazu; N'Diaye, Alpha T.
2015-06-15
Possible magnetic skyrmion device applications motivate the search for structures that extend the stability of skyrmion spin textures to ambient temperature. Here, we demonstrate an experimental approach to stabilize a room temperature skyrmion ground state in chiral magnetic films via exchange coupling across non-magnetic spacer layers. Using spin polarized low-energy electron microscopy to measure all three Cartesian components of the magnetization vector, we image the spin textures in Fe/Ni films. We show how tuning the thickness of a copper spacer layer between chiral Fe/Ni films and perpendicularly magnetized Ni layers permits stabilization of a chiral stripe phase, a skyrmion phase, and a single domain phase. This strategy to stabilize skyrmion ground states can be extended to other magnetic thin film systems and may be useful for designing skyrmion based spintronics devices.
Alternative ground states enable pathway switching in biological electron transfer
Abriata, Luciano A.; Alvarez-Paggi, Damian; Ledesma, Gabirela N.; Blackburn, Ninian J.; Vila, Alejandro J.; Murgida, Daniel H.
2012-10-10
Electron transfer is the simplest chemical reaction and constitutes the basis of a large variety of biological processes, such as photosynthesis and cellular respiration. Nature has evolved specific proteins and cofactors for these functions. The mechanisms optimizing biological electron transfer have been matter of intense debate, such as the role of the protein milieu between donor and acceptor sites. Here we propose a mechanism regulating long-range electron transfer in proteins. Specifically, we report a spectroscopic, electrochemical, and theoretical study on WT and single-mutant CuA redox centers from Thermus thermophilus, which shows that thermal fluctuations may populate two alternative ground-state electronicmore » wave functions optimized for electron entry and exit, respectively, through two different and nearly perpendicular pathways. In conclusion, these findings suggest a unique role for alternative or “invisible” electronic ground states in directional electron transfer. Moreover, it is shown that this energy gap and, therefore, the equilibrium between ground states can be fine-tuned by minor perturbations, suggesting alternative ways through which protein–protein interactions and membrane potential may optimize and regulate electron–proton energy transduction.« less
Alternative ground states enable pathway switching in biological electron transfer
Abriata, Luciano A.; Álvarez-Paggi, Damián; Ledesma, Gabriela N.; Blackburn, Ninian J.; Vila, Alejandro J.; Murgida, Daniel H.
2012-01-01
Electron transfer is the simplest chemical reaction and constitutes the basis of a large variety of biological processes, such as photosynthesis and cellular respiration. Nature has evolved specific proteins and cofactors for these functions. The mechanisms optimizing biological electron transfer have been matter of intense debate, such as the role of the protein milieu between donor and acceptor sites. Here we propose a mechanism regulating long-range electron transfer in proteins. Specifically, we report a spectroscopic, electrochemical, and theoretical study on WT and single-mutant CuA redox centers from Thermus thermophilus, which shows that thermal fluctuations may populate two alternative ground-state electronic wave functions optimized for electron entry and exit, respectively, through two different and nearly perpendicular pathways. These findings suggest a unique role for alternative or “invisible” electronic ground states in directional electron transfer. Moreover, it is shown that this energy gap and, therefore, the equilibrium between ground states can be fine-tuned by minor perturbations, suggesting alternative ways through which protein–protein interactions and membrane potential may optimize and regulate electron–proton energy transduction. PMID:23054836
Molecular spectroscopy for ground-state transfer of ultracold RbCs molecules.
Debatin, Markus; Takekoshi, Tetsu; Rameshan, Raffael; Reichsöllner, Lukas; Ferlaino, Francesca; Grimm, Rudolf; Vexiau, Romain; Bouloufa, Nadia; Dulieu, Olivier; Nägerl, Hanns-Christoph
2011-11-14
We perform one- and two-photon high resolution spectroscopy on ultracold samples of RbCs Feshbach molecules with the aim to identify a suitable route for efficient ground-state transfer in the quantum-gas regime to produce quantum gases of dipolar RbCs ground-state molecules. One-photon loss spectroscopy allows us to probe deeply bound rovibrational levels of the mixed excited (A(1)Σ(+)-b(3)Π)0(+) molecular states. Two-photon dark state spectroscopy connects the initial Feshbach state to the rovibronic ground state. We determine the binding energy of the lowest rovibrational level |v'' = 0, J'' = 0> of the X(1)Σ(+) ground state to be D = 3811.5755(16) cm(-1), a 300-fold improvement in accuracy with respect to previous data. We are now in the position to perform stimulated two-photon Raman transfer to the rovibronic ground state. PMID:21853182
Trapping cold ground state argon atoms.
Edmunds, P D; Barker, P F
2014-10-31
We trap cold, ground state argon atoms in a deep optical dipole trap produced by a buildup cavity. The atoms, which are a general source for the sympathetic cooling of molecules, are loaded in the trap by quenching them from a cloud of laser-cooled metastable argon atoms. Although the ground state atoms cannot be directly probed, we detect them by observing the collisional loss of cotrapped metastable argon atoms and determine an elastic cross section. Using a type of parametric loss spectroscopy we also determine the polarizability of the metastable 4s[3/2](2) state to be (7.3±1.1)×10(-39) C m(2)/V. Finally, Penning and associative losses of metastable atoms in the absence of light assisted collisions, are determined to be (3.3±0.8)×10(-10) cm(3) s(-1).
Magnetic properties of ground-state mesons
NASA Astrophysics Data System (ADS)
Šimonis, V.
2016-04-01
Starting with the bag model a method for the study of the magnetic properties (magnetic moments, magnetic dipole transition widths) of ground-state mesons is developed. We calculate the M1 transition moments and use them subsequently to estimate the corresponding decay widths. These are compared with experimental data, where available, and with the results obtained in other approaches. Finally, we give the predictions for the static magnetic moments of all ground-state vector mesons including those containing heavy quarks. We have a good agreement with experimental data for the M1 decay rates of light as well as heavy mesons. Therefore, we expect our predictions for the static magnetic properties ( i.e., usual magnetic moments) to be of sufficiently high quality, too.
Ground-state rotational constants of 12CH 3D
NASA Astrophysics Data System (ADS)
Chackerian, C.; Guelachvili, G.
1980-12-01
An analysis of ground-state combination differences in the ν2( A1) fundamental band of 12CH 3D ( ν0 = 2200.03896 cm -1) has been made to yield values for the rotational constants B0, D0J, D0JK, H0JJJ, H0JJK, H0JKK, LJJJJ, L0JJJK, and order of magnitude values for L0JJKK and L0JKKK. These constants should be useful in assisting radio searches for this molecule in astrophysical sources. In addition, splittings of A1A2 levels ( J ≥ 17, K = 3) have been measured in both the ground and excited vibrational states of this band.
New Measurement of the 5H Ground State
NASA Astrophysics Data System (ADS)
McNeel, Daniel G.; Wuosmaa, A. H.; Bedoor, S.; Newton, A. S.; Brown, K. W.; Charity, R. J.; Sobotka, L. G.; Buhro, W. W.; Chajecki, Z.; Lynch, W. G.; Manfredi, J.; Showalter, R. H.; Tsang, M. B.; Winklebauer, J. R.; Marley, S. T.; Shetty, D. V.
2015-10-01
We have studied the ground state of 5H using the 6He(d,3He)5H reaction in inverse kinematics. Existing data for 5H are in conflict with each other and with many theoretical predictions. This measurement provides a clear evidence for the 5H ground state, and the previously unreported 6He(d,t)5Heg.s. reaction is also observed. A 6He beam at 55 MeV/A produced at the National Superconducting Cyclotron Laboratory at Michigan State University bombarded a 1.9 mg/cm2 (CD2)n target. The reaction products were detected with HiRA (the High Resolution Array). The 3He and 3H particles from the 6He(d,3He/3H)5H/5He reactions were detected in coincidence with the decay products of the unstable 5H and 5He nuclei, providing signatures for the transitions of interest. The properties of the 5He ground state provide information about the calibration and response of the apparatus. Details of the measurement, and a comparison of the data with earlier results and theoretical calculations, will be presented. Work supported by the U.S. Department of Energy under Contracts DE-FG02-04ER41320 and DE-FG02-87ER40316, and the U. S. National Science Foundation under Grant Numbers PHY-1068217 and PHY-1068192.
Mixed configuration ground state in iron(II) phthalocyanine
NASA Astrophysics Data System (ADS)
Fernández-Rodríguez, Javier; Toby, Brian; van Veenendaal, Michel
2015-06-01
We calculate the angular dependence of the x-ray linear and circular dichroism at the L2 ,3 edges of α -Fe(II) Phthalocyanine (FePc) thin films using a ligand-field model with full configuration interaction. We find the best agreement with the experimental spectra for a mixed ground state of 3Eg(a1g 2eg3b2g 1) and 3B2 g(a1g 1eg4b2g 1) with the two configurations coupled by the spin-orbit interaction. The 3Eg(b ) and 3B2 g states have easy-axis and easy-plane anisotropies, respectively. Our model accounts for an easy-plane magnetic anisotropy and the measured magnitudes of the in-plane orbital and spin moments. The proximity in energy of the two configurations allows a switching of the magnetic anisotropy from easy plane to easy axis with a small change in the crystal field, as recently observed for FePc adsorbed on an oxidized Cu surface. We also discuss the possibility of a quintet ground state (5A1 g is 250 meV above the ground state) with planar anisotropy by manipulation of the Fe-C bond length by depositing the complex on a substrate that is subjected to a mechanical strain.
Global Calculations of Ground-State Axial Shape Asymmetry of Nuclei
Moeller, Peter; Bengtsson, Ragnar; Carlsson, B. Gillis; Olivius, Peter; Ichikawa, Takatoshi
2006-10-20
Important insight into the symmetry properties of the nuclear ground-state (gs) shape is obtained from the characteristics of low-lying collective energy-level spectra. In the 1950s, experimental and theoretical studies showed that in the gs many nuclei are spheroidal in shape rather than spherical. Later, a hexadecapole component of the gs shape was identified. In the 1970-1995 time frame, a consensus that reflection symmetry of the gs shape was broken for some nuclei emerged. Here we present the first calculation across the nuclear chart of axial symmetry breaking in the nuclear gs. We show that we fulfill a necessary condition: Where we calculate axial symmetry breaking, characteristic gamma bands are observed experimentally. Moreover, we find that, for those nuclei where axial asymmetry is found, a systematic deviation between calculated and measured masses is removed.
Ground state properties of solid and liquid spin-aligned atomic hydrogen
NASA Technical Reports Server (NTRS)
Danilowicz, R. L.; Dugan, J. V., Jr.; Etters, R. D.
1976-01-01
Calculations of the ground state energy in the solid phase were performed with the aid of a variational approach. The Morse potential form of the atomic triple potential computed by Kolos and Wolniewicz (1965) was employed for the calculations. The ground state energies of both the liquid and solid phases of spin-aligned atomic hydrogen around the volume of the transition are presented in a graph.
Tuning the Ground State Symmetry of Acetylenyl Radicals
2015-01-01
The lowest excited state of the acetylenyl radical, HCC, is a 2Π state, only 0.46 eV above the ground state, 2Σ+. The promotion of an electron from a π bond pair to a singly occupied σ hybrid orbital is all that is involved, and so we set out to tune those orbital energies, and with them the relative energetics of 2Π and 2Σ+ states. A strategy of varying ligand electronegativity, employed in a previous study on substituted carbynes, RC, was useful, but proved more difficult to apply for substituted acetylenyl radicals, RCC. However, π-donor/acceptor substitution is effective in modifying the state energies. We are able to design molecules with 2Π ground states (NaOCC, H2NCC (2A″), HCSi, FCSi, etc.) and vary the 2Σ+–2Π energy gap over a 4 eV range. We find an inconsistency between bond order and bond dissociation energy measures of the bond strength in the Si-containing molecules; we provide an explanation through an analysis of the relevant potential energy curves. PMID:27162981
Tuning the Ground State Symmetry of Acetylenyl Radicals.
Zeng, Tao; Danovich, David; Shaik, Sason; Ananth, Nandini; Hoffmann, Roald
2015-08-26
The lowest excited state of the acetylenyl radical, HCC, is a (2)Π state, only 0.46 eV above the ground state, (2)Σ(+). The promotion of an electron from a π bond pair to a singly occupied σ hybrid orbital is all that is involved, and so we set out to tune those orbital energies, and with them the relative energetics of (2)Π and (2)Σ(+) states. A strategy of varying ligand electronegativity, employed in a previous study on substituted carbynes, RC, was useful, but proved more difficult to apply for substituted acetylenyl radicals, RCC. However, π-donor/acceptor substitution is effective in modifying the state energies. We are able to design molecules with (2)Π ground states (NaOCC, H2NCC ((2)A″), HCSi, FCSi, etc.) and vary the (2)Σ(+)-(2)Π energy gap over a 4 eV range. We find an inconsistency between bond order and bond dissociation energy measures of the bond strength in the Si-containing molecules; we provide an explanation through an analysis of the relevant potential energy curves. PMID:27162981
Tuning the Ground State Symmetry of Acetylenyl Radicals.
Zeng, Tao; Danovich, David; Shaik, Sason; Ananth, Nandini; Hoffmann, Roald
2015-08-26
The lowest excited state of the acetylenyl radical, HCC, is a (2)Π state, only 0.46 eV above the ground state, (2)Σ(+). The promotion of an electron from a π bond pair to a singly occupied σ hybrid orbital is all that is involved, and so we set out to tune those orbital energies, and with them the relative energetics of (2)Π and (2)Σ(+) states. A strategy of varying ligand electronegativity, employed in a previous study on substituted carbynes, RC, was useful, but proved more difficult to apply for substituted acetylenyl radicals, RCC. However, π-donor/acceptor substitution is effective in modifying the state energies. We are able to design molecules with (2)Π ground states (NaOCC, H2NCC ((2)A″), HCSi, FCSi, etc.) and vary the (2)Σ(+)-(2)Π energy gap over a 4 eV range. We find an inconsistency between bond order and bond dissociation energy measures of the bond strength in the Si-containing molecules; we provide an explanation through an analysis of the relevant potential energy curves.
Ground-state Electronic Structure of Actinide Monocarbides and Mononitrides
Petit, Leon; Svane, Axel; Szotek, Zdzislawa; Temmerman, Walter M; Stocks, George Malcolm
2009-01-01
The self-interaction corrected local spin-density approximation is used to investigate the ground-state valency configuration of the actinide ions in the actinide monocarbides, AC (A=U,Np,Pu,Am,Cm), and the actinide mononitrides, AN. The electronic structure is characterized by a gradually increasing degree of f electron localization from U to Cm, with the tendency toward localization being slightly stronger in the (more ionic) nitrides compared to the (more covalent) carbides. The itinerant band picture is found to be adequate for UC and acceptable for UN, while a more complex manifold of competing localized and delocalized f-electron configurations underlies the ground states of NpC, PuC, AmC, NpN, and PuN. The fully localized 5f-electron configuration is realized in CmC (f{sup 7}), CmN (f{sup 7}), and AmN (f{sup 6}). The observed sudden increase in lattice parameter from PuN to AmN is found to be related to the localization transition. The calculated valence electron densities of states are in good agreement with photoemission data.
Proteome Analysis of Ground State Pluripotency
Taleahmad, Sara; Mirzaei, Mehdi; Parker, Lindsay M.; Hassani, Seyedeh-Nafiseh; Mollamohammadi, Sepideh; Sharifi-Zarchi, Ali; Haynes, Paul A.; Baharvand, Hossein; Salekdeh, Ghasem Hosseini
2015-01-01
The differentiation potential of pluripotent embryonic stem cells (ESCs) can be manipulated via serum and medium conditions for direct cellular development or to maintain a naïve ground state. The self-renewal state of ESCs can thus be induced by adding inhibitors of mitogen activated protein kinase (MAPK) and glycogen synthase kinase-3 (Gsk3), known as 2 inhibitors (2i) treatment. We have used a shotgun proteomics approach to investigate differences in protein expressions between 2i- and serum-grown mESCs. The results indicated that 164 proteins were significantly upregulated and 107 proteins downregulated in 2i-grown cells compared to serum. Protein pathways in 2i-grown cells with the highest enrichment were associated with glycolysis and gluconeogenesis. Protein pathways related to organ development were downregulated in 2i-grown cells. In serum-grown ESCs, protein pathways involved in integrin and focal adhesion, and signaling proteins involved in the actin cytoskeleton regulation were enriched. We observed a number of nuclear proteins which were mostly involved in self-renewal maintenance and were expressed at higher levels in 2i compared to serum - Dnmt1, Map2k1, Parp1, Xpo4, Eif3g, Smarca4/Brg1 and Smarcc1/Baf155. Collectively, the results provided an insight into the key protein pathways used by ESCs in the ground state or metastable conditions through 2i or serum culture medium, respectively. PMID:26671762
Ground state of a resonantly interacting Bose gas
Diederix, J. M.; Heijst, T. C. F. van; Stoof, H. T. C.
2011-09-15
We show that a two-channel mean-field theory for a Bose gas near a Feshbach resonance allows for an analytic computation of the chemical potential, and therefore the universal constant {beta}, at unitarity. To improve on this mean-field theory, which physically neglects condensate depletion, we study a variational Jastrow ansatz for the ground-state wave function and use the hypernetted-chain approximation to minimize the energy for all positive values of the scattering length. We also show that other important physical quantities such as Tan's contact and the condensate fraction can be directly obtained from this approach.
Two-electron photoionization of ground-state lithium
Kheifets, A. S.; Fursa, D. V.; Bray, I.
2009-12-15
We apply the convergent close-coupling (CCC) formalism to single-photon two-electron ionization of the lithium atom in its ground state. We treat this reaction as single-electron photon absorption followed by inelastic scattering of the photoelectron on a heliumlike Li{sup +} ion. The latter scattering process can be described accurately within the CCC formalism. We obtain integrated cross sections of single photoionization leading to the ground and various excited states of the Li{sup +} ion as well as double photoionization extending continuously from the threshold to the asymptotic limit of infinite photon energy. Comparison with available experimental and theoretical data validates the CCC model.
First Observation of Ground State Dineutron Decay: Be16
NASA Astrophysics Data System (ADS)
Spyrou, A.; Kohley, Z.; Baumann, T.; Bazin, D.; Brown, B. A.; Christian, G.; Deyoung, P. A.; Finck, J. E.; Frank, N.; Lunderberg, E.; Mosby, S.; Peters, W. A.; Schiller, A.; Smith, J. K.; Snyder, J.; Strongman, M. J.; Thoennessen, M.; Volya, A.
2012-03-01
We report on the first observation of dineutron emission in the decay of Be16. A single-proton knockout reaction from a 53MeV/u B17 beam was used to populate the ground state of Be16. Be16 is bound with respect to the emission of one neutron and unbound to two-neutron emission. The dineutron character of the decay is evidenced by a small emission angle between the two neutrons. The two-neutron separation energy of Be16 was measured to be 1.35(10) MeV, in good agreement with shell model calculations, using standard interactions for this mass region.
Evidence for the Ground-State Resonance of O26
NASA Astrophysics Data System (ADS)
Lunderberg, E.; DeYoung, P. A.; Kohley, Z.; Attanayake, H.; Baumann, T.; Bazin, D.; Christian, G.; Divaratne, D.; Grimes, S. M.; Haagsma, A.; Finck, J. E.; Frank, N.; Luther, B.; Mosby, S.; Nagi, T.; Peaslee, G. F.; Schiller, A.; Snyder, J.; Spyrou, A.; Strongman, M. J.; Thoennessen, M.
2012-04-01
Evidence for the ground state of the neutron-unbound nucleus O26 was observed for the first time in the single proton-knockout reaction from a 82MeV/u F27 beam. Neutrons were measured in coincidence with O24 fragments. O26 was determined to be unbound by 150-150+50keV from the observation of low-energy neutrons. This result agrees with recent shell-model calculations based on microscopic two- and three-nucleon forces.
Structure of best possible strategies for finding ground states
NASA Astrophysics Data System (ADS)
Hoffmann, Karl Heinz; Franz, Astrid; Salamon, Peter
2002-10-01
Finding the ground state of a system with a complex energy landscape is important for many physical problems including protein folding, spin glasses, chemical clusters, and neural networks. Such problems are usually solved by heuristic search methods whose efficacy is judged by empirical performance on selected examples. We present a proof that for a wide range of objective functions threshold accepting is the best possible strategy within a large class of algorithms that simulate random walks on the landscape. In particular, it can perform better than simulated annealing, Tsallis and Glauber statistics.
NASA Astrophysics Data System (ADS)
Long, V. C.; Montague, J. R.; Kozen, A. C.; Wei, X.; Landry, B. R.; Pearson, K. R.; Turnbull, M. M.; Landee, C. P.
2007-03-01
We compare the zero-field and magnetic field-dependent optical spectra of the Haldane chain compound NENB (Ni[en]2NO2BF4; en = C2N2H8) and the paramagnetic compound, Ni(en) 3(ClO4)2,H2O. Due to similar electronic coordination of Ni^2+, the two materials show similar zero-field d-d electronic transitions, including a spin-forbidden (SF) transition at 1.58 eV, overlapping a broad spin-allowed band at 1.45 eV. The relatively greater intensity of the SF band in the Haldane compound suggests activation by a spin exchange mechanism, whereas a spin-orbit coupling origin is likely in the paramagnet. A second narrower SF spin flip transition appears in NENB at 1.66 eV. In both compounds, the SF excitations are sensitive to applied field H. In NENB, the SF intensity is suppressed by H, consistent with behavior of spin exchange-activated bands. In Ni(en)3(ClO4)-2,H2O, the SF field sensitivity appears to combine an energy shift and intensity decrease. Details of the H dependence reflect the magnetic ground state of the material: the field sensitivity commences only above HC 10 T, in the Haldane compound, whereas the field-induced modifications begin immediately at H = 0 T in the paramagnet.
Thermodynamic ground states of platinum metal nitrides
Aberg, D; Sadigh, B; Crowhurst, J; Goncharov, A
2007-10-09
We have systematically studied the thermodynamic stabilities of various phases of the nitrides of the platinum metal elements using density functional theory. We show that for the nitrides of Rh, Pd, Ir and Pt two new crystal structures, in which the metal ions occupy simple tetragonal lattice sites, have lower formation enthalpies at ambient conditions than any previously proposed structures. The region of stability can extend up to 17 GPa for PtN{sub 2}. Furthermore, we show that according to calculations using the local density approximation, these new compounds are also thermodynamically stable at ambient pressure and thus may be the ground state phases for these materials. We further discuss the fact that the local density and generalized gradient approximations predict different values of the absolute formation enthalpies as well different relative stabilities between simple tetragonal and the pyrite or marcasite structures.
Ground states at the filling factors ν = 7 / 3 and 8 / 3 in the second Landau level
NASA Astrophysics Data System (ADS)
Ito, Toru; Shibata, Naokazu; Nomura, Kentaro; Department of Physics, Tohoku University Team
2013-03-01
The Laughlin state successfully describe the fractional quantum Hall state at ν = 1 / 3 in the lowest Landau level. However, it is known that the Laughlin wavefunction has little overlap with the ground state wavefunction at ν = 7 / 3 in the second Landau level. The ground states at ν = 7 / 3 and 8 / 3 are still unknown.To determine the ground states at these fillings, we use the exact diagonalization method and density-matrix renormalization group (DMRG) method. We calculate overlaps between the ground state and the trial wavefunctions, the ground state energies, and the ground-state pair-correlation functions. We find that the ground state wavefunction at ν = 8 / 3 have very high overlap between the parafermion state, and the ground state energy of the parafermion state is lower than that of the Laughlin state. Further, the short-range structures of pair-correlation functions are significantly different from that of the Lauglin state.From these results, we consider that the parafermion state is a strong candidate of the ground state at ν = 7 / 3 and ν = 8 / 3 .
Achieving Higher Energies via Passively Driven X-band Structures
NASA Astrophysics Data System (ADS)
Sipahi, Taylan; Sipahi, Nihan; Milton, Stephen; Biedron, Sandra
2014-03-01
Due to their higher intrinsic shunt impedance X-band accelerating structures significant gradients with relatively modest input powers, and this can lead to more compact particle accelerators. At the Colorado State University Accelerator Laboratory (CSUAL) we would like to adapt this technology to our 1.3 GHz L-band accelerator system using a passively driven 11.7 GHz traveling wave X-band configuration that capitalizes on the high shunt impedances achievable in X-band accelerating structures in order to increase our overall beam energy in a manner that does not require investment in an expensive, custom, high-power X-band klystron system. Here we provide the design details of the X-band structures that will allow us to achieve our goal of reaching the maximum practical net potential across the X-band accelerating structure while driven solely by the beam from the L-band system.
Quantum gas of deeply bound ground state molecules.
Danzl, Johann G; Haller, Elmar; Gustavsson, Mattias; Mark, Manfred J; Hart, Russell; Bouloufa, Nadia; Dulieu, Olivier; Ritsch, Helmut; Nägerl, Hanns-Christoph
2008-08-22
Molecular cooling techniques face the hurdle of dissipating translational as well as internal energy in the presence of a rich electronic, vibrational, and rotational energy spectrum. In our experiment, we create a translationally ultracold, dense quantum gas of molecules bound by more than 1000 wave numbers in the electronic ground state. Specifically, we stimulate with 80% efficiency, a two-photon transfer of molecules associated on a Feshbach resonance from a Bose-Einstein condensate of cesium atoms. In the process, the initial loose, long-range electrostatic bond of the Feshbach molecule is coherently transformed into a tight chemical bond. We demonstrate coherence of the transfer in a Ramsey-type experiment and show that the molecular sample is not heated during the transfer. Our results show that the preparation of a quantum gas of molecules in specific rovibrational states is possible and that the creation of a Bose-Einstein condensate of molecules in their rovibronic ground state is within reach. PMID:18719277
Antibonding hole ground state in InAs quantum dot molecules
Planelles, Josep
2015-01-22
Using four-band k⋅p Hamiltonians, we study how strain and position-dependent effective masses influence hole tunneling in vertically coupled InAs/GaAs quantum dots. Strain reduces the tunneling and hence the critical interdot distance required for the ground state to change from bonding to antibonding. Variable mass has the opposite effect and a rough compensation leaves little affected the critical bonding-to-antibonding ground state crossover. An alternative implementation of the magnetic field in the envelope function Hamiltonian is given which retrieves the experimental denial of possible after growth reversible magnetically induced bonding-to-antibonding ground state transition, predicted by the widely used Luttinger-Kohn Hamiltonian.
Energy bands and gaps near an impurity
NASA Astrophysics Data System (ADS)
Mihóková, E.; Schulman, L. S.
2016-10-01
It has been suggested that in the neighborhood of a certain kind of defect in a crystal there is a bend in the electronic band. We confirm that this is indeed possible using the Kronig-Penney model. Our calculations also have implications for photonic crystals.
On the Stable Ground State of Mackinawite
NASA Astrophysics Data System (ADS)
Kwon, K.; Refson, K.; Sposito, G.
2009-12-01
Mackinawite is a layer type iron monosulfide (FeS) with stacked sheets of edge-sharing FeS4 tetrahedra. An important player in iron and sulfur cycles, mackinawite is one of the first-formed metastable iron sulfides in anoxic environments, transforming into greigite (Fe3S4) and pyrite (FeS2) minerals or elemental sulfur (S0) and iron (Fe0) depending on redox conditions. Mackinawite also affects the mobility and oxidation states of toxic metals such as As, Hg, and Se. The mineral, typically found as a nanoparticle, has been characterized experimentally. Its fundamental conducting and magnetic properties, however, are still controversial; e.g., whether mackinawite is metallic and whether it has magnetic order. Mackinawite is believed to be metallic and without magnetic ordering down at 4 K based on Mössbauer spectroscopy studies. We examined these two issues by applying plane-wave density functional theory (DFT) to FeS geometry optimization under different magnetic orderings. We found that antiferromagnetic ordering among the Fe atoms is the stable ground state of mackinawite. In this presentation, we shall discuss this result and how it relates to previous experimental work.
van Wilderen, Luuk J G W; Clark, Ian P; Towrie, Michael; van Thor, Jasper J
2009-12-24
Multipulse picosecond mid-infrared spectroscopy has been used to study photochemical reactions of the cyanobacterial phytochrome photoreceptor Cph1. Different photophysical schemes have been discussed in the literature to describe the pathways after photoexcitation, particularly, to identify reaction phases that are linked to photoisomerisation and electronic decay in the 1566-1772 cm(-1) region that probes C=C and C=O stretching modes of the tetrapyrrole chromophore. Here, multipulse spectroscopy is employed, where, compared to conventional visible pump-mid-infrared probe spectroscopy, an additional visible pulse is incorporated that interacts with populations that are evolving on the excited- and ground-state potential energy surfaces. The time delays between the pump and the dump pulse are chosen such that the dump pulse interacts with different phases in the reaction process. The pump and dump pulses are at the same wavelength, 640 nm, and are resonant with the Pr ground state as well as with the excited state and intermediates. Because the dump pulse additionally pumps the remaining, partially recovered, and partially oriented ground-state population, theory is developed for estimating the fraction of excited-state molecules. The calculations take into account the model-dependent ground-state recovery fraction, the angular dependence of the population transfer resulting from the finite bleach that occurs with linearly polarized intense femtosecond optical excitation, and the partially oriented population for the dump field. Distinct differences between the results from the experiments that use a 1 or a 14 ps dump time favor a branching evolution from S1 to an excited state or reconfigured chromophore and to a newly identified ground-state intermediate (GSI). Optical dumping at 1 ps shows the instantaneous induced absorption of a delocalized C=C stretching mode at 1608 cm(-1), where the increased cross section is associated with the electronic ground-state
Magnetic Field Measurement with Ground State Alignment
NASA Astrophysics Data System (ADS)
Yan, Huirong; Lazarian, A.
Observational studies of magnetic fields are crucial. We introduce a process "ground state alignment" as a new way to determine the magnetic field direction in diffuse medium. The alignment is due to anisotropic radiation impinging on the atom/ion. The consequence of the process is the polarization of spectral lines resulting from scattering and absorption from aligned atomic/ionic species with fine or hyperfine structure. The magnetic field induces precession and realign the atom/ion and therefore the polarization of the emitted or absorbed radiation reflects the direction of the magnetic field. The atoms get aligned at their low levels and, as the life-time of the atoms/ions we deal with is long, the alignment induced by anisotropic radiation is susceptible to extremely weak magnetic fields (1 G ≳ B ≳ 10^{-15} G). In fact, the effects of atomic/ionic alignment were studied in the laboratory decades ago, mostly in relation to the maser research. Recently, the atomic effect has been already detected in observations from circumstellar medium and this is a harbinger of future extensive magnetic field studies. A unique feature of the atomic realignment is that they can reveal the 3D orientation of magnetic field. In this chapter, we shall review the basic physical processes involved in atomic realignment. We shall also discuss its applications to interplanetary, circumstellar and interstellar magnetic fields. In addition, our research reveals that the polarization of the radiation arising from the transitions between fine and hyperfine states of the ground level can provide a unique diagnostics of magnetic fields in the Epoch of Reionization.
Formation of antihydrogen in the ground state and {ital n}=2 level
Tripathi, S.; Biswas, R.; Sinha, C.
1995-05-01
The cross sections of antihydrogen formation in the ground state and {ital n}=2 level by the impact of antiprotons on the ground state of positronium have been calculated under the framework of the eikonal approximation for incident energy of 30--1000 keV. The excited-state capture cross sections are quite appreciable and are even larger than the ground-state cross sections for impact energies {le}75 keV. The total eikonal cross sections ({sigma}={sigma}{sub 1{ital s}}+{sigma}{sub 2{ital s}}+{sigma}{sub 2{ital p}}) are always higher than the corresponding first-order Born approximation cross section throughout the present energy span.
Resonant two-photon ionization spectroscopy of jet-cooled UN: Determination of the ground state
NASA Astrophysics Data System (ADS)
Matthew, Daniel J.; Morse, Michael D.
2013-05-01
The optical transitions of supersonically cooled uranium nitride (UN) have been investigated in the range from 19 200 to 23 900 cm-1 using resonant two-photon ionization spectroscopy. A large number of bands have been observed, of which seven have been rotationally resolved and analyzed. All are found to arise from the same state, which is presumably the ground state of the molecule. From the analysis of the bands, the ground state has Ω = 3.5, with a bond length of 1.7650(12) Å. Comparisons to the known isovalent molecules are made, and the variations in ground state configuration are explained in terms of the configurational reordering that occurs with changes in the nuclear and ligand charges. It is concluded that the UN molecule is best considered as a U3+N3- species in which the closed shell nitride ligand interacts with a U3+ ion. The ground state of the molecule derives from a U3+ ion in its 7s15f 2 atomic configuration.
Stabilities and defect-mediated lithium-ion conduction in a ground state cubic Li3 N structure
Nguyen, Manh Cuong; Hoang, Khang; Wang, Cai-Zhuang; Ho, Kai-Ming
2016-01-07
A stable ground state structure with cubic symmetry of Li3N (c-Li3N) is found by ab initio initially symmetric random-generated crystal structure search method. Gibbs free energy, calculated within quasi-harmonic approximation, shows that c-Li3N is the ground state structure for a wide range of temperature. The c-Li3N structure has a negative thermal expansion coefficient at temperatures lower than room temperature, due mainly to two transverse acoustic phonon modes. This c-Li3N phase is a semiconductor with an indirect band gap of 1.90 eV within hybrid density functional calculation. We also investigate the migration and energetics of native point defects in c-Li3N, includingmore » lithium and nitrogen vacancies, interstitials, and anti-site defects. Lithium interstitials are found to have a very low migration barrier (~0.12 eV) and the lowest formation energy among all possible defects. Thus, the ionic conduction in c-Li3N is expected to occur via an interstitial mechanism, in contrast to that in the well-known α-Li3N phase which occurs via a vacancy mechanism.« less
Energy Bands and Thermoelectricity of Filled Skutterudite EuRu4As_{12}
NASA Astrophysics Data System (ADS)
Shankar, A.; Rai, D. P.; Sandeep; Khenata, R.; Thapa, R. K.; Mandal, P. K.
2016-11-01
Density functional theory-based calculations of the elastic and electronic properties with magnetic moments of the filled skutterudite EuRu4As_{12} have been performed in its ferromagnetic ground state. The full-potential linearized augmented plane wave (FP-LAPW) method has been used for the study presented here. The numerical values of the elastic parameters are estimated within the framework of the Voigt-Reuss-Hill approximations. The energy band structure calculation performed near the Fermi energy level shows the metallic nature of the material with a high value of Seebeck coefficient ( S). The presence of an exchange splitting of Eu-4 f states suggests their appreciable contribution toward the magnetic behavior. The analysis of the thermal transport properties confirms the result obtained from the electronic structure calculation with Seebeck coefficient of 118 μ{V/K} and the figure of merit ( ZT) value of 0.51, at room temperature. The estimated values of S and ZT indicate the possibility of the thermoelectric applications of the sample material.
Nuclear ground state charge radii from electromagnetic interactions
Frickle, G.; Bernhardt, C.; Heilig, K.
1995-07-01
The Tables summarize experimental results from muonic atom transition energies, nuclear charge parameters from elastic electron scattering, and K x-ray isotope shifts in so far as they provide information on nuclear ground-state charge radii. Numerous experimental results for optical isotope shifts have been published elsewhere; for eight elements the relevant information is condensed ({open_quotes}project{close_quotes}) here to one optical line per element. A model-independent analysis which combines data from all three experimental methods is applied to these elements and is presented as an illustration of the improved accuracy for the rms radii and Barrett radii which result from this analysis. 51 refs., 11 figs, 1 tab.
Ground state magnetic dipole moment of {sup 35}K
Mertzimekis, T.J.; Mantica, P.F.; Liddick, S.N.; Tomlin, B.E.; Davies, A.D.
2006-02-15
The ground state magnetic moment of {sup 35}K has been measured using the technique of nuclear magnetic resonance on {beta}-emitting nuclei. The short-lived {sup 35}K nuclei were produced following the reaction of a {sup 36}Ar primary beam of energy 150 MeV/nucleon incident on a Be target. The spin polarization of the {sup 35}K nuclei produced at 2 deg. relative to the normal primary beam axis was confirmed. Together with the mirror nucleus {sup 35}S, the measurement represents the heaviest T=3/2 mirror pair for which the spin expectation value has been obtained. A linear behavior of g{sub p} vs g{sub n} has been demonstrated for the T=3/2 known mirror moments and the slope and intercept are consistent with the previous analysis of T=1/2 mirror pairs.
Ground states of partially connected binary neural networks
NASA Technical Reports Server (NTRS)
Baram, Yoram
1990-01-01
Neural networks defined by outer products of vectors over (-1, 0, 1) are considered. Patterns over (-1, 0, 1) define by their outer products partially connected neural networks consisting of internally strongly connected, externally weakly connected subnetworks. Subpatterns over (-1, 1) define subnetworks, and their combinations that agree in the common bits define permissible words. It is shown that the permissible words are locally stable states of the network, provided that each of the subnetworks stores mutually orthogonal subwords, or, at most, two subwords. It is also shown that when each of the subnetworks stores two mutually orthogonal binary subwords at most, the permissible words, defined as the combinations of the subwords (one corresponding to each subnetwork), that agree in their common bits are the unique ground states of the associated energy function.
Calculation of electron scattering from the ground state of ytterbium
Bostock, Christopher J.; Fursa, Dmitry V.; Bray, Igor
2011-05-15
We report on the application of the convergent close-coupling method, in both relativistic and nonrelativistic formulations, to electron scattering from ytterbium. Angle-differential and integrated cross sections are presented for elastic scattering and excitation of the states (6s6p){sup 3}P{sub 0,1,2}, (6s6p){sup 1}P{sub 1}{sup o}, (6s7p){sup 1}P{sub 1}{sup o}, and (6s5d){sup 1}D{sub 2}{sup e} for a range of incident electron energies. We also present calculations of the total cross section, and angle-differential Stokes parameters for excitation of the (6s6p){sup 3}P{sub 1}{sup o} state from the ground state. A comparison is made with the relativistic distorted-wave method and experiments.
Unresolved Question of the He10 Ground State Resonance
NASA Astrophysics Data System (ADS)
Kohley, Z.; Snyder, J.; Baumann, T.; Christian, G.; DeYoung, P. A.; Finck, J. E.; Haring-Kaye, R. A.; Jones, M.; Lunderberg, E.; Luther, B.; Mosby, S.; Simon, A.; Smith, J. K.; Spyrou, A.; Stephenson, S. L.; Thoennessen, M.
2012-12-01
The ground state of He10 was populated using a 2p2n-removal reaction from a 59MeV/u Be14 beam. The decay energy of the three-body system, He8+n+n, was measured and a resonance was observed at E=1.60(25)MeV with a 1.8(4) MeV width. This result is in agreement with previous invariant mass spectroscopy measurements, using the Li11(-p) reaction, but is inconsistent with recent transfer reaction results. The proposed explanation that the difference, about 500 keV, is due to the effect of the extended halo nature of Li11 in the one-proton knockout reaction is no longer valid as the present work demonstrates that the discrepancy between the transfer reaction results persists despite using a very different reaction mechanism, Be14(-2p2n).
Ground states of spin-2 condensates in an external magnetic field
Zheng, G.-P.; Tong, Y.-G.; Wang, F.-L.
2010-06-15
The possible ground states of spin-2 Bose-Einstein condensates in an external magnetic field are obtained analytically and classified systematically according to the population of the condensed atoms at the hyperfine sublevels. It is shown that the atoms can populate simultaneously at four hyperfine sublevels in a weak magnetic field with only the linear Zeeman energy, in contrast to that in a stronger magnetic field with the quadratic Zeeman energy, where condensed atoms can at most populate at three hyperfine sublevels in the ground states. Any spin configuration we obtained will give a closed subspace in the order parameter space of the condensates.
Interface Representations of Critical Ground States
NASA Astrophysics Data System (ADS)
Kondev, Jane
1995-01-01
We study the critical properties of the F model, the three-coloring model on the honeycomb lattice, and the four-coloring model on the square lattice, by mapping these models to models of rough interfaces. In particular, we construct operators in a systematic way, which is provided by the interface representation, and we show that their scaling dimensions can be related to the stiffness of the interface. Two types of operators are found, and they correspond to electric and magnetic charges in the Coulomb gas which is related to the interface model by the usual duality transformation. Furthermore, we find that the stiffness of the interface models, and therefore all the critical exponents, can be calculated exactly by considering the contour correlation function which measures the probability that two points on the interface belong to the same contour loop. The exact information about the stiffness also allows us to analyze in detail the conformal field theories (CFT) that represent the scaling limits of the interface models. We find that CFT's associated with the F model, the three -coloring model, and the four-coloring model, have chiral symmetry algebras given by the su(2)_{k=1 }, su(3)_{k=1}, and su(4) _{k=1} Kac-Moody algebras, respectively. The three-coloring and the four coloring-model are ground states of certain antiferromagnetic Potts models, and the behavior of these Potts models at small but finite temperatures is determined by topological defects that can be defined in the associated interface models. In this way we calculate the correlation length and the specific heat of the Potts models, and they are in good agreement with numerical simulations. We also present our Monte-Carlo results for the scaling dimensions of operators in the four-coloring model, and they are in excellent agreement with our analytical results. Finally, we define geometrical exponents for contour loops on self -affine interfaces and calculate their values as a function of the
Interactions leading to disordered ground states and unusual low-temperature behavior.
Batten, Robert D; Stillinger, Frank H; Torquato, Salvatore
2009-09-01
We have shown that any pair potential function v(r) possessing a Fourier transform V(k) that is positive and has compact support at some finite wave number K yields classical disordered ground states for a broad density range [R. D. Batten, F. H. Stillinger, and S. Torquato, J. Appl. Phys. 104, 033504 (2008)]. By tuning a constraint parameter chi (defined in the text), the ground states can traverse varying degrees of local order from fully disordered to crystalline ground states. Here, we show that in two dimensions, the " k -space overlap potential," where V(k) is proportional to the intersection area between two disks of diameter K whose centers are separated by k , yields anomalous low-temperature behavior, which we attribute to the topography of the underlying energy landscape. At T=0 , for the range of densities considered, we show that there is continuous energy degeneracy among Bravais-lattice configurations. The shear elastic constant of ground-state Bravais-lattice configurations vanishes. In the harmonic regime, a significant fraction of the normal modes for both amorphous and Bravais-lattice ground states have vanishing frequencies, indicating the lack of an internal restoring force. Using molecular-dynamics simulations, we observe negative thermal-expansion behavior at low temperatures, where upon heating at constant pressure, the system goes through a density maximum. For all temperatures, isothermal compression reduces the local structure of the system unlike typical single-component systems. PMID:19905060
Jarlborg, T
2014-04-16
The electronic structures of rare-earth elements in the hexagonal close-packed structure and Europium in the body-centered cubic structure are calculated using density-functional theory (DFT). X-ray photoemission spectroscopy (XPS) and bremsstrahlung isochromatic spectroscopy (BIS) simulations are made within DFT by implying that the f-electrons are excited by a large photon energy, either by removal from the occupied states in XPS or by addition to the unoccupied f-states in BIS. The results show sizable differences in the apparent position of the f-states compared to the f-band energy of the ground states. This result is fundamentally different from calculations assuming strong on-site correlation, since all the calculations are based on DFT. The spin-orbit coupling and multiplet splittings are not included, and the present simulation accounts for almost half of the difference between the f-level positions in the DFT ground states and the observed f-level positions. The electronic specific-heat at low T is compatible with the DFT ground state, where f-electrons often reside at the Fermi level.
On the ground state of Yang-Mills theory
Bakry, Ahmed S.; Leinweber, Derek B.; Williams, Anthony G.
2011-08-15
Highlights: > The ground state overlap for sets of meson potential trial states is measured. > Non-uniform gluonic distributions are probed via Wilson loop operator. > The locally UV-regulated flux-tube operators can optimize the ground state overlap. - Abstract: We investigate the overlap of the ground state meson potential with sets of mesonic-trial wave functions corresponding to different gluonic distributions. We probe the transverse structure of the flux tube through the creation of non-uniform smearing profiles for the string of glue connecting two color sources in Wilson loop operator. The non-uniformly UV-regulated flux-tube operators are found to optimize the overlap with the ground state and display interesting features in the ground state overlap.
Ground state of the one-dimensional half-filled Hubbard model
NASA Astrophysics Data System (ADS)
Chashchin, N. I.
2016-07-01
We investigate the ground state ( T = 0 K) of the one-dimensional symmetrical ( n = 1) Hubbard model formalized in terms of the system of integral equations, which we previously obtained using the method of the generating functional of Green's functions with the subsequent Legendre transformation. In a wide range of variations in the parameter of Coulomb interaction U, the following characteristics of the system have been calculated: the electron density of states, the electron band spectrum, the number of doubly occupied lattice sites, the localized magnetic moment, the correlator of the square of the longitudinal component of spin at a site,< S Z 2>, and the internal energy of the system. It has been shown that, for all U > 0, the model yields two solutions, i.e., an antiferromagnetic insulator and a paramagnetic insulator, in which there are no single-electron quasi-particles at the Fermi level. The energy of the paramagnetic solution in the region of U < 1.1 is considerably less than that of the antiferromagnetic solution for the case of U > 1.1, we have the opposite situation.
Exact ground states and topological order in interacting Kitaev/Majorana chains
NASA Astrophysics Data System (ADS)
Katsura, Hosho; Schuricht, Dirk; Takahashi, Masahiro
2015-09-01
We study a system of interacting spinless fermions in one dimension that, in the absence of interactions, reduces to the Kitaev chain [Kitaev, Phys. Usp. 44, 131 (2001), 10.1070/1063-7869/44/10S/S29]. In the noninteracting case, a signal of topological order appears as zero-energy modes localized near the edges. We show that the exact ground states can be obtained analytically even in the presence of nearest-neighbor repulsive interactions when the on-site (chemical) potential is tuned to a particular function of the other parameters. As with the noninteracting case, the obtained ground states are twofold degenerate and differ in fermionic parity. We prove the uniqueness of the obtained ground states and show that they can be continuously deformed to the ground states of the noninteracting Kitaev chain without gap closing. We also demonstrate explicitly that there exists a set of operators each of which maps one of the ground states to the other with opposite fermionic parity. These operators can be thought of as an interacting generalization of Majorana edge zero modes.
A projection gradient method for computing ground state of spin-2 Bose–Einstein condensates
Wang, Hanquan
2014-10-01
In this paper, a projection gradient method is presented for computing ground state of spin-2 Bose–Einstein condensates (BEC). We first propose the general projection gradient method for solving energy functional minimization problem under multiple constraints, in which the energy functional takes real functions as independent variables. We next extend the method to solve a similar problem, where the energy functional now takes complex functions as independent variables. We finally employ the method into finding the ground state of spin-2 BEC. The key of our method is: by constructing continuous gradient flows (CGFs), the ground state of spin-2 BEC can be computed as the steady state solution of such CGFs. We discretized the CGFs by a conservative finite difference method along with a proper way to deal with the nonlinear terms. We show that the numerical discretization is normalization and magnetization conservative and energy diminishing. Numerical results of the ground state and their energy of spin-2 BEC are reported to demonstrate the effectiveness of the numerical method.
Ordering and Magnetism in Fe-Co: Dense Sequence of Ground-State Structures
NASA Astrophysics Data System (ADS)
Drautz, Ralf; Díaz-Ortiz, Alejandro; Fähnle, Manfred; Dosch, Helmut
2004-08-01
We discover that Fe-Co alloys develop a series of ordered ground-state structures in addition to the known CsCl-type structure. This new set of structures is found from a combinatorial ground-state search of 1.5×1010 bcc-based structures. The energies of the searched bcc structures are constructed with the cluster expansion method from few first-principles calculations of ordered Fe-Co structures. The set of new ground-state structures is explained from the decay behavior of the cluster expansion coefficients which allows us to identify a simple geometric motif common to all structures. The appearance of these FeCo superstructures offers a broader view of the ordering reactions in bipartite-lattice based binary alloys.
Trajectory approach to the Schrödinger-Langevin equation with linear dissipation for ground states
NASA Astrophysics Data System (ADS)
Chou, Chia-Chun
2015-11-01
The Schrödinger-Langevin equation with linear dissipation is integrated by propagating an ensemble of Bohmian trajectories for the ground state of quantum systems. Substituting the wave function expressed in terms of the complex action into the Schrödinger-Langevin equation yields the complex quantum Hamilton-Jacobi equation with linear dissipation. We transform this equation into the arbitrary Lagrangian-Eulerian version with the grid velocity matching the flow velocity of the probability fluid. The resulting equation is simultaneously integrated with the trajectory guidance equation. Then, the computational method is applied to the harmonic oscillator, the double well potential, and the ground vibrational state of methyl iodide. The excellent agreement between the computational and the exact results for the ground state energies and wave functions shows that this study provides a synthetic trajectory approach to the ground state of quantum systems.
Ground state and magnetic susceptibility of intermediate-valence Tm impurities
NASA Astrophysics Data System (ADS)
Allub, R.; Aligia, A. A.
1995-09-01
We consider the appropriate generalization of the Anderson model for a Tm impurity in a cubic crystal field. In the 4f12 configuration we include only the two multiplets of lowest energy: a single Γ1 and a triplet Γ4. Similarly we include only the doublet ground state of the 4f13 configuration, and (to make our numerical method feasible) we assume that the conduction-electron partial waves with symmetry Γ8 can be neglected. We study the model using Wilson's renormalization group. The resulting ground state is a singlet or a doublet depending mainly of the relative strength of the hybridization of the 4f13 doublet with both 4f12 states. A doublet ground state is consistent with the experimental evidence.
Traces of Lorentz symmetry breaking in a hydrogen atom at ground state
NASA Astrophysics Data System (ADS)
Borges, L. H. C.; Barone, F. A.
2016-02-01
Some traces of a specific Lorentz symmetry breaking scenario in the ground state of the hydrogen atom are investigated. We use standard Rayleigh-Schrödinger perturbation theory in order to obtain the corrections to the ground state energy and the wave function. It is shown that an induced four-pole moment arises, due to the Lorentz symmetry breaking. The model considered is the one studied in Borges et al. (Eur Phys J C 74:2937, 2014), where the Lorentz symmetry is broken in the electromagnetic sector.
Ground-state and finite-temperature energetics and topologies of germanium microclusters
Antonio, G.A.; Feuston, B.P.; Kalia, R.K.; Vashishta, P.
1988-06-15
We have investigated the ground-state and finite-temperature properties of Ge microclusters (N = 2 to 14) using molecular dynamics (MD) simulation along with the method of steepest-descent quench (SDQ). The interaction potential adopted is the three-body Stillinger--Weber potential as modified by Ding and Andersen for amorphous Ge. Our results indicate that the experimentally observed greater stability of certain cluster sizes can be explained by the topology and energetics of the clusters at finite temperature rather than by the binding energies of the ground-state structures.
Ground State of Magnetic Dipoles on a Two-Dimensional Lattice: Structural Phases in Complex Plasmas
Feldmann, J. D.; Kalman, G. J.; Hartmann, P.; Rosenberg, M.
2008-02-29
We study analytically and by molecular dynamics simulations the ground state configuration of a system of magnetic dipoles fixed on a two-dimensional lattice. We find different phases, in close agreement with previous results. Building on this result and on the minimum energy requirement we determine the equilibrium lattice configuration, the magnetic order (ferromagnetic versus antiferromagnetic), and the magnetic polarization direction of a system of charged mesoscopic particles with magnetic dipole moments, in the domain where the strong electrostatic coupling leads to a crystalline ground state. Orders of magnitudes of the parameters of the system relevant to possible future dusty plasma experiments are discussed.
Ground-state properties of third-row elements with nonlocal density functionals
Bagno, P.; Jepsen, O.; Gunnarsson, O.
1989-07-15
The cohesive energy, the lattice parameter, and the bulk modulus of third-row elements are calculated using the Langreth-Mehl-Hu (LMH), the Perdew-Wang (PW), and the gradient expansion functionals. The PW functional is found to give somewhat better results than the LMH functional and both are found to typically remove half the errors in the local-spin-density (LSD) approximation, while the gradient expansion gives worse results than the local-density approximation. For Fe both the LMH and PW functionals correctly predict a ferromagnetic bcc ground state, while the LSD approximation and the gradient expansion predict a nonmagnetic fcc ground state.
Robinson, A P; Woods, P J; Seweryniak, D; Davids, C N; Carpenter, M P; Hecht, A A; Peterson, D; Sinha, S; Walters, W B; Zhu, S
2005-07-15
Ground-state proton radioactivity has been identified from 121Pr. A transition with a proton energy of E(p)=882(10) keV [Q(p)=900(10) keV] and half-life t(1/2)=10(+6)(-3) ms has been observed and is assigned to the decay of a highly prolate deformed 3/2(+) or 3/2(-) Nilsson state. The present result is found to be incompatible with a previously reported observation of ground-state proton radioactivity from 121Pr, which would have represented the discovery of this phenomenon.
Preparing Ground States of Quantum Many-Body Systems on a Quantum Computer
Poulin, David; Wocjan, Pawel
2009-04-03
Preparing the ground state of a system of interacting classical particles is an NP-hard problem. Thus, there is in general no better algorithm to solve this problem than exhaustively going through all N configurations of the system to determine the one with lowest energy, requiring a running time proportional to N. A quantum computer, if it could be built, could solve this problem in time {radical}(N). Here, we present a powerful extension of this result to the case of interacting quantum particles, demonstrating that a quantum computer can prepare the ground state of a quantum system as efficiently as it does for classical systems.
Green's function Monte Carlo calculation for the ground state of helium trimers
Cabral, F.; Kalos, M.H.
1981-02-01
The ground state energy of weakly bound boson trimers interacting via Lennard-Jones (12,6) pair potentials is calculated using a Monte Carlo Green's Function Method. Threshold coupling constants for self binding are obtained by extrapolation to zero binding.
Energies of 4f^N and 4f^N-15d States Relative to Host Bands in Rare-earth-doped Fluorides
NASA Astrophysics Data System (ADS)
Thiel, C. W.; Joubert, M.-F.; Tkachuk, A.
2005-03-01
Energies of 4f^N states relative to crystal band states were measured for rare-earth ions in the optical host materials LiYF4, Na0.4Y0.6F2.2, and LaF3 using x-ray photoemission spectroscopy. Spectra were modeled to determine the valence band maximum and 4f^ electron binding energies in each material. These results were combined with 4f^N to 4f^N-15d transition energies to determine 5d binding energies for the lowest levels of excited 4f^N-15d configurations. While 4f^N ground-state energies vary within several eV of the valence band maximum for different rare-earth ions in each host, the lowest 4f^N-15d states have similar energies and are several eV below the bottom of the conduction band. A simple model accurately described 4f^N and 4f^N-15d binding energies across the entire series of rare-earth ions. These results improve the understanding of optical materials for lasers, phosphors, and spectral hole burning applications for optical signal processing and data storage.
Ground state of the U2Mo compound: Physical properties of the Ω-phase
NASA Astrophysics Data System (ADS)
Losada, E. L.; Garcés, J. E.
2016-10-01
Using ab initio calculations, unexpected structural instability was recently found in the ground state of the U2 Mo compound. Instead of the unstable I4/mmm and the Pmmn structures, in this work the P6/mmm (#191) space group, usually called Ω-phase, is proposed as the fundamental state. Total energy calculations using Wien2k code slightly favoured the last structure. Electronic and elastic properties are studied in this work in order to characterize the physical properties of this new phase. The stability of the Ω-phase is studied by means of its elastic constants calculation and phonon dispersion spectrum. Analysis of isotropic indices shows that the new phase is a ductile material with a minimal degree of anisotropy, suggesting that U2 Mo in the P6/mmm structure is an elastic isotropic material. Analysis of charge density, density of electronic states (DOS) and the character of the bands revealed a high level of hybridization between d-molybdenum electronic states and d- and f-uranium ones.
NASA Astrophysics Data System (ADS)
Usuki, Takanori; Matsuochi, Kouki; Nakamura, Tsubasa; Toprasertpong, Kasidit; Fukuyama, Atsuhiko; Sugiyama, Masakazu; Nakano, Yoshiaki; Ikari, Tetsuo
2016-03-01
Multiple Quantum wells (MQWs) have been studied as one promising material for high-efficiency nextgeneration solar cells. However, a portion of photo-excited carriers recombine in MQWs, resulting in the degradation of cell performance. Super-lattice (SL) structures, where quantum states in neighboring quantum wells strongly couple with each other, have been proposed for the carrier collection improvement via the tunneling transport through mini-bands. Therefore, it is important to characterize mini-band formation in various types of SL structures. We examined p-i-n GaAs-based solar cells whose i layers contain 20 stacks of InGaAs/GaAsP MQW structures with 2.1-nm GaAsP barriers (thin-barrier cell), with 2.1-nm barriers and 3-nm GaAs interlayers in between GaAsP barriers and InGaAs wells (stepbarrier cell), and with 7.8-nm barriers (thick-barrier cell). We investigated the optical absorption spectra of the SL solar cells using piezoelectric photo-thermal (PPT) spectroscopy. In the thick-barrier cell, one exciton peak was observed near the absorption edge of MQWs. On the other hand, we confirmed a split of the exciton peak for the thin-barrier SL, suggesting the formation of mini-band. Moreover, in the step-barrier cell, the mini-band at the ground state disappears since thick GaAs interlayers isolate each quantum-well ground state and, instead, the mini-band formation of highenergy states could be observed. By estimating from the energy-level calculation, this is attributed to the mini-band formation of light-hole states. This can well explain the improvement of carrier collection efficiency (CCE) of the thinbarrier and the step-barrier cells compared with the thick-barrier cell.
Approximating the ground state of gapped quantum spin systems
Michalakis, Spyridon; Hamza, Eman; Nachtergaele, Bruno; Sims, Robert
2009-01-01
We consider quantum spin systems defined on finite sets V equipped with a metric. In typical examples, V is a large, but finite subset of Z{sup d}. For finite range Hamiltonians with uniformly bounded interaction terms and a unique, gapped ground state, we demonstrate a locality property of the corresponding ground state projector. In such systems, this ground state projector can be approximated by the product of observables with quantifiable supports. In fact, given any subset {chi} {contained_in} V the ground state projector can be approximated by the product of two projections, one supported on {chi} and one supported on {chi}{sup c}, and a bounded observable supported on a boundary region in such a way that as the boundary region increases, the approximation becomes better. Such an approximation was useful in proving an area law in one dimension, and this result corresponds to a multi-dimensional analogue.
Effect of spin-orbit coupling on the ground state structure of mercury
NASA Astrophysics Data System (ADS)
Mishra, Vinayak; Gyanchandani, Jyoti; Chaturvedi, Shashank; Sikka, S. K.
2014-05-01
Near zero kelvin ground state structure of mercury is the body centered tetragonal (BCT) structure (β Hg). However, in all previously reported density functional theory (DFT) calculations, either the rhombohedral or the HCP structure has been found to be the ground state structure. Based on the previous calculations it was predicted that the correct treatment of the SO effects would improve the result. We have performed FPLAPW calculations, with and without inclusion of the SO coupling, for determining the ground state structure. These calculations determine rhombohedral structure as the ground state structure instead of BCT structure. The calculations, without inclusion of SO effect, predict that the energies of rhombohedral and BCT structures are very close to each other but the energy of rhombohedral structure is lower than that of BCT structure at ambient as well as high pressure. On the contrary, the SO calculations predict that though at ambient conditions the rhombohedral structure is the stable structure but on applying a pressure of 3.2 GPa, the BCT structure becomes stable. Hence, instead of predicting the stability of BCT structure at zero pressure, the SO calculations predict its stability at 3.2 GPa. This small disagreement is expected when the energy differences between the structures are small.
Tunable ground states in helical p-wave Josephson junctions
NASA Astrophysics Data System (ADS)
Cheng, Qiang; Zhang, Kunhua; Yu, Dongyang; Chen, Chongju; Zhang, Yinhan; Jin, Biao
2016-07-01
We study new types of Josephson junctions composed of helical p-wave superconductors with {k}x\\hat{x}+/- {k}y\\hat{y} and {k}y\\hat{x}+/- {k}x\\hat{y}-pairing symmetries using quasi-classical Green’s functions with generalized Riccati parametrization. The junctions can host rich ground states: π phase, 0 + π phase, φ 0 phase and φ phase. The phase transition can be tuned by rotating the magnetization in the ferromagnetic interface. We present the phase diagrams in the parameter space formed by the orientation of the magnetization or by the magnitude of the interfacial potentials. The selection rules for the lowest order current which are responsible for the formation of the rich phases are summarized from the current-phase relations based on the numerical calculation. We construct a Ginzburg–Landau type of free energy for the junctions with d-vectors and the magnetization, which not only reveals the interaction forms of spin-triplet superconductivity and ferromagnetism, but can also directly lead to the selection rules. In addition, the energies of the Andreev bound states and the novel symmetries in the current-phase relations are also investigated. Our results are helpful both in the prediction of novel Josephson phases and in the design of quantum circuits.
Tunable ground states in helical p-wave Josephson junctions
NASA Astrophysics Data System (ADS)
Cheng, Qiang; Zhang, Kunhua; Yu, Dongyang; Chen, Chongju; Zhang, Yinhan; Jin, Biao
2016-07-01
We study new types of Josephson junctions composed of helical p-wave superconductors with {k}x\\hat{x}+/- {k}y\\hat{y} and {k}y\\hat{x}+/- {k}x\\hat{y}-pairing symmetries using quasi-classical Green’s functions with generalized Riccati parametrization. The junctions can host rich ground states: π phase, 0 + π phase, φ 0 phase and φ phase. The phase transition can be tuned by rotating the magnetization in the ferromagnetic interface. We present the phase diagrams in the parameter space formed by the orientation of the magnetization or by the magnitude of the interfacial potentials. The selection rules for the lowest order current which are responsible for the formation of the rich phases are summarized from the current-phase relations based on the numerical calculation. We construct a Ginzburg-Landau type of free energy for the junctions with d-vectors and the magnetization, which not only reveals the interaction forms of spin-triplet superconductivity and ferromagnetism, but can also directly lead to the selection rules. In addition, the energies of the Andreev bound states and the novel symmetries in the current-phase relations are also investigated. Our results are helpful both in the prediction of novel Josephson phases and in the design of quantum circuits.
Ground state of Ho atoms on Pt(111) metal surfaces: Implications for magnetism
NASA Astrophysics Data System (ADS)
Karbowiak, M.; Rudowicz, C.
2016-05-01
We investigated the ground state of Ho atoms adsorbed on the Pt(111) surface, for which conflicting results exist. The density functional theory (DFT) calculations yielded the Ho ground state as | Jz=±8 > . Interpretation of x-ray absorption spectroscopy and x-ray magnetic circular dichroism spectra and the magnetization curves indicated the ground state as | Jz=±6 > . Superposition model is employed to predict the crystal-field (CF) parameters based on the structural data for the system Ho/Pt(111) obtained from the DFT modeling. Simultaneous diagonalization of the free-ion (HFI) and the trigonal CF Hamiltonian (HCF) within the whole configuration 4 f10 of H o3 + ion was performed. The role of the trigonal CF terms, neglected in the pure uniaxial CF model used previously for interpretation of experimental spectra, is found significant, whereas the sixth-rank CF terms may be neglected in agreement with the DFT predictions. The results provide substantial support for the experimental designation of the | Jz=±6 > ground state, albeit with subtle difference due to admixture of other | Jz> states, but run against the DFT-based designation of the | Jz=±8 > ground state. A subtle splitting of the ground energy level with the state (predominantly), | Jz=±6 > is predicted. This paper provides better insight into the single-ion magnetic behavior of the Ho/Pt(111) system by helping to resolve the controversy concerning the Ho ground state. Experimental techniques with greater resolution powers are suggested for direct confirmation of this splitting and C3 v symmetry experienced by the Ho atom.
Three-body correlations in the ground-state decay of 26O
NASA Astrophysics Data System (ADS)
Kohley, Z.; Baumann, T.; Christian, G.; DeYoung, P. A.; Finck, J. E.; Frank, N.; Luther, B.; Lunderberg, E.; Jones, M.; Mosby, S.; Smith, J. K.; Spyrou, A.; Thoennessen, M.
2015-03-01
Background: Theoretical calculations have shown that the energy and angular correlations in the three-body decay of the two-neutron unbound 26O can provide information on the ground-state wave function, which has been predicted to have a dineutron configuration and 2 n halo structure. Purpose: To use the experimentally measured three-body correlations to gain insight into the properties of 26O , including the decay mechanism and ground-state resonance energy. Method: 26O was produced in a one-proton knockout reaction from 27F and the 24O+n +n decay products were measured using the MoNA-Sweeper setup. The three-body correlations from the 26O ground-state resonance decay were extracted. The experimental results were compared to Monte Carlo simulations in which the resonance energy and decay mechanism were varied. Results: The measured three-body correlations were well reproduced by the Monte Carlo simulations but were not sensitive to the decay mechanism due to the experimental resolutions. However, the three-body correlations were found to be sensitive to the resonance energy of 26O . A 1 σ upper limit of 53 keV was extracted for the ground-state resonance energy of 26O . Conclusions: Future attempts to measure the three-body correlations from the ground-state decay of 26O will be very challenging due to the need for a precise measurement of the 24O momentum at the reaction point in the target.
Theory of ground state factorization in quantum cooperative systems.
Giampaolo, Salvatore M; Adesso, Gerardo; Illuminati, Fabrizio
2008-05-16
We introduce a general analytic approach to the study of factorization points and factorized ground states in quantum cooperative systems. The method allows us to determine rigorously the existence, location, and exact form of separable ground states in a large variety of, generally nonexactly solvable, spin models belonging to different universality classes. The theory applies to translationally invariant systems, irrespective of spatial dimensionality, and for spin-spin interactions of arbitrary range.
Theory of ground state factorization in quantum cooperative systems.
Giampaolo, Salvatore M; Adesso, Gerardo; Illuminati, Fabrizio
2008-05-16
We introduce a general analytic approach to the study of factorization points and factorized ground states in quantum cooperative systems. The method allows us to determine rigorously the existence, location, and exact form of separable ground states in a large variety of, generally nonexactly solvable, spin models belonging to different universality classes. The theory applies to translationally invariant systems, irrespective of spatial dimensionality, and for spin-spin interactions of arbitrary range. PMID:18518481
Ensemble Theory for Stealthy Hyperuniform Disordered Ground States
NASA Astrophysics Data System (ADS)
Torquato, Salvatore
Disordered hyperuniform many-particle systems have been receiving recent attention because they are distinguishable exotic states of matter poised between a crystal and liquid that are endowed with novel thermodynamic and physical properties. It has been shown numerically that systems of particles interacting with ``stealthy'' bounded, long-ranged pair potentials (similar to Friedel oscillations) have classical ground states that are, counterintuitively, disordered, hyperuniform and highly degenerate. The task of formulating an ensemble theory that yields analytical predictions for the structural characteristics and other properties of stealthy degenerate ground states in d-dimensional Euclidean space is highly nontrivial because the dimensionality of the configuration space depends on the number density and there is a multitude of ways of sampling the ground-state manifold, each with its own probability measure for finding a particular ground-state configuration. A new type of statistical-mechanical theory had to be invented to characterize these exotic states of matter. I report on some initial progress that we have made in this direction. We show that stealthy disordered ground states behave like ''pseudo''-equilibrium hard-sphere systems in Fourier space. Our theoretical predictions for the structure and thermodynamic properties of the stealthy disordered ground states and associated excited states are in excellent agreement with computer simulations across dimensions.
Observation of γ vibrations and alignments built on non-ground-state configurations in 156Dy
NASA Astrophysics Data System (ADS)
Majola, S. N. T.; Hartley, D. J.; Riedinger, L. L.; Sharpey-Schafer, J. F.; Allmond, J. M.; Beausang, C.; Carpenter, M. P.; Chiara, C. J.; Cooper, N.; Curien, D.; Gall, B. J. P.; Garrett, P. E.; Janssens, R. V. F.; Kondev, F. G.; Kulp, W. D.; Lauritsen, T.; McCutchan, E. A.; Miller, D.; Piot, J.; Redon, N.; Riley, M. A.; Simpson, J.; Stefanescu, I.; Werner, V.; Wang, X.; Wood, J. L.; Yu, C.-H.; Zhu, S.
2015-03-01
The exact nature of the lowest Kπ=2+ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the γ degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ bands have been traced past the usual backbending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N =90 nucleus 156Dy , using the 148Nd(12C,4 n ) 156Dy reaction at 65 MeV, observing the resulting γ-ray transitions with the Gammasphere array. The even- and odd-spin members of the Kπ=2+ γ band are observed up to 32+ and 31+, respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ vibration built on the aligned yrast S band are observed up to spins 28+ and 27+. An even-spin positive-parity band, observed up to spin 24+, is a candidate for an aligned S band built on the seniority-zero configuration of the 02+ state at 676 keV. The crossing of this band with the 02+ band is at ℏ ωc=0.28 (1 ) MeV and is consistent with the configuration of the 02+ band not producing any blocking of the monopole pairing.
Experimental study of energy harvesting in UHF band
NASA Astrophysics Data System (ADS)
Bernacki, Ł.; Gozdur, R.; Salamon, N.
2016-04-01
A huge progress of down-sizing technology together with trend of decreasing power consumption and, on the other hand, increasing efficiency of electronics give the opportunity to design and to implement the energy harvesters as main power sources. This paper refers to the energy that can be harvested from electromagnetic field in the unlicensed frequency bands. The paper contains description of the most popular techniques and transducers that can be applied in energy harvesting domain. The overview of current research and commercial solutions was performed for bands in ultra-high frequency range, which are unlicensed and where transmission is not limited by administrative arrangements. During the experiments with Powercast’s receiver, the same bands as sources of electromagnetic field were taken into account. This power source is used for conducting radio-communication process and excess energy could be used for powering the extra electronic circuits. The paper presents elaborated prototype of energy harvesting system and the measurements of power harvested in ultra-high frequency range. The evaluation of RF energy harvesters for powering ultra-low power (ULP) electronic devices was performed based on survey and results of the experiments.
Dissociative recombination of the ground state of N2(+)
NASA Technical Reports Server (NTRS)
Guberman, Steven L.
1991-01-01
Large-scale calculations of the dissociative recombination cross sections and rates for the v = 0 level of the N2(+) ground state are reported, and the important role played by vibrationally excited Rydberg states lying both below and above the v = 0 level of the ion is demonstrated. The large-scale electronic wave function calculations were done using triple zeta plus polarization nuclear-centered-valence Gaussian basis sets. The electronic widths were obtained using smaller wave functions, and the cross sections were calculated on the basis of the multichannel quantum defect theory. The DR rate is calculated at 1.6 x 10 to the -7th x (Te/300) to the -0.37 cu cm/sec for Te in the range of 100 to 1000 K, and is found to be in excellent agreement with prior microwave afterglow experiments but in disagreement with recent merged beam results. It is inferred that the dominant mechanism for DR imparts sufficient energy to the product atoms to allow for escape from the Martian atmosphere.
Hrovat, David; Hou, Gao-Lei; Chen, Bo; Wang, Xue B.; Borden, Weston
2015-11-13
The CO3 radical anion (CO3•–) has been formed by electrospraying carbonate dianion (CO32–) into the gas phase. The negative ion photoelectron (NIPE) spectrum of CO3•– shows that, unlike trimethylenemethane [C(CH2)3], carbontrioxide (CO3) has a singlet ground state. From the NIPE spectrum, the electron affinity of CO3 was determined to be EA = 4.06 ± 0.03 eV, and the singlet-triplet energy difference was found to be ΔEST = - 17.8 ± 0.9 kcal/mol. B3LYP, CCSD(T), and CASPT2 calculations all find that the two lowest triplet states of CO3 are very close in energy, a prediction that is confirmed by the relativemore » intensities of the bands in the NIPE spectrum of CO3•–. The 560 cm-1 vibrational progression, seen in the low energy region of the triplet band, enables the identification of the lowest, Jahn-Teller-distorted, triplet state as 3A1, in which both unpaired electrons reside in σ MOs, rather than 3A2, in which one unpaired electron occupies the b2 σ MO, and the other occupies the b1 π MO.« less
Geometry-independent energy band simulator for radially symmetric diodes
NASA Astrophysics Data System (ADS)
Kirkpatrick, T.; Buonassisi, T.
2016-07-01
In this work, a geometrically independent method to calculate the energy band diagram of radially symmetric diodes is reported. For radially symmetric diodes, the calculation of electron (or hole) energies across the junction can be reduced to a singular spatially dependent variable. Because geometry is not incorporated into the calculation a priori, by reducing the physics to a single spatial variable, energy band calculations can be performed in multiple geometries, simultaneously, for direct comparison to each other. The calculation outlined herein is pseudo-analytical and does not utilize finite element and/or control volume methods. It is, therefore, capable of generating spatially analytic equations for analyzing limiting scenarios of the junction, beneficial for yielding insight into the physics and design criteria of depletion for non-planar semiconducting devices.
Generalized Klein-Gordon models: behavior around the ground state condensate.
Kuetche, Victor K
2014-07-01
In this work, we investigate the balance between the nonlinear and linear interaction energy of an interparticle anharmonic system in the vicinity of the ground state condensate. As a result, we find that the nonlinear interaction energy is very significant in the vicinity of each degree of freedom. We address some potential applications of the findings to miscellaneous areas of interests such as soliton theory, hydrodynamics, solid state physics, ferromagnetic and ferroelectric domain walls, condensed matter physics, and particle physics, among others.
Ground State of the Universe and the Cosmological Constant. A Nonperturbative Analysis.
Husain, Viqar; Qureshi, Babar
2016-02-12
The physical Hamiltonian of a gravity-matter system depends on the choice of time, with the vacuum naturally identified as its ground state. We study the expanding Universe with scalar field in the volume time gauge. We show that the vacuum energy density computed from the resulting Hamiltonian is a nonlinear function of the cosmological constant and time. This result provides a new perspective on the relation between time, the cosmological constant, and vacuum energy.
Generalized Klein-Gordon models: Behavior around the ground state condensate
NASA Astrophysics Data System (ADS)
Kuetche, Victor K.
2014-07-01
In this work, we investigate the balance between the nonlinear and linear interaction energy of an interparticle anharmonic system in the vicinity of the ground state condensate. As a result, we find that the nonlinear interaction energy is very significant in the vicinity of each degree of freedom. We address some potential applications of the findings to miscellaneous areas of interests such as soliton theory, hydrodynamics, solid state physics, ferromagnetic and ferroelectric domain walls, condensed matter physics, and particle physics, among others.
Magnetic ground state of an individual Fe2+ ion in strained semiconductor nanostructure
Smoleński, T.; Kazimierczuk, T.; Kobak, J.; Goryca, M.; Golnik, A.; Kossacki, P.; Pacuski, W.
2016-01-01
Single impurities with nonzero spin and multiple ground states offer a degree of freedom that can be utilized to store the quantum information. However, Fe2+ dopant is known for having a single nondegenerate ground state in the bulk host semiconductors and thus is of little use for spintronic applications. Here we show that the well-established picture of Fe2+ spin configuration can be modified by subjecting the Fe2+ ion to high strain, for example, produced by lattice mismatched epitaxial nanostructures. Our analysis reveals that high strain induces qualitative change in the ion energy spectrum and results in nearly doubly degenerate ground state with spin projection Sz=±2. We provide an experimental proof of this concept using a new system: a strained epitaxial quantum dot containing individual Fe2+ ion. Magnetic character of the Fe2+ ground state in a CdSe/ZnSe dot is revealed in photoluminescence experiments by exploiting a coupling between a confined exciton and the single-iron impurity. We also demonstrate that the Fe2+ spin can be oriented by spin-polarized excitons, which opens a possibility of using it as an optically controllable two-level system free of nuclear spin fluctuations. PMID:26818580
Ground-state properties of small-size nonlinear dynamical lattices
NASA Astrophysics Data System (ADS)
Buonsante, P.; Kevrekidis, P. G.; Penna, V.; Vezzani, A.
2007-01-01
We investigate the ground state of a system of interacting particles in small nonlinear lattices with M⩾3 sites, using as a prototypical example the discrete nonlinear Schrödinger equation that has been recently used extensively in the contexts of nonlinear optics of waveguide arrays and Bose-Einstein condensates in optical lattices. We find that, in the presence of attractive interactions, the dynamical scenario relevant to the ground-state and the lowest-energy modes of such few-site nonlinear lattices reveals a variety of nontrivial features that are absent in the large/infinite lattice limits: the single-pulse solution and the uniform solution are found to coexist in a finite range of the lattice intersite coupling where, depending on the latter, one of them represents the ground state; in addition, the single-pulse mode does not even exist beyond a critical parametric threshold. Finally, the onset of the ground-state (modulational) instability appears to be intimately connected with a nonstandard (“double transcritical”) type of bifurcation that, to the best of our knowledge, has not been reported previously in other physical systems.
Ground states of a prescribed mean curvature equation
NASA Astrophysics Data System (ADS)
del Pino, Manuel; Guerra, Ignacio
We study the existence of radial ground state solutions for the problem -div({∇u√{1+|})=u, u>0 in R, u(x)→0 as |x|→∞, N⩾3, q>1. It is known that this problem has infinitely many ground states when q⩾N+2}/{N-2}, while no solutions exist if q⩽N/N-2. A question raised by Ni and Serrin in [W.-M. Ni, J. Serrin, Existence and non-existence theorems for ground states for quasilinear partial differential equations, Atti Convegni Lincei 77 (1985) 231-257] is whether or not ground state solutions exist for N/N-2ground states with fast decay O(|) as |x|→+∞ provided that q lies below but close enough to the critical exponent {N+2}/{N-2}. These solutions develop a bubble-tower profile as q approaches the critical exponent.
Electronic structure and ground-state properties of Na{sub 2}Po: A first-principles study
Eithiraj, R. D.
2015-06-24
Self-consistent scalar-relativistic band structure calculations have been performed to investigate the electronic structure and ground-state properties of Na{sub 2}Po in cubic antifluorite (anti-CaF{sub 2}-type) structure using the linear muffin-tin orbital in its tight-binding representation (TB-LMTO) method. Ground state properties such as equilibrium lattice constant and bulk modulus were calculated. The results of the electronic structure calculations show that Na{sub 2}Po is direct bandgap semiconductor.
NASA Astrophysics Data System (ADS)
Webster, P. T.; Riordan, N. A.; Liu, S.; Steenbergen, E. H.; Synowicki, R. A.; Zhang, Y.-H.; Johnson, S. R.
2015-12-01
The structural and optical properties of lattice-matched InAs0.911Sb0.089 bulk layers and strain-balanced InAs/InAs1-xSbx (x ˜ 0.1-0.4) superlattices grown on (100)-oriented GaSb substrates by molecular beam epitaxy are examined using X-ray diffraction, spectroscopic ellipsometry, and temperature dependent photoluminescence spectroscopy. The photoluminescence and ellipsometry measurements determine the ground state bandgap energy and the X-ray diffraction measurements determine the layer thickness and mole fraction of the structures studied. Detailed modeling of the X-ray diffraction data is employed to quantify unintentional incorporation of approximately 1% Sb into the InAs layers of the superlattices. A Kronig-Penney model of the superlattice miniband structure is used to analyze the valence band offset between InAs and InAsSb, and hence the InAsSb band edge positions at each mole fraction. The resulting composition dependence of the bandgap energy and band edge positions of InAsSb are described using the bandgap bowing model; the respective low and room temperature bowing parameters for bulk InAsSb are 938 and 750 meV for the bandgap, 558 and 383 meV for the conduction band, and -380 and -367 meV for the valence band.
Webster, P. T.; Riordan, N. A.; Liu, S.; Zhang, Y.-H.; Johnson, S. R.; Steenbergen, E. H.
2015-12-28
The structural and optical properties of lattice-matched InAs{sub 0.911}Sb{sub 0.089} bulk layers and strain-balanced InAs/InAs{sub 1−x}Sb{sub x} (x ∼ 0.1–0.4) superlattices grown on (100)-oriented GaSb substrates by molecular beam epitaxy are examined using X-ray diffraction, spectroscopic ellipsometry, and temperature dependent photoluminescence spectroscopy. The photoluminescence and ellipsometry measurements determine the ground state bandgap energy and the X-ray diffraction measurements determine the layer thickness and mole fraction of the structures studied. Detailed modeling of the X-ray diffraction data is employed to quantify unintentional incorporation of approximately 1% Sb into the InAs layers of the superlattices. A Kronig-Penney model of the superlattice miniband structure is used to analyze the valence band offset between InAs and InAsSb, and hence the InAsSb band edge positions at each mole fraction. The resulting composition dependence of the bandgap energy and band edge positions of InAsSb are described using the bandgap bowing model; the respective low and room temperature bowing parameters for bulk InAsSb are 938 and 750 meV for the bandgap, 558 and 383 meV for the conduction band, and −380 and −367 meV for the valence band.
Does a 5/2 sup + -5/2 sup minus ground-state parity doublet exist in sup 229 Pa
Grafen, V.; Ackermann, B.; Baltzer, H.; Bihn, T.; Guenther, C. ); deBoer, J.; Gollwitzer, N.; Graw, G.; Hertenberger, R.; Kader, H.; Levon, A.; Loesch, A. )
1991-11-01
The 1/2(530) decoupled band in {sup 229}Pa has been identified up to the 19/2{sup {minus}} level in ({ital p},{ital t}) and ({ital p},2{ital n}{gamma}) experiments. It is found that the 3/2{sup {minus}} band head has an excitation energy of 19(10) keV, and can thus not be identified with a 123 keV level observed in the {sup 229}U electron capture decay. This removes the evidence presented earlier for a spin-parity assignment of 5/2{sup +-}5/2{sup {minus}} to a proposed nearly degenerate ground-state doublet in {sup 229}Pa.
Theoretical study of the dissociation energy and the red and violet band systems of CN
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.
1988-01-01
The dissociation energy D0 is determined here for the CN ground-state and radiative lifetimes for the A 2Pi and B 2Sigma(+) states. D0 is found to be 7.65 + or - 0.06 eV, corresponding to Delta Hf (CN) = 105.3 + or - 1.5 kcal/mole. These results are compared with current experimental estimates and with previous theoretical calculations.
Extremal Optimization for Ground States of the Sherrington-Kirkpatrick Spin Glass with Levy Bonds
NASA Astrophysics Data System (ADS)
Boettcher, Stefan
Ground states of Ising spin glasses on fully connected graphs are studied for a broadly distributed bond family. In particular, bonds J distributed according to a Levy distribution P(J) / 1/|J|1+α; |J| > 1; are investigated for a range of powers α. We determine ground state energy density variation with α and their finite-size corrections. We find that the energies attain universally the Parisi-energy of the SK as long as the second moment of P (J) exists (α > 2). They compare favorably with recent one-step replica symmetry breaking predictions well below α = 2. At and just below α = 2, the simulations deviate significantly from theoretical expectations. The finite-size investigation reveals that the corrections exponent ω decays from the putative SK value ωSK = = 2/3 already well above α = 2, at which point it reaches a minimum.
Probing quantum frustrated systems via factorization of the ground state.
Giampaolo, Salvatore M; Adesso, Gerardo; Illuminati, Fabrizio
2010-05-21
The existence of definite orders in frustrated quantum systems is related rigorously to the occurrence of fully factorized ground states below a threshold value of the frustration. Ground-state separability thus provides a natural measure of frustration: strongly frustrated systems are those that cannot accommodate for classical-like solutions. The exact form of the factorized ground states and the critical frustration are determined for various classes of nonexactly solvable spin models with different spatial ranges of the interactions. For weak frustration, the existence of disentangling transitions determines the range of applicability of mean-field descriptions in biological and physical problems such as stochastic gene expression and the stability of long-period modulated structures.
Magnetization ground state and reversal modes of magnetic nanotori
NASA Astrophysics Data System (ADS)
Vojkovic, Smiljan; Nunez, Alvaro S.; Altbir, Dora; Carvalho-Santos, Vagson L.
2016-07-01
In this work, and by means of micromagnetic simulations, we study the magnetic properties of toroidal nanomagnets. The magnetization ground state for different values of the aspect ratio between the toroidal and polar radii of the nanotorus has been obtained. Besides, we have shown that the vortex and the in-plane single domain states can appear as ground states for different ranges of the aspect ratio, while a single domain state with an out-of-plane magnetization is not observed. The hysteresis curves are also obtained, evidencing the existence of two reversal modes depending on the geometry: a vortex mode and a coherent rotation. A comparison between toroidal and cylindrical nanoparticles has been performed evidencing that nanotori can accommodate a vortex as the ground state for smaller volume than cylindrical nanorings.
Ground state and constrained domain walls in Gd /Fe multilayers
NASA Astrophysics Data System (ADS)
Van Aken, Bas B.; Prieto, José L.; Mathur, Neil D.
2005-03-01
The magnetic ground state of antiferromagnetically coupled Gd /Fe multilayers and the evolution of in-plane domain walls is modeled with micromagnetics. The twisted state is characterized by a rapid decrease of the interface angle with increasing magnetic field. We found that for certain ratios MFe:MGd, the twisted state is already present at low fields. However, the magnetic ground state is not only determined by the ratio MFe:MGd but also by the thicknesses of the layers; that is by the total moments of the layer. The dependence of the magnetic ground state is explained by the amount of overlap of the domain walls at the interface. Thicker layers suppress the Fe-aligned and the Gd-aligned state in favor of the twisted state. On the other hand, ultrathin layers exclude the twisted state, since wider domain walls cannot form in these ultrathin layers.
Ground-state geometric quantum computing in superconducting systems
Solinas, P.; Moettoenen, M.
2010-11-15
We present a theoretical proposal for the implementation of geometric quantum computing based on a Hamiltonian which has a doubly degenerate ground state. Thus the system which is steered adiabatically, remains in the ground-state. The proposed physical implementation relies on a superconducting circuit composed of three SQUIDs and two superconducting islands with the charge states encoding the logical states. We obtain a universal set of single-qubit gates and implement a nontrivial two-qubit gate exploiting the mutual inductance between two neighboring circuits, allowing us to realize a fully geometric ground-state quantum computing. The introduced paradigm for the implementation of geometric quantum computing is expected to be robust against environmental effects.
Probing quantum frustrated systems via factorization of the ground state.
Giampaolo, Salvatore M; Adesso, Gerardo; Illuminati, Fabrizio
2010-05-21
The existence of definite orders in frustrated quantum systems is related rigorously to the occurrence of fully factorized ground states below a threshold value of the frustration. Ground-state separability thus provides a natural measure of frustration: strongly frustrated systems are those that cannot accommodate for classical-like solutions. The exact form of the factorized ground states and the critical frustration are determined for various classes of nonexactly solvable spin models with different spatial ranges of the interactions. For weak frustration, the existence of disentangling transitions determines the range of applicability of mean-field descriptions in biological and physical problems such as stochastic gene expression and the stability of long-period modulated structures. PMID:20867055
Toward Triplet Ground State NaLi Molecules
NASA Astrophysics Data System (ADS)
Ebadi, Sepehr; Jamison, Alan; Rvachov, Timur; Jing, Li; Son, Hyungmok; Jiang, Yijun; Zwierlein, Martin; Ketterle, Wolfgang
2016-05-01
The NaLi molecule is expected to have a long lifetime in the triplet ground-state due to its fermionic nature, large rotational constant, and weak spin-orbit coupling. The triplet state has both electric and magnetic dipole moments, affording unique opportunities in quantum simulation and ultracold chemistry. We have mapped the excited state NaLi triplet potential by means of photoassociation spectroscopy. We report on this and our further progress toward the creation of the triplet ground-state molecules using STIRAP. NSF, ARO-MURI, Samsung, NSERC.
Antiferromagnetic ground state with pair-checkerboard order in FeSe
NASA Astrophysics Data System (ADS)
Cao, Hai-Yuan; Chen, Shiyou; Xiang, Hongjun; Gong, Xin-Gao
2015-01-01
A monolayer FeSe thin film grown on SrTiO3(001) (STO) shows the sign of Tc>77 K , which is higher than the Tc record of 56 K for bulk FeAs-based superconductors. However, little is known about the magnetic ground state of FeSe, which should be closely related to its unusual superconductivity. Previous studies presume the collinear stripe antiferromagnetic (AFM) state as the ground state of FeSe, the same as that in FeAs superconductors. Here we find a magnetic order named the "pair-checkerboard AFM" as the magnetic ground state of tetragonal FeSe. The pair-checkerboard order results from the interplay between the nearest-, next-nearest, and unnegligible next-next-nearest neighbor magnetic exchange couplings of Fe atoms. The monolayer FeSe in pair-checkerboard order shows an unexpected insulating behavior with a Dirac-cone-like band structure related to the specific orbital order of the dx z and dy z characters of Fe atoms, which could explain the recently observed insulator-superconductor transition. The present results cast insights on the magnetic ordering in FeSe monolayer and its derived superconductors.
High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb
NASA Astrophysics Data System (ADS)
Sirohi, Anshu; Singh, Chandan K.; Thakur, Gohil S.; Saha, Preetha; Gayen, Sirshendu; Gaurav, Abhishek; Jyotsna, Shubhra; Haque, Zeba; Gupta, L. C.; Kabir, Mukul; Ganguli, Ashok K.; Sheet, Goutam
2016-06-01
CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (˜47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane are strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.
Preparing ground states of quantum many-body systems on a quantum computer
NASA Astrophysics Data System (ADS)
Poulin, David
2009-03-01
The simulation of quantum many-body systems is a notoriously hard problem in condensed matter physics, but it could easily be handled by a quantum computer [4,1]. There is however one catch: while a quantum computer can naturally implement the dynamics of a quantum system --- i.e. solve Schr"odinger's equation --- there was until now no general method to initialize the computer in a low-energy state of the simulated system. We present a quantum algorithm [5] that can prepare the ground state and thermal states of a quantum many-body system in a time proportional to the square-root of its Hilbert space dimension. This is the same scaling as required by the best known algorithm to prepare the ground state of a classical many-body system on a quantum computer [3,2]. This provides strong evidence that for a quantum computer, preparing the ground state of a quantum system is in the worst case no more difficult than preparing the ground state of a classical system. 1 D. Aharonov and A. Ta-Shma, Adiabatic quantum state generation and statistical zero knowledge, Proc. 35th Annual ACM Symp. on Theo. Comp., (2003), p. 20. F. Barahona, On the computational complexity of ising spin glass models, J. Phys. A. Math. Gen., 15 (1982), p. 3241. C. H. Bennett, E. Bernstein, G. Brassard, and U. Vazirani, Strengths and weaknessess of quantum computing, SIAM J. Comput., 26 (1997), pp. 1510--1523, quant-ph/9701001. S. Lloyd, Universal quantum simulators, Science, 273 (1996), pp. 1073--1078. D. Poulin and P. Wocjan, Preparing ground states of quantum many-body systems on a quantum computer, 2008, arXiv:0809.2705.
Orbital Ordering and Frustration of p-Band Mott Insulators
Wu Congjun
2008-05-23
We investigate the general structure of orbital exchange physics in Mott-insulating states of p-orbital systems in optical lattices. Orbital orders occur in both the triangular and kagome lattices. In contrast, orbital exchange in the honeycomb lattice is frustrated as described by a novel quantum 120 deg. model. Its classical ground states are mapped into configurations of the fully packed loop model with an extra U(1) rotation degree of freedom. Quantum orbital fluctuations select a six-site plaquette ground state ordering pattern in the semiclassical limit from the 'order from disorder' mechanism. This effect arises from the appearance of a zero energy flat band of orbital excitations.
Ground state phase transition in the Nilsson mean-field plus standard pairing model
NASA Astrophysics Data System (ADS)
Guan, Xin; Xu, Haocheng; Zhang, Yu; Pan, Feng; Draayer, Jerry P.
2016-08-01
The ground state phase transition in Nd, Sm, and Gd isotopes is investigated by using the Nilsson mean-field plus standard pairing model based on the exact solutions obtained from the extended Heine-Stieltjes correspondence. The results of the model calculations successfully reproduce the critical phenomena observed experimentally in the odd-even mass differences, odd-even differences of two-neutron separation energy, and the α -decay and double β--decay energies of these isotopes. Since the odd-even effects are the most important signatures of pairing interactions in nuclei, the model calculations yield microscopic insight into the nature of the ground state phase transition manifested by the standard pairing interaction.
Karolewski, Andreas; Kronik, Leeor; Kümmel, Stephan
2013-05-28
Optimally tuned range separated hybrid functionals are a new class of implicitly defined functionals. Their important new aspect is that the range separation parameter in these functionals is determined individually for each system by iteratively tuning it until a fundamental, non-empirical condition is fulfilled. Such functionals have been demonstrated to be extremely successful in predicting electronic excitations. In this paper, we explore the use of the tuning approach for predicting ground state properties. This sheds light on one of its downsides - the violation of size consistency. By analyzing diatomic molecules, we reveal size consistency errors up to several electron volts and find that binding energies cannot be predicted reliably. Further consequences of the consistent ground-state use of the tuning approach are potential energy surfaces that are qualitatively in error and an incorrect prediction of spin states. We discuss these failures, their origins, and possibilities for overcoming them.
Ground states of bilayered and extended t-J-U models
NASA Astrophysics Data System (ADS)
Voo, Khee-Kyun
2015-09-01
The ground states of bilayered and extended t-J-U models are investigated with renormalized mean field theory. The trial wave functions are Gutzwiller projected Hartree-Fock states, and the site double occupancies are variational parameters. It is found that a spontaneous interlayer phase separation (PS) may arise in bilayers. In electron-hole doping asymmetric systems, the propensity for PS is stronger in electron doped bands. Via a PS, superconductivity can survive to lower doping densities, and antiferromagnetism in electron doped systems may survive to higher doping densities. The result is related to the superconducting cuprates.
NASA Astrophysics Data System (ADS)
Demyanova, A. S.; Danilov, A. N.; Dmitriev, S. V.; Ogloblin, A. A.; Belyaeva, T. L.; Goncharov, S. A.; Gurov, Yu. B.; Maslov, V. A.; Sobolev, Yu. G.; Trzaska, W.; Heikkinen, P.; Julin, R.; Khlebnikov, S. V.; Tyurin, G. P.; Burtebaev, N.; Zholdybayev, T.
2015-06-01
Differential cross-sections of the 11B + α inelastic scattering at E(α) = 65 leading to the most of the known 11B states at the excitation energies up to 14 MeV were measured. The data analysis was done by DWBA and in some cases by the modified diffraction model allowing determining the radii of the excited states. The radii of the states with excitation energies less than ~ 7 MeV with the accuracy not less than 0.1-0.15 fm coincide with the radius of the ground state. This result is consistent with the traditional view of the shell structure of the low-lying states in 11B. Most of the observed high-energy excited states are distributed among four rotational bands. The moments of inertia of band states are close to the moment of inertia of the Hoyle state of 12C. The calculated radii, related to these bands, are 0.7 - 1.0 fm larger than the radius of the ground state, and are close to the radius of the Hoyle state. These results are in agreement with existing predictions about various cluster structure of 11B at high excitation energies. The state with the excitation energy 12.56 MeV, Iπ = 1/2+, T = 1/2 and the root mean square radius R ~ 6 fm predicted in the frame of the alpha condensate hypothesis was not found. The observed level at 12.6 MeV really has T = 1/2, probably, Iπ = 3/2+ and the radius close to that of the ground state.
Cold collisions of ground-state calcium atoms in a laser field: A theoretical study
Bussery-Honvault, Beatrice; Launay, Jean-Michel; Moszynski, Robert
2003-09-01
State-of-the-art ab initio techniques have been applied to compute the potential-energy curves for the ground X {sup 1}{sigma}{sub g}{sup +} and excited {sup 1}{pi}{sub g}(4s3d) states of the calcium dimer in the Born-Oppenheimer approximation. The weakly bound ground state was calculated by symmetry-adapted perturbation theory, while the strongly bound excited state was computed using a combination of the linear-response theory within the coupled-cluster singles and doubles framework for the core-valence electronic correlation and of the full configuration interaction for the valence-valence correlation. The ground-state potential has been corrected by considering the relativistic terms resulting from the first-order many-electron Breit theory, and the retardation corrections. The magnetic electronic transition dipole moment governing the {sup 1}{pi}{sub g}(leftarrow){sup 1}{sigma}{sub g}{sup +} transitions has been obtained as the first residue of the polarization propagator computed with the coupled-cluster method restricted to single and double excitations. The computed energies and transition moments have been analytically fitted and used in the dynamical calculations of the rovibrational energy levels, ground-state scattering length, photoassociation intensities at ultralow temperatures, and spontaneous emission coefficients from the {sup 1}{pi}{sub g}(4s3d) to the X {sup 1}{sigma}{sub g}{sup +} state. The spectroscopic constants of the theoretical ground-state potential are in a good agreement with the experimental values derived from the Fourier-transform spectra [O. Allard et al., Eur. Phys. J. D (to be published)]. The theoretical s-wave scattering length for the ground state is a=44 bohrs, suggesting that it should be possible to obtain a stable Bose-Einstein condensate of calcium atoms. Finally, the computed photoassociation intensities and spontaneous emission coefficients suggest that it should be possible to obtain cold calcium molecules by
Tuning ground states and excitations in complex electronic materials
Bishop, A.R.
1996-09-01
Modern electronic materials are characterized by a great variety of broken-symmetry ground states and excitations. Their control requires understanding and tuning underlying driving forces of spin-charge-lattice coupling, critical to macroscopic properties and applications. We report representative model calculations which demonstrate some of the richness of the phenomena and the challenges for successful microscopic modeling.
Diagrammatic perturbation theory applied to the ground state of the water molecule
NASA Technical Reports Server (NTRS)
Silver, D. M.; Wilson, S.
1977-01-01
The diagrammatic many-body perturbation theory is applied to the ground state of the water molecule within the algebraic approximation. Using four different basis sets, the total energy, the equilibrium OH bond length, and the equilibrium HOH bond angle are examined. The latter is found to be a particularly sensitive test of the convergence of perturbation expansions. Certain third-order results, which incorporate all two-, three-, and four-body effects, show evidence of good convergence properties.
A simple, radially correlated ground state wavefunction for two electron atoms.
NASA Technical Reports Server (NTRS)
Altick, P. L.
1972-01-01
A one parameter function is presented as an approximation to the ground state wavefunction of the two electron radial hamiltonian. The parameter may be fixed by a nonvariational criterion. The resulting expectation value of the radial hamiltonian differs from its exact eigenvalue by about 2 parts in 3000 for helium while the 'local energy' never differs by more than 10% from the exact value over the entire r1-r2 plane. The cases Z = 1 and Z = 3 are also investigated.
Dayou, Fabrice; Duflot, Denis; Rivero-Santamaría, Alejandro; Monnerville, Maurice
2013-11-28
We report the first global potential energy surface (PES) for the X{sup 2}A{sup ′} ground electronic state of the Si({sup 3}P) + OH(X{sup 2}Π) → SiO(X{sup 1}Σ{sub g}{sup +}) + H({sup 2}S) reaction. The PES is based on a large number of ab initio energies obtained from multireference configuration interaction calculations plus Davidson correction (MRCI+Q) using basis sets of quadruple zeta quality. Corrections were applied to the ab initio energies in the reactant channel allowing a proper description of long-range interactions between Si({sup 3}P) and OH(X{sup 2}Π). An analytical representation of the global PES has been developed by means of the reproducing kernel Hilbert space method. The reaction is found barrierless. Two minima, corresponding to the SiOH and HSiO isomers, and six saddle points, among which the isomerization transition state, have been characterized on the PES. The vibrational spectra of the SiOH/HSiO radicals have been computed from second-order perturbation theory and quantum dynamics methods. The structural, energetic, and spectroscopic properties of the two isomers are in good agreement with experimental data and previous high quality calculations.
Energy band diagram of device-grade silicon nanocrystals.
Macias-Montero, M; Askari, S; Mitra, S; Rocks, C; Ni, C; Svrcek, V; Connor, P A; Maguire, P; Irvine, J T S; Mariotti, D
2016-03-28
Device grade silicon nanocrystals (NCs) are synthesized using an atmospheric-pressure plasma technique. The Si NCs have a small and well defined size of about 2.3 nm. The synthesis system allows for the direct creation of thin films, enabling a range of measurements to be performed and easy implementation of this material in different devices. The chemical stability of the Si NCs is evaluated, showing relatively long-term durability thanks to hydrogen surface terminations. Optical and electrical characterization techniques, including Kelvin probe, ultraviolet photoemission spectroscopy and Mott-Schottky analysis, are employed to determine the energy band diagram of the Si NCs. PMID:26939617
NASA Astrophysics Data System (ADS)
Kakehashi, Yoshiro; Chandra, Sumal
2016-08-01
The ground-state properties of iron-group transition metals from Sc to Cu have been investigated on the basis of the first-principles momentum dependent local ansatz (MLA) theory. Correlation energy gain is found to show large values for Mn and Fe: 0.090 Ry (Mn) and 0.094 Ry (Fe). The Hund-rule coupling energies are found to be 3000 K (Fe), 1400 K (Co), and 300 K (Ni). It is suggested that these values can resolve the inconsistency in magnetic energy between the density functional theory and the first-principles dynamical coherent potential approximation theory at finite temperatures. Charge fluctuations are shown to be suppressed by the intra-orbital correlations and inter-orbital charge-charge correlations, so that they show nearly constant values from V to Fe: 1.57 (V and Cr), 1.52 (Mn), and 1.44 (Fe), which are roughly twice as large as those obtained by the d band model. The amplitudes of local moments are enhanced by the intra-orbital and inter-orbital spin-spin correlations and show large values for Mn and Fe: 2.87 (Mn) and 2.58 (Fe). These values are in good agreement with the experimental values estimated from the effective Bohr magneton number and the inner core photoemission data.
Lowering of ground state induced by core-shell structure in strontium titanate
NASA Astrophysics Data System (ADS)
Kiat, J. M.; Hehlen, B.; Anoufa, M.; Bogicevic, C.; Curfs, C.; Boyer, B.; Al-Sabbagh, M.; Porcher, F.; Al-Zein, A.
2016-04-01
A new ground state of textbook compound strontium titanate (SrTi O3) is obtained by inducing a specific core-shell structure of the particles. Using a combination of high energy synchrotron and neutron diffraction, we demonstrate a lowering of the ferroelastic ground state towards a new antiferrodistortive phase, accompanied with strong shifts of the critical temperature. This new phase is discussed within the Landau theory and compared with the situation in thin films and during pressure experiments. The crucial competition between particle shape anisotropy, surface tension, and shear strain is analyzed. Inducing a specific core-shell structure is therefore an easy way to tailor structural properties and to stabilize new phases that cannot exist in bulk material, just like film deposition on a substrate.
The theoretical study of the ground-state polar chromium-alkali-metal-atom molecules
NASA Astrophysics Data System (ADS)
Deng, Lijuan; Gou, Dezhi; Chai, Junshuai
2016-04-01
Potential energy curves and permanent dipole moments of the 6Σ+ and 8Σ+ ground state of CrX (X = Li, Na, K, Rb and Cs) are calculated by employing the complete active space self-consistent field (CASSCF) and multi-reference configuration interaction (MRCI) methods. The spectroscopic constants for the 6Σ+ and 8Σ+ ground state of these molecules are calculated. Moreover, CrK, CrRb and CrCs molecules with large values of permanent dipole moment (CrK: 5.553 D, CrRb: 6.341 D and CrCs: 6.731 D) at the equilibrium bond distance are potentially interesting candidates for ultracold anisotropic long-range dipole-dipole interactions and many-body physics studies.
Rayleigh approximation to ground state of the Bose and Coulomb glasses
Ryan, S. D.; Mityushev, V.; Vinokur, V. M.; Berlyand, L.
2015-01-16
Glasses are rigid systems in which competing interactions prevent simultaneous minimization of local energies. This leads to frustration and highly degenerate ground states the nature and properties of which are still far from being thoroughly understood. We report an analytical approach based on the method of functional equations that allows us to construct the Rayleigh approximation to the ground state of a two-dimensional (2D) random Coulomb system with logarithmic interactions. We realize a model for 2D Coulomb glass as a cylindrical type II superconductor containing randomly located columnar defects (CD) which trap superconducting vortices induced by applied magnetic field. Ourmore » findings break ground for analytical studies of glassy systems, marking an important step towards understanding their properties.« less
Role of the helium ground state in (e,3e) processes
Ancarani, L.U.; Montagnese, T.; Dal Cappello, C.
2004-07-01
Absolute (e,3e) measurements on helium, at high incident energy, have been recently reproduced by a calculation in the first Born approximation [Phys. Rev. Lett. 91, 73201 (2003)]. The theoretical model is based on the product of three Coulomb waves for the final state and the use of Pluvinage wave function for the initial helium ground state. The authors suggest that the good agreement obtained is strongly related to the quality of the initial state, in particular to the fact that it is diagonal in all Coulomb interactions. In this paper, we show that this conclusion is not correct. We construct three other helium ground states to demonstrate that diagonalizing the Hamiltonian is not the deciding factor in obtaining agreement with the absolute experimental data.
Rayleigh approximation to ground state of the Bose and Coulomb glasses
Ryan, S. D.; Mityushev, V.; Vinokur, V. M.; Berlyand, L.
2015-01-16
Glasses are rigid systems in which competing interactions prevent simultaneous minimization of local energies. This leads to frustration and highly degenerate ground states the nature and properties of which are still far from being thoroughly understood. We report an analytical approach based on the method of functional equations that allows us to construct the Rayleigh approximation to the ground state of a two-dimensional (2D) random Coulomb system with logarithmic interactions. We realize a model for 2D Coulomb glass as a cylindrical type II superconductor containing randomly located columnar defects (CD) which trap superconducting vortices induced by applied magnetic field. Our findings break ground for analytical studies of glassy systems, marking an important step towards understanding their properties.
Ground states for irregular and indefinite superlinear Schrödinger equations
NASA Astrophysics Data System (ADS)
Ackermann, Nils; Chagoya, Julián
2016-11-01
We consider the existence of a ground state for the subcritical stationary semilinear Schrödinger equation - Δu + u = a (x) | u| p - 2 u in H1, where a ∈L∞ (RN) may change sign. Our focus is on the case where loss of compactness occurs at the ground state energy. By providing a new variant of the Splitting Lemma we do not need to assume the existence of a limit problem at infinity, be it in the form of a pointwise limit for a as | x | → ∞ or of asymptotic periodicity. That is, our problem may be irregular at infinity. In addition, we allow a to change sign near infinity, a case that has never been treated before.
Creation of Ultracold Sr2 Molecules in the Electronic Ground State
NASA Astrophysics Data System (ADS)
Stellmer, Simon; Pasquiou, Benjamin; Grimm, Rudolf; Schreck, Florian
2012-09-01
We report on the creation of ultracold Sr284 molecules in the electronic ground state. The molecules are formed from atom pairs on sites of an optical lattice using stimulated Raman adiabatic passage (STIRAP). We achieve a transfer efficiency of 30% and obtain 4×104 molecules with full control over the external and internal quantum state. STIRAP is performed near the narrow S01-P13 intercombination transition, using a vibrational level of the 1(0u+) potential as an intermediate state. In preparation of our molecule association scheme, we have determined the binding energies of the last vibrational levels of the 1(0u+), 1(1u) excited-state and the XΣg+1 ground-state potentials. Our work overcomes the previous limitation of STIRAP schemes to systems with magnetic Feshbach resonances, thereby establishing a route that is applicable to many systems beyond alkali-metal dimers.
Structural Studies of Metastable and Ground State Vortex Lattice Domains in MgB2
NASA Astrophysics Data System (ADS)
de Waard, E. R.; Kuhn, S. J.; Rastovski, C.; Eskildsen, M. R.; Leishman, A.; Dewhurst, C. D.; Debeer-Schmitt, L.; Littrell, K.; Karpinski, J.; Zhigadlo, N. D.
2015-03-01
Small-angle neutron scattering (SANS) studies of the vortex lattice (VL) in the type-II superconductor MgB2 have revealed an unprecedented degree of metastability that is demonstrably not due to vortex pinning, [C. Rastovski et al . , Phys. Rev. Lett. 111, 107002 (2013)]. Application of an AC magnetic field to drive the VL to the ground state revealed a two-step power law behavior, indicating a slow nucleation of ground state domains followed by a faster growth. The dependence on the number of applied AC cycles is reminiscent of jamming of soft, frictionless spheres. Here, we report on detailed structural studies of both metastable and ground state VL domains. These include measurements of VL correlation lengths as well as spatially resolved SANS measurements showing the VL domain distribution within the MgB2 single crystal. We discuss these results and how they may help to resolve the mechanism responsible for stabilizing the metastable VL phases. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Award DE-FG02-10ER46783.
Loading Bose-Einstein-condensed atoms into the ground state of an optical lattice
Julienne, P. S.; Williams, C. J.; Band, Y. B.; Trippenbach, Marek
2005-11-15
We optimize the turning on of a one-dimensional optical potential, V{sub L}(x,t)=S(t)V{sub 0} cos{sup 2}(kx) to obtain the optimal turn-on function S(t) so as to load a Bose-Einstein condensate into the ground state of the optical lattice of depth V{sub 0}. Specifically, we minimize interband excitations at the end of the turn-on of the optical potential at the final ramp time t{sub r}, where S(t{sub r})=1, given that S(0)=0. Detailed numerical calculations confirm that a simple unit cell model is an excellent approximation when the turn-on time t{sub r} is long compared with the inverse of the band excitation frequency and short in comparison with nonlinear time ({Dirac_h}/2{pi})/{mu} where {mu} is the chemical potential of the condensate. We demonstrate using the Gross-Pitaevskii equation with an optimal turn-on function S(t) that the ground state of the optical lattice can be loaded with no significant excitation even for times t{sub r} on the order of the inverse band excitation frequency.
Ground-state properties of trapped Bose-Fermi mixtures: Role of exchange correlation
Albus, Alexander P.; Wilkens, Martin; Illuminati, Fabrizio
2003-06-01
We introduce density-functional theory for inhomogeneous Bose-Fermi mixtures, derive the associated Kohn-Sham equations, and determine the exchange-correlation energy in local-density approximation. We solve numerically the Kohn-Sham system, and determine the boson and fermion density distributions and the ground-state energy of a trapped, dilute mixture beyond mean-field approximation. The importance of the corrections due to exchange correlation is discussed by a comparison with current experiments; in particular, we investigate the effect of the repulsive potential-energy contribution due to exchange correlation on the stability of the mixture against collapse.
Energy band diagram of device-grade silicon nanocrystals
NASA Astrophysics Data System (ADS)
Macias-Montero, M.; Askari, S.; Mitra, S.; Rocks, C.; Ni, C.; Svrcek, V.; Connor, P. A.; Maguire, P.; Irvine, J. T. S.; Mariotti, D.
2016-03-01
Device grade silicon nanocrystals (NCs) are synthesized using an atmospheric-pressure plasma technique. The Si NCs have a small and well defined size of about 2.3 nm. The synthesis system allows for the direct creation of thin films, enabling a range of measurements to be performed and easy implementation of this material in different devices. The chemical stability of the Si NCs is evaluated, showing relatively long-term durability thanks to hydrogen surface terminations. Optical and electrical characterization techniques, including Kelvin probe, ultraviolet photoemission spectroscopy and Mott-Schottky analysis, are employed to determine the energy band diagram of the Si NCs.Device grade silicon nanocrystals (NCs) are synthesized using an atmospheric-pressure plasma technique. The Si NCs have a small and well defined size of about 2.3 nm. The synthesis system allows for the direct creation of thin films, enabling a range of measurements to be performed and easy implementation of this material in different devices. The chemical stability of the Si NCs is evaluated, showing relatively long-term durability thanks to hydrogen surface terminations. Optical and electrical characterization techniques, including Kelvin probe, ultraviolet photoemission spectroscopy and Mott-Schottky analysis, are employed to determine the energy band diagram of the Si NCs. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07705b
NASA Astrophysics Data System (ADS)
Paul, Bijan Kumar; Guchhait, Nikhil
2013-02-01
Density functional theory based computational study has been performed to characterize intramolecular hydrogen bonding (IMHB) interaction in a series of salicylic acid derivatives varying in chlorine substitution on the benzene ring. The molecular systems studied are salicylic acid, 5-chlorosalicylic acid, 3,5-dichlorosalicylic acid and 3,5,6-tricholorosalicylic acid. Major emphasis is rendered on the analysis of IMHB interaction by calculation of electron density ρ(r) and Laplacian ∇2ρ(r) at the bond critical point using atoms-in-molecule theory. Topological features, energy densities based on ρ(r) through perturbing the intramolecular H-bond distances suggest that at equilibrium geometry the IMHB interaction develops certain characteristics typical of covalent interaction. The interplay between aromaticity and resonance-assisted hydrogen bonding (RAHB) is discussed using both geometrical and magnetic criteria as the descriptors of aromaticity. The optimized geometry features, molecular electrostatic potential map analysis are also found to produce a consensus view in relation with the formation of RAHB in these systems.
Broad band spectral energy distribution studies of Fermi bright blazars
NASA Astrophysics Data System (ADS)
Monte, C.; Giommi, P.; Cavazzuti, E.; Gasparrini, D.; Rainò, S.; Fuhrmann, L.; Angelakis, E.; Villata, M.; Raiteri, C. M.; Perri, M.; Richards, J.
2011-02-01
The Fermi Gamma-ray Space Telescope was successfully launched on June 11, 2008 and has already opened a new era for gamma-ray astronomy. The Large Area Telescope (LAT), the main instrument on board Fermi, presents a significant improvement in sensitivity over its predecessor EGRET, due to its large field of view and effective area, combined with its excellent timing capabilities. The preliminary results of the Spectral Energy Distribution Analysis performed on a sample of bright blazars are presented. For this study, the data from the first three months of data collection of Fermi have been used. The analysis is extended down to radio, mm, near-IR, optical, UV and X-ray bands and up to TeV energies based on unprecedented sample of simultaneous multi-wavelength observations by GASP-WEBT.
Terahertz spectroscopy of ground state HD18O
NASA Astrophysics Data System (ADS)
Yu, Shanshan; Pearson, John C.; Drouin, Brian J.; Miller, Charles E.; Kobayashi, Kaori; Matsushima, Fusakazu
2016-10-01
Terahertz absorption spectroscopy was employed to measure the ground state pure rotational transitions of the water isotopologue HD18O . A total of 105 pure rotational transitions were observed in the 0.5-5.0 THz region with ∼ 100 kHz accuracy for the first time. The observed positions were fit to experimental accuracy using the Euler series expansion of the asymmetric-top Hamiltonian together with the literature Microwave, Far-IR and IR data in the ground state and ν2 . The new measurements and predictions reported here support the analysis of astronomical observations by high-resolution spectroscopic telescopes such as SOFIA and ALMA where laboratory rest frequencies with uncertainties of 1 MHz or less are required for proper analysis of velocity resolved astrophysical data.
Coherent Control of Ground State NaK Molecules
NASA Astrophysics Data System (ADS)
Yan, Zoe; Park, Jee Woo; Loh, Huanqian; Will, Sebastian; Zwierlein, Martin
2016-05-01
Ultracold dipolar molecules exhibit anisotropic, tunable, long-range interactions, making them attractive for the study of novel states of matter and quantum information processing. We demonstrate the creation and control of 23 Na40 K molecules in their rovibronic and hyperfine ground state. By applying microwaves, we drive coherent Rabi oscillations of spin-polarized molecules between the rotational ground state (J=0) and J=1. The control afforded by microwave manipulation allows us to pursue engineered dipolar interactions via microwave dressing. By driving a two-photon transition, we are also able to observe Ramsey fringes between different J=0 hyperfine states, with coherence times as long as 0.5s. The realization of long coherence times between different molecular states is crucial for applications in quantum information processing. NSF, AFOSR- MURI, Alfred P. Sloan Foundation, DARPA-OLE
Ground states of trapped spin-1 condensates in magnetic field
Matuszewski, Michal
2010-11-15
We consider a spin-1 Bose-Einstein condensate trapped in a harmonic potential under the influence of a homogeneous magnetic field. We investigate spatial and spin structure of the mean-field ground states under constraints on the number of atoms and the total magnetization. We show that the trapping potential can make the antiferromagnetic condensate separate into three distinct phases and ferromagnetic condensate into two distinct phases. In the ferromagnetic case, the magnetization is located in the center of the harmonic trap, while in the antiferromagnetic case magnetized phases appear in the outer regions. We describe how the transition from the Thomas-Fermi regime to the single-mode approximation regime with decreasing number of atoms results in the disappearance of the domains. We suggest that the ground states can be created in experiment by adiabatically changing the magnetic-field strength.
Nuclear quadrupole moment of the {sup 99}Tc ground state
Errico, Leonardo; Darriba, German; Renteria, Mario; Tang Zhengning; Emmerich, Heike; Cottenier, Stefaan
2008-05-15
By combining first-principles calculations and existing nuclear magnetic resonance (NMR) experiments, we determine the quadrupole moment of the 9/2{sup +} ground state of {sup 99}Tc to be (-)0.14(3)b. This confirms the value of -0.129(20)b, which is currently believed to be the most reliable experimental determination, and disagrees with two earlier experimental values. We supply ab initio calculated electric-field gradients for Tc in YTc{sub 2} and ZrTc{sub 2}. If this calculated information would be combined with yet to be performed Tc-NMR experiments in these compounds, the error bar on the {sup 99}Tc ground state quadrupole moment could be further reduced.
Kac-Moody symmetries of critical ground states
NASA Astrophysics Data System (ADS)
Kondev, Jané; Henley, Christopher L.
1996-02-01
The symmetries of critical ground states of two-dimensional lattice models are investigated. We show how mapping a critical ground state to a model of a rough interface can be used to identify the chiral symmetry algebra of the conformal field theory that describes its scaling limit. This is demonstrated in the case of the six-vertex model, the three-coloring model on the honeycomb lattice, and the four-coloring model on the square lattice. These models are critical and they are described in the continuum by conformal field theories whose symmetry algebras are the su(2) k=1 , su(3) k=1 , and the su(4) k=1 Kac-Moody algebra, respectively. Our approach is based on the Frenkel-Kac-Segal vertex operator construction of level-one Kac-Moody algebras.
The valence-fluctuating ground state of plutonium
Janoschek, Marc; Das, Pinaki; Chakrabarti, Bismayan; Abernathy, Douglas L.; Lumsden, Mark D.; Lawrence, John M.; Thompson, Joe D.; Lander, Gerard H.; Mitchell, Jeremy N.; Richmond, Scott; Ramos, Mike; Trouw, Frans; Zhu, Jian-Xin; Haule, Kristjan; Kotliar, Gabriel; Bauer, Eric D.
2015-01-01
A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise because of the competition of localized and itinerant electronic degrees of freedom. Although the respective limits of well-localized or entirely itinerant ground states are well understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and nonbonding configurations. Our study reveals that the ground state of plutonium is governed by valence fluctuations, that is, a quantum mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium’s magnetism but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials. PMID:26601219
Cluster expansion for ground states of local Hamiltonians
NASA Astrophysics Data System (ADS)
Bastianello, Alvise; Sotiriadis, Spyros
2016-08-01
A central problem in many-body quantum physics is the determination of the ground state of a thermodynamically large physical system. We construct a cluster expansion for ground states of local Hamiltonians, which naturally incorporates physical requirements inherited by locality as conditions on its cluster amplitudes. Applying a diagrammatic technique we derive the relation of these amplitudes to thermodynamic quantities and local observables. Moreover we derive a set of functional equations that determine the cluster amplitudes for a general Hamiltonian, verify the consistency with perturbation theory and discuss non-perturbative approaches. Lastly we verify the persistence of locality features of the cluster expansion under unitary evolution with a local Hamiltonian and provide applications to out-of-equilibrium problems: a simplified proof of equilibration to the GGE and a cumulant expansion for the statistics of work, for an interacting-to-free quantum quench.
The valence-fluctuating ground state of plutonium
Janoschek, Marc; Das, Pinaki; Chakrabarti, Bismayan; Abernathy, Douglas L.; Lumsden, Mark D.; Lawrence, John M.; Thompson, Joe D.; Lander, Gerard H.; Mitchell, Jeremy N.; Richmond, Scott; Ramos, Mike; Trouw, Frans; Zhu, Jian -Xin; Haule, Kristjan; Kotliar, Gabriel; Bauer, Eric D.
2015-07-10
A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise because of the competition of localized and itinerant electronic degrees of freedom. Although the respective limits of well-localized or entirely itinerant ground states are well understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and nonbonding configurations. In addition, our study reveals that the ground state of plutonium is governed by valence fluctuations, that is, a quantum mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium’s magnetism but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials.
A ground state depleted laser in neodymium doped yttrium orthosilicate
Beach, R.; Albrecht, G.; Solarz, R.; Krupke, W.; Comaskey, B.; Mitchell, S.; Brandle, C.; Berkstresser, G.
1990-01-16
A ground state depleted (GSD){sup 1,2} laser has been demonstrated in the form of a Q-switched oscillator operating at 912 nm. Using Nd{sup 3+} as the active ion and Y{sub 2}SiO{sub 5} as the host material, the laser transition is from the lowest lying stark level of the Nd{sup 3t}F{sub 3/2} level to a stark level 355 cm{sup {minus}1} above the lowest lying one in the {sup 4}I{sub 9/2} manifold. The necessity of depleting the ground {sup 4}I{sub 9/2} manifold is evident for this level scheme as transparency requires a 10% inversion. To achieve the high excitation levels required for the efficient operation of this laser, bleach wave pumping using an alexandrite laser at 745 nm has been employed. The existence of a large absorption feature at 810 nm also allows for the possibility of AlGaAs laser diode pumping. Using KNbO{sub 3}, noncritical phase matching is possible at 140{degree}C using d{sub 32} and has been demonstrated. The results of Q-switched laser performance and harmonic generation in KNbO{sub 3} will be presented. Orthosilicate can be grown in large boules of excellent optical quality using a Czochralski technique. Because of the relatively small 912 nm emission cross section of 2-3 {times} 10{sup {minus}20} cm{sup 2} (orientation dependent) fluences of 10-20 J/cm{sup 2} must be circulated in the laser cavity for the efficient extraction of stored energy. This necessitates very aggressive laser damage thresholds. Results from the Reptile laser damage facility at Lawrence Livermore National Laboratory (LLNL) will be presented showing Y{sub 2}SiO{sub 5} bulk and AR sol-gel coated surface damage thresholds of greater than 40 J/cm{sup 2} for 10 nsec, 10 Hz, 1.06 {mu} pulses. 16 refs., 18 figs., 6 tabs.
Ultracold triplet molecules in the rovibrational ground state.
Lang, F; Winkler, K; Strauss, C; Grimm, R; Denschlag, J Hecker
2008-09-26
We report here on the production of an ultracold gas of tightly bound Rb2 triplet molecules in the rovibrational ground state, close to quantum degeneracy. This is achieved by optically transferring weakly bound Rb2 molecules to the absolute lowest level of the ground triplet potential with a transfer efficiency of about 90%. The transfer takes place in a 3D optical lattice which traps a sizeable fraction of the tightly bound molecules with a lifetime exceeding 200 ms. PMID:18851446
Electronic and ground state properties of ThTe
NASA Astrophysics Data System (ADS)
Bhardwaj, Purvee; Singh, Sadhna
2016-05-01
The electronic properties of ThTe in cesium chloride (CsCl, B2) structure are investigated in the present paper. To study the ground state properties of thorium chalcogenide, the first principle calculations have been calculated. The bulk properties, including lattice constant, bulk modulus and its pressure derivative are obtained. The calculated equilibrium structural parameters are in good agreement with the available experimental and theoretical results.
Measured atomic ground-state polarizabilities of 35 metallic elements
NASA Astrophysics Data System (ADS)
Ma, Lei; Indergaard, John; Zhang, Baiqian; Larkin, Ilia; Moro, Ramiro; de Heer, Walt A.
2015-01-01
Advanced pulsed cryogenic molecular-beam electric deflection methods involving position-sensitive mass spectrometry and 7.87-eV ionizing radiation were used to measure the polarizabilities of more than half of the metallic elements in the Periodic Table. Concurrent Stern-Gerlach deflection measurements verified the ground-state condition of the measured atoms. Comparison with state-of-the-art calculations exposes significant systematic and isolated discrepancies throughout the Periodic Table.
Periodic Striped Ground States in Ising Models with Competing Interactions
NASA Astrophysics Data System (ADS)
Giuliani, Alessandro; Seiringer, Robert
2016-11-01
We consider Ising models in two and three dimensions, with short range ferromagnetic and long range, power-law decaying, antiferromagnetic interactions. We let J be the ratio between the strength of the ferromagnetic to antiferromagnetic interactions. The competition between these two kinds of interactions induces the system to form domains of minus spins in a background of plus spins, or vice versa. If the decay exponent p of the long range interaction is larger than d + 1, with d the space dimension, this happens for all values of J smaller than a critical value J c ( p), beyond which the ground state is homogeneous. In this paper, we give a characterization of the infinite volume ground states of the system, for p > 2 d and J in a left neighborhood of J c ( p). In particular, we prove that the quasi-one-dimensional states consisting of infinite stripes ( d = 2) or slabs ( d = 3), all of the same optimal width and orientation, and alternating magnetization, are infinite volume ground states. Our proof is based on localization bounds combined with reflection positivity.
Coherent Transfer of Photoassociated Molecules into the Rovibrational Ground State
NASA Astrophysics Data System (ADS)
Inouye, Shin
2011-05-01
Recently, there have been impressive advances in methods of creating ultracold molecules from ultracold atomic gases. One of the key technologies used there is Stimulated Raman Adiabatic Passage (STIRAP), which has been successfully used for transferring Feshbach molecules into the rovibrational ground state. Since STIRAP relies on quantum coherence, it is unclear if STIRAP is also useful for non-polarized sample, like photo-associated molecules in a magneto-optical trap. Here we report on the SITRAP transfer of weakly bound molecules produced by photoassociation (PA). Laser cooled 41 K and 87 Rb atoms were first photo-associated into loosely-bound molecules in the X 1 Σ potential. Using v = 41, J = 1 level in the (3) 1 Σ potential as an intermediate level, we succeeded in transferring molecules in the v = 91, J = 0 level into the absolute ground state (X 1 Σ , v = 0, N = 0). High-resolution spectroscopy based on the coherent transfer revealed the hyperfine structure of both weakly-bound and tightly-bound molecules. Our results show that a pure sample of ultracold ground-state molecules is achieved via the all-optical association of laser-cooled atoms, opening possibilities to coherently manipulate a wide variety of molecules.In collaboration with Kiyotaka Aikawa, Kohei Oasa, University of Tokyo; Masahito Ueda, University of Tokyo, JST, ERATO; Jun Kobayashi, University of Tokyo; and Tetsuo Kishimoto, University of Electro-Communications.
Periodic Striped Ground States in Ising Models with Competing Interactions
NASA Astrophysics Data System (ADS)
Giuliani, Alessandro; Seiringer, Robert
2016-06-01
We consider Ising models in two and three dimensions, with short range ferromagnetic and long range, power-law decaying, antiferromagnetic interactions. We let J be the ratio between the strength of the ferromagnetic to antiferromagnetic interactions. The competition between these two kinds of interactions induces the system to form domains of minus spins in a background of plus spins, or vice versa. If the decay exponent p of the long range interaction is larger than d + 1, with d the space dimension, this happens for all values of J smaller than a critical value J c (p), beyond which the ground state is homogeneous. In this paper, we give a characterization of the infinite volume ground states of the system, for p > 2d and J in a left neighborhood of J c (p). In particular, we prove that the quasi-one-dimensional states consisting of infinite stripes (d = 2) or slabs (d = 3), all of the same optimal width and orientation, and alternating magnetization, are infinite volume ground states. Our proof is based on localization bounds combined with reflection positivity.
Anomalous magnetic hyperfine structure of the 229Th ground-state doublet in muonic atoms
NASA Astrophysics Data System (ADS)
Tkalya, E. V.
2016-07-01
The magnetic hyperfine (MHF) splitting of the ground and low-energy 3 /2+(7.8 ±0.5 eV) levels in the 229Th nucleus in the muonic atom (μ1S1 /2 -229Th) * is calculated considering the distribution of the nuclear magnetization in the framework of the collective nuclear model with wave functions of the Nilsson model for the unpaired neutron. It is shown that (a) deviation of the MHF structure of the isomeric state exceeds 100% from its value for a pointlike nuclear magnetic dipole (the order of sublevels is reversed); (b) partial inversion of levels of the 229Th ground-state doublet and spontaneous decay of the ground state to the isomeric state occur; (c) the E 0 transition, which is sensitive to differences in the mean-square charge radii of the doublet states, is possible between mixed sublevels with F =2 ; and (d) MHF splitting of the 3 /2+ isomeric state may be in the optical range for certain values of the intrinsic gK factor and a reduced probability of a nuclear transition between the isomeric and the ground states.
Tunable Splitting of the Ground-State Degeneracy in Quasi-One-Dimensional Parafermion Systems.
Chen, Chun; Burnell, F J
2016-03-11
Systems with topologically protected ground-state degeneracies are currently of great interest due to their potential applications in quantum computing. In practice, this degeneracy is never exact, and the magnitude of the ground-state degeneracy splitting imposes constraints on the time scales over which information is topologically protected. In this Letter, we use an instanton approach to evaluate the splitting of topological ground-state degeneracy in quasi-1D systems with parafermion zero modes, in the specific case where parafermions are realized by inducing a superconducting gap in pairs of fractional quantum Hall edges. We show that, like 1D topological superconducting wires, this splitting has an oscillatory dependence on the chemical potential, which arises from an intrinsic Berry phase that produces interference between distinct instanton tunneling events. These Berry phases can be mapped to chiral phases in a (dual) quantum clock model using a Fradkin-Kadanoff transformation. Comparing our low-energy spectrum to that of phenomenological parafermion models allows us to evaluate the real and imaginary parts of the hopping integral between adjacent parafermionic zero modes as functions of the chemical potential. PMID:27015499
Tunable Splitting of the Ground-State Degeneracy in 1D Parafermionic Wires
NASA Astrophysics Data System (ADS)
Chen, Chun; Burnell, Fiona
Systems with topologically protected ground-state degeneracies are currently of great interest due to their potential applications in quantum computing. In practise this degeneracy is never exact, and the magnitude of the ground-state degeneracy splitting imposes constraints on the timescales over which information is topologically protected. In this Letter we use an instanton approach to evaluate the splitting of topological ground-state degeneracy in quasi-1D systems with parafermion zero modes, in the specific case where parafermions are realized by inducing a superconducting gap in pairs of fractional quantum Hall (FQH) edges. We show that, like 1D topological superconducting wires, this splitting has an oscillatory dependence on the chemical potential, which arises from an intrinsic Berry phase that produces interference between distinct instanton tunneling events. These Berry phases can be mapped to chiral phases in a (dual) quantum clock model using a Fradkin-Kadanoff transformation. Comparing our low-energy spectrum to that of phenomenological parafermion models allows us to evaluate the real and imaginary parts of the hopping integral between adjacent parafermionic zero modes as functions of the chemical potential.
Tunable Splitting of the Ground-State Degeneracy in Quasi-One-Dimensional Parafermion Systems
NASA Astrophysics Data System (ADS)
Chen, Chun; Burnell, F. J.
2016-03-01
Systems with topologically protected ground-state degeneracies are currently of great interest due to their potential applications in quantum computing. In practice, this degeneracy is never exact, and the magnitude of the ground-state degeneracy splitting imposes constraints on the time scales over which information is topologically protected. In this Letter, we use an instanton approach to evaluate the splitting of topological ground-state degeneracy in quasi-1D systems with parafermion zero modes, in the specific case where parafermions are realized by inducing a superconducting gap in pairs of fractional quantum Hall edges. We show that, like 1D topological superconducting wires, this splitting has an oscillatory dependence on the chemical potential, which arises from an intrinsic Berry phase that produces interference between distinct instanton tunneling events. These Berry phases can be mapped to chiral phases in a (dual) quantum clock model using a Fradkin-Kadanoff transformation. Comparing our low-energy spectrum to that of phenomenological parafermion models allows us to evaluate the real and imaginary parts of the hopping integral between adjacent parafermionic zero modes as functions of the chemical potential.
Sign structure and ground-state properties for a spin-S t-J chain
NASA Astrophysics Data System (ADS)
Wang, Qing-Rui; Ye, Peng
2014-07-01
The antiferromagnetic Heisenberg spin chain of odd spin S is in the Haldane phase with several defining physical properties, such as thermodynamical ground-state degeneracy, symmetry-protected edge states, and nonzero string order parameter. If nonzero hole concentration δ and hole hopping energy t are considered, the spin chain is replaced by a spin-S t-J chain. The motivation of this paper is to generalize the discussions of the Haldane phase to the doped spin chain. The first result of this paper is that, for the model considered here, the Z2 sign structure in the usual Ising basis can be totally removed by two consecutive unitary transformations consisting of a spatially local one and a nonlocal one. Direct from the sign structure, the second result of this paper is that the Marshall theorem and the Lieb-Mattis theorem for pure spin systems are generalized to the t-J chain for arbitrary S and δ. A corollary of the theorem provides us with the ground-state degeneracy in the thermodynamic limit. The third result of this paper is about the phase diagram. We show that the defining properties of the Haldane phase survive in the small t /J limit. The large t /J phase supports a gapped spin sector with similar properties (ground-state degeneracy, edge state, and string order parameter) of the Haldane chain, although the charge sector is gapless.
Impurity-to-band activation energy in phosphorus doped diamond
NASA Astrophysics Data System (ADS)
Stenger, I.; Pinault-Thaury, M.-A.; Kociniewski, T.; Lusson, A.; Chikoidze, E.; Jomard, F.; Dumont, Y.; Chevallier, J.; Barjon, J.
2013-08-01
The value of the impurity-to-band activation energy EA of a dopant is a basic feature of the electrical conductivity of semiconductors. Various techniques were used to determine EA in n-type diamond doped with phosphorus, giving values of EA varying from 0.43 eV to 0.63 eV, the value EA of 0.6 eV being commonly accepted for the ionization energy of phosphorus donors in diamond. Nevertheless, up to now, the dispersion of the experimental values of EA remains unexplained. In this work, we investigate the electrical properties of a set of n-type diamond homoepitaxial films with different phosphorus concentrations by Hall effect measurements in order to deduce EA and to understand the evolution of this energy with the dopant concentration. We show that, below 2 × 1019 cm-3 phosphorus, the decrease of EA is mainly controlled by the concentration of ionized defects resulting from the donor compensation. The role of ionized defects in the decrease of EA is analyzed on the basis of existing models adapted to the case of diamond. The proposed model provides a correct description of the experimental data. It can be used to quantitatively predict the activation energy of phosphorus in n-type diamond for given donor and compensating acceptor concentrations.
Ground-state properties of a dilute homogeneous Bose gas of hard disks in two dimensions
Mazzanti, F.; Polls, A.; Fabrocini, A.
2005-03-01
The energy and structure of a dilute hard-disks Bose gas are studied in the framework of a variational many-body approach based on a Jastrow correlated ground-state wave function. The asymptotic behaviors of the radial distribution function and the one-body density matrix are analyzed after solving the Euler equation obtained by a free minimization of the hypernetted chain energy functional. Our results show important deviations from those of the available low density expansions, already at gas parameter values x{approx}0.001. The condensate fraction in 2D is also computed and found generally lower than the 3D one at the same x.
NASA Astrophysics Data System (ADS)
Jiménez, Andrea
2014-02-01
We study the unexpected asymptotic behavior of the degeneracy of the first few energy levels in the antiferromagnetic Ising model on triangulations of closed Riemann surfaces. There are strong mathematical and physical reasons to expect that the number of ground states (i.e., degeneracy) of the antiferromagnetic Ising model on the triangulations of a fixed closed Riemann surface is exponential in the number of vertices. In the set of plane triangulations, the degeneracy equals the number of perfect matchings of the geometric duals, and thus it is exponential by a recent result of Chudnovsky and Seymour. From the physics point of view, antiferromagnetic triangulations are geometrically frustrated systems, and in such systems exponential degeneracy is predicted. We present results that contradict these predictions. We prove that for each closed Riemann surface S of positive genus, there are sequences of triangulations of S with exactly one ground state. One possible explanation of this phenomenon is that exponential degeneracy would be found in the excited states with energy close to the ground state energy. However, as our second result, we show the existence of a sequence of triangulations of a closed Riemann surface of genus 10 with exactly one ground state such that the degeneracy of each of the 1st, 2nd, 3rd and 4th excited energy levels belongs to O( n), O( n 2), O( n 3) and O( n 4), respectively.
All-optical reconstruction of atomic ground-state population
NASA Astrophysics Data System (ADS)
London, P.; Firstenberg, O.; Shuker, M.; Ron, A.
2010-04-01
The population distribution within the ground state of an atomic ensemble is of great significance in a variety of quantum-optics processes. We present a method to reconstruct the detailed population distribution from a set of absorption measurements with various frequencies and polarizations, by utilizing the differences between the dipole matrix elements of the probed transitions. The technique is experimentally implemented on a thermal rubidium vapor, demonstrating a population-based analysis in two optical-pumping examples. The results are used to verify and calibrate an elaborated numerical model, and the limitations of the reconstruction scheme, which result from the symmetry properties of the dipole matrix elements, are discussed.
The ground state of the Frenkel-Kontorova model
NASA Astrophysics Data System (ADS)
Babushkin, A. Yu.; Abkaryan, A. K.; Dobronets, B. S.; Krasikov, V. S.; Filonov, A. N.
2016-09-01
The continual approximation of the ground state of the discrete Frenkel-Kontorova model is tested using a symmetric algorithm of numerical simulation. A "kaleidoscope effect" is found, which means that the curves representing the dependences of the relative extension of an N-atom chain vary periodically with increasing N. Stairs of structural transitions for N ≫ 1 are analyzed by the channel selection method with the approximation N = ∞. Images of commensurable and incommensurable structures are constructed. The commensurable-incommensurable phase transitions are stepwise.
Ground state solutions for non-autonomous fractional Choquard equations
NASA Astrophysics Data System (ADS)
Chen, Yan-Hong; Liu, Chungen
2016-06-01
We consider the following nonlinear fractional Choquard equation, {(‑Δ)su+u=(1+a(x))(Iα ∗ (|u| p))|u| p‑2uin RN,u(x)→0as |x|→∞, here s\\in (0,1) , α \\in (0,N) , p\\in ≤ft[2,∞ \\right) and \\frac{N-2s}{N+α}<\\frac{1}{p}<\\frac{N}{N+α} . Assume {{\\lim}|x|\\to ∞}a(x)=0 and satisfying suitable assumptions but not requiring any symmetry property on a(x), we prove the existence of ground state solutions for (0.1).
Ground state solutions for non-autonomous fractional Choquard equations
NASA Astrophysics Data System (ADS)
Chen, Yan-Hong; Liu, Chungen
2016-06-01
We consider the following nonlinear fractional Choquard equation, {(-Δ)su+u=(1+a(x))(Iα ∗ (|u| p))|u| p-2uin RN,u(x)→0as |x|→∞, here s\\in (0,1) , α \\in (0,N) , p\\in ≤ft[2,∞ \\right) and \\frac{N-2s}{N+α}<\\frac{1}{p}<\\frac{N}{N+α} . Assume {{\\lim}|x|\\to ∞}a(x)=0 and satisfying suitable assumptions but not requiring any symmetry property on a(x), we prove the existence of ground state solutions for (0.1).
Laboratory rotational ground state transitions of NH3D+ and CF+
NASA Astrophysics Data System (ADS)
Stoffels, A.; Kluge, L.; Schlemmer, S.; Brünken, S.
2016-09-01
Aims: This paper reports accurate laboratory frequencies of the rotational ground state transitions of two astronomically relevant molecular ions, NH3D+ and CF+. Methods: Spectra in the millimetre-wave band were recorded by the method of rotational state-selective attachment of He atoms to the molecular ions stored and cooled in a cryogenic ion trap held at 4 K. The lowest rotational transition in the A state (ortho state) of NH3D+ (JK = 10-00), and the two hyperfine components of the ground state transition of CF+ (J = 1-0) were measured with a relative precision better than 10-7. Results: For both target ions, the experimental transition frequencies agree with recent observations of the same lines in different astronomical environments. In the case of NH3D+ the high-accuracy laboratory measurements lend support to its tentative identification in the interstellar medium. For CF+ the experimentally determined hyperfine splitting confirms previous quantum-chemical calculations and the intrinsic spectroscopic nature of a double-peaked line profile observed in the J = 1-0 transition towards the Horsehead photon-dominated region (PDR).
Probing bulk defect energy bands using generalized charge pumping method
NASA Astrophysics Data System (ADS)
Masuduzzaman, Muhammad; Weir, Bonnie; Alam, Muhammad Ashraful
2012-04-01
The multifrequency charge pumping (CP) technique has long been used to probe the density of defects at the substrate-oxide interface, as well as in the bulk of the oxide of MOS transistors. However, profiling the energy levels of the defects has been more difficult due to the narrow scanning range of the voltage of a typical CP signal, and the uncertainty associated with the defect capture cross-section. In this paper, we discuss a generalized CP method that can identify defect energy bands within a bulk oxide, without requiring separate characterization of the defect capture cross-section. We use the new technique to characterize defects in both fresh and stressed samples of various dielectric compositions. By quantifying the way defects are generated as a function of time, we gain insight into the nature of defect generation in a particular gate dielectric. We also discuss the relative merits of voltage, time, and other variables of CP to probe bulk defect density, and compare the technique with related characterization approaches.
Competing ground states of strongly correlated bosons in the Harper-Hofstadter-Mott model
NASA Astrophysics Data System (ADS)
Natu, Stefan S.; Mueller, Erich J.; Das Sarma, S.
2016-06-01
Using an efficient cluster approach, we study the physics of two-dimensional lattice bosons in a strong magnetic field in the regime where the tunneling is much weaker than the on-site interaction strength. We study both the dilute, hard-core bosons at filling factors much smaller than unity occupation per site and the physics in the vicinity of the superfluid-Mott lobes as the density is tuned away from unity. For hard-core bosons, we carry out extensive numerics for a fixed flux per plaquette ϕ =1 /5 and ϕ =1 /3 . At large flux, the lowest-energy state is a strongly correlated superfluid, analogous to He-4, in which the order parameter is dramatically suppressed, but nonzero. At filling factors ν =1 /2 ,1 , we find competing incompressible states which are metastable. These appear to be commensurate density wave states. For small flux, the situation is reversed and the ground state at ν =1 /2 is an incompressible density wave solid. Here, we find a metastable lattice supersolid phase, where superfluidity and density wave order coexist. We then perform careful numerical studies of the physics near the vicinity of the Mott lobes for ϕ =1 /2 and ϕ =1 /4 . At ϕ =1 /2 , the superfluid ground state has commensurate density wave order. At ϕ =1 /4 , incompressible phases appear outside the Mott lobes at densities n =1.125 and n =1.25 , corresponding to filling fractions ν =1 /2 and 1, respectively. These phases, which are absent in single-site mean-field theory, are metastable and have slightly higher energy than the superfluid, but the energy difference between them shrinks rapidly with increasing cluster size, suggestive of an incompressible ground state. We thus explore the interplay between Mott physics, magnetic Landau levels, and superfluidity, finding a rich phase diagram of competing compressible and incompressible states.
The valence-fluctuating ground state of plutonium
Janoschek, Marc; Das, Pinaki; Chakrabarti, Bismayan; Abernathy, Douglas L.; Lumsden, Mark D.; Lawrence, John M.; Thompson, Joe D.; Lander, Gerard H.; Mitchell, Jeremy N.; Richmond, Scott; et al
2015-07-10
A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise because of the competition of localized and itinerant electronic degrees of freedom. Although the respective limits of well-localized or entirely itinerant ground states are well understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and nonbonding configurations. In addition, our study reveals that the ground state of plutonium is governed bymore » valence fluctuations, that is, a quantum mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium’s magnetism but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials.« less
Spatial competition of the ground states in 1111 iron pnictides
NASA Astrophysics Data System (ADS)
Lang, G.; Veyrat, L.; Gräfe, U.; Hammerath, F.; Paar, D.; Behr, G.; Wurmehl, S.; Grafe, H.-J.
2016-07-01
Using nuclear quadrupole resonance, the phase diagram of 1111 R FeAsO1 -xFx (R =La , Ce, Sm) iron pnictides is constructed as a function of the local charge distribution in the paramagnetic state, which features low-doping-like (LD-like) and high-doping-like (HD-like) regions. Compounds based on magnetic rare earths (Ce, Sm) display a unified behavior, and comparison with La-based compounds reveals the detrimental role of static iron 3 d magnetism on superconductivity, as well as a qualitatively different evolution of the latter at high doping. It is found that the LD-like regions fully account for the orthorhombicity of the system, and are thus the origin of any static iron magnetism. Orthorhombicity and static magnetism are not hindered by superconductivity but limited by dilution effects, in agreement with two-dimensional (2D) (respectively three-dimensional) nearest-neighbor square lattice site percolation when the rare earth is nonmagnetic (respectively magnetic). The LD-like regions are not intrinsically supportive of superconductivity, contrary to the HD-like regions, as evidenced by the well-defined Uemura relation between the superconducting transition temperature and the superfluid density when accounting for the proximity effect. This leads us to propose a complete description of the interplay of ground states in 1111 pnictides, where nanoscopic regions compete to establish the ground state through suppression of superconductivity by static magnetism, and extension of superconductivity by proximity effect.
Magnetic ground state of semiconducting transition-metal trichalcogenide monolayers
Sivadas, Nikhil; Daniels, Matthew W.; Swendsen, Robert H.; Okamoto, Satoshi; Xiao, Di
2015-06-16
Layered transition-metal trichalcogenides with the chemical formula ABX_{3} have attracted recent interest as potential candidates for two-dimensional magnets. Using first-principles calculations within density functional theory, we investigate the magnetic ground states of monolayers of Mn- and Cr-based semiconducting trichalcogenides.We show that the second and third nearest-neighbor exchange interactions (J_{2} and J_{3}) between magnetic ions, which have been largely overlooked in previous theoretical studies, are crucial in determining the magnetic ground state. Specifically, we find that monolayer CrSiTe_{3} is an antiferromagnet with a zigzag spin texture due to significant contribution from J_{3}, whereas CrGeTe_{3} is a ferromagnet with a Curie temperature of 106 K. Monolayers of Mn compounds (MnPS_{3} and MnPSe_{3}) always show antiferromagnetic N eel order. We identify the physical origin of various exchange interactions, and demonstrate that strain can be an effective knob for tuning the magnetic properties. Possible magnetic ordering in the bulk is also discussed. In conclusion, our study suggests that ABX_{3} can be a promising platform to explore two-dimensional magnetic phenomena.
Magnetic ground state of semiconducting transition-metal trichalcogenide monolayers
Sivadas, Nikhil; Daniels, Matthew W.; Swendsen, Robert H.; Okamoto, Satoshi; Xiao, Di
2015-06-16
Layered transition-metal trichalcogenides with the chemical formula ABX3 have attracted recent interest as potential candidates for two-dimensional magnets. Using first-principles calculations within density functional theory, we investigate the magnetic ground states of monolayers of Mn- and Cr-based semiconducting trichalcogenides.We show that the second and third nearest-neighbor exchange interactions (J2 and J3) between magnetic ions, which have been largely overlooked in previous theoretical studies, are crucial in determining the magnetic ground state. Specifically, we find that monolayer CrSiTe3 is an antiferromagnet with a zigzag spin texture due to significant contribution from J3, whereas CrGeTe3 is a ferromagnet with a Curie temperaturemore » of 106 K. Monolayers of Mn compounds (MnPS3 and MnPSe3) always show antiferromagnetic N eel order. We identify the physical origin of various exchange interactions, and demonstrate that strain can be an effective knob for tuning the magnetic properties. Possible magnetic ordering in the bulk is also discussed. In conclusion, our study suggests that ABX3 can be a promising platform to explore two-dimensional magnetic phenomena.« less
Au42: a possible ground-state noble metallic nanotube.
Wang, Jing; Ning, Hua; Ma, Qing-Min; Liu, Ying; Li, You-Cheng
2008-10-01
A large hollow tubelike Au(42) is predicted as a new ground-state configuration based on the scalar relativistic density functional theory. The shape of this new Au(42) cluster is similar to a (5,5) single-wall gold nanotube, the two ends of which are capped by half of a fullerenelike Au(32). In the same way, a series of Au(n) (n = 37, 42, 47, 52, 57, 62, 67, 72, ..., Delta n = 5) tubelike structures has been constructed. The highest occupied molecular orbital-lowest unoccupied molecular orbital gaps suggested a significant semiconductor-conductor alternation in n is an element of [32,47]. Similar to the predictions and speculation of Daedalus [D. E. H. Jones, New Sci. 32, 245 (1966); E. Osawa, Superaromaticity (Kagaku, Kyoto, 1970), Vol. 25, pp. 854-863; Z. Yoshida and E. Osawa, Aromaticity Chemical Monograph (Kagaku Dojin, Kyoto, Japan, 1971), Vol. 22, pp. 174-176; D. A. Bochvar and E. G. Gal'pern, Dokl. Akad. Nauk SSSR 209, 610 (1973)], here a large hollow ground-state gold nanotube was predicted theoretically. PMID:19045114
Au42: A possible ground-state noble metallic nanotube
NASA Astrophysics Data System (ADS)
Wang, Jing; Ning, Hua; Ma, Qing-Min; Liu, Ying; Li, You-Cheng
2008-10-01
A large hollow tubelike Au42 is predicted as a new ground-state configuration based on the scalar relativistic density functional theory. The shape of this new Au42 cluster is similar to a (5,5) single-wall gold nanotube, the two ends of which are capped by half of a fullerenelike Au32. In the same way, a series of Aun (n =37,42,47,52,57,62,67,72,…, Δn =5) tubelike structures has been constructed. The highest occupied molecular orbital-lowest unoccupied molecular orbital gaps suggested a significant semiconductor-conductor alternation in n ɛ[32,47]. Similar to the predictions and speculation of Daedalus [D. E. H. Jones, New Sci. 32, 245 (1966); E. Osawa, Superaromaticity (Kagaku, Kyoto, 1970), Vol. 25, pp. 854-863; Z. Yoshida and E. Osawa, Aromaticity Chemical Monograph (Kagaku Dojin, Kyoto, Japan, 1971), Vol. 22, pp. 174-176; D. A. Bochvar and E. G. Gal'pern, Dokl. Akad. Nauk SSSR 209, 610 (1973)], here a large hollow ground-state gold nanotube was predicted theoretically.
Singlet Ground State of the Quantum Antiferromagnet Ba3CuSb2O9
NASA Astrophysics Data System (ADS)
Quilliam, J. A.; Bert, F.; Kermarrec, E.; Payen, C.; Guillot-Deudon, C.; Bonville, P.; Baines, C.; Luetkens, H.; Mendels, P.
2012-09-01
We present local probe results on the honeycomb lattice antiferromagnet Ba3CuSb2O9. Muon spin relaxation measurements in a zero field down to 20 mK show unequivocally that there is a total absence of spin freezing in the ground state. Sb NMR measurements allow us to track the intrinsic susceptibility of the lattice, which shows a maximum at around 55 K and drops to zero in the low-temperature limit. The spin-lattice relaxation rate shows two characteristic energy scales, including a field-dependent crossover to exponential low-temperature behavior, implying gapped magnetic excitations.
Quantum Cohesion Oscillation of Electron Ground State in Low Temperature Laser Plasma
NASA Technical Reports Server (NTRS)
Zhao, Qingxun; Zhang, Ping; Dong, Lifang; Zhang, Kaixi
1996-01-01
The development of radically new technological and economically efficient methods for obtaining chemical products and for producing new materials with specific properties requires the study of physical and chemical processes proceeding at temperature of 10(exp 3) to 10(exp 4) K, temperature range of low temperature plasma. In our paper, by means of Wigner matrix of quantum statistical theory, a formula is derived for the energy of quantum coherent oscillation of electron ground state in laser plasma at low temperature. The collective behavior would be important in ion and ion-molecule reactions.
The ground state of the D = 11 supermembrane and matrix models on compact regions
NASA Astrophysics Data System (ADS)
Boulton, Lyonell; Garcia del Moral, Maria Pilar; Restuccia, Alvaro
2016-09-01
We establish a general framework for the analysis of boundary value problems of matrix models at zero energy on compact regions. We derive existence and uniqueness of ground state wavefunctions for the mass operator of the D = 11 regularized supermembrane theory, that is the N = 16 supersymmetric SU (N) matrix model, on balls of finite radius. Our results rely on the structure of the associated Dirichlet form and a factorization in terms of the supersymmetric charges. They also rely on the polynomial structure of the potential and various other supersymmetric properties of the system.
Excitations of {sup 1}P levels of zinc by electron impact on the ground state
Fursa, Dmitry V.; Bray, Igor; Panajotovic, R.; Sevic, D.; Pejcev, V.; Marinkovic, B.P.; Filipovic, D.M.
2005-07-15
We present results of a joint theoretical and experimental investigation of electron scattering from the 4s{sup 2} {sup 1}S ground state of zinc. The 4s4p {sup 1}P{sup o} and 4s5p {sup 1}P{sup o} differential cross sections were measured at scattering angles between 10 degree sign and 150 degree sign and electron-energies of 15, 20, 25, 40, and 60 eV. Corresponding convergent close-coupling calculations have been performed and are compared with experiment.
NASA Astrophysics Data System (ADS)
Ishida, A.; Namba, T.; Asai, S.
2016-03-01
The thermalization parameter of positronium in pure isobutane gas was measured in order to take into account the thermalization effect on precision measurements of the ground-state hyperfine splitting (HFS) of positronium. The momentum-transfer cross section was measured to be {σ }{{m}}=47.2+/- 6.7 {\\mathringA }2 for positroniums with kinetic energy below 0.17 eV. Using this value, our new HFS experiment revealed that the positronium thermalization effect on HFS was as large as 10+/- 2 {ppm}. In this article, we show the details of Ps thermalization measurement, which have not been published before, and also its effect on HFS.
Quantum Unfolding: A program for unfolding electronic energy bands of materials
NASA Astrophysics Data System (ADS)
Zheng, Fawei; Zhang, Ping; Duan, Wenhui
2015-04-01
We present Quantum Unfolding, a Fortran90 program for unfolding first-principles electronic energy bands. It unfolds energy bands accurately by handling the Fourier components of Bloch wavefunctions, which are reconstructed from Wannier functions from Wannier90. Due to the wide application of Wannier90 package and the possibility of focusing only on the most important energy bands, the present code works very conveniently.
Theoretical study of the ground-state structures and properties of niobium hydrides under pressure
NASA Astrophysics Data System (ADS)
Gao, Guoying; Hoffmann, Roald; Ashcroft, N. W.; Liu, Hanyu; Bergara, Aitor; Ma, Yanming
2013-11-01
As part of a search for enhanced superconductivity, we explore theoretically the ground-state structures and properties of some hydrides of niobium over a range of pressures and particularly those with significant hydrogen content. A primary motivation originates with the observation that under normal conditions niobium is the element with the highest superconducting transition temperature (Tc), and moreover some of its compounds are metals again with very high Tc's. Accordingly, combinations of niobium with hydrogen, with its high dynamic energy scale, are also of considerable interest. This is reinforced further by the suggestion that close to its insulator-metal transition, hydrogen may be induced to enter the metallic state somewhat prematurely by the addition of a relatively small concentration of a suitable transition metal. Here, the methods used correctly reproduce some ground-state structures of niobium hydrides at even higher concentrations of niobium. Interestingly, the particular stoichiometries represented by NbH4 and NbH6 are stabilized at fairly low pressures when proton zero-point energies are included. While no paired H2 units are found in any of the hydrides we have studied up to 400 GPa, we do find complex and interesting networks of hydrogens around the niobiums in high-pressure NbH6. The Nb-Nb separations in NbHn are consistently larger than those found in Nb metal at the respective pressures. The structures found in the ground states of the high hydrides, many of them metallic, suggest that the coordination number of hydrogens around each niobium atom grows approximately as 4n in NbHn (n = 1-4), and is as high as 20 in NbH6. NbH4 is found to be a plausible candidate to become a superconductor at high pressure, with an estimated Tc ˜ 38 K at 300 GPa.
GSGPEs: A MATLAB code for computing the ground state of systems of Gross-Pitaevskii equations
NASA Astrophysics Data System (ADS)
Caliari, Marco; Rainer, Stefan
2013-03-01
GSGPEs is a Matlab/GNU Octave suite of programs for the computation of the ground state of systems of Gross-Pitaevskii equations. It can compute the ground state in the defocusing case, for any number of equations with harmonic or quasi-harmonic trapping potentials, in spatial dimension one, two or three. The computation is based on a spectral decomposition of the solution into Hermite functions and direct minimization of the energy functional through a Newton-like method with an approximate line-search strategy. Catalogue identifier: AENT_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AENT_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1417 No. of bytes in distributed program, including test data, etc.: 13673 Distribution format: tar.gz Programming language: Matlab/GNU Octave. Computer: Any supporting Matlab/GNU Octave. Operating system: Any supporting Matlab/GNU Octave. RAM: About 100 MB for a single three-dimensional equation (test run output). Classification: 2.7, 4.9. Nature of problem: A system of Gross-Pitaevskii Equations (GPEs) is used to mathematically model a Bose-Einstein Condensate (BEC) for a mixture of different interacting atomic species. The equations can be used both to compute the ground state solution (i.e., the stationary order parameter that minimizes the energy functional) and to simulate the dynamics. For particular shapes of the traps, three-dimensional BECs can be also simulated by lower dimensional GPEs. Solution method: The ground state of a system of Gross-Pitaevskii equations is computed through a spectral decomposition into Hermite functions and the direct minimization of the energy functional. Running time: About 30 seconds for a single three-dimensional equation with d.o.f. 40 for each spatial direction (test run output).
Bane, Michael K; Robertson, Evan G; Thompson, Christopher D; Medcraft, Chris; Appadoo, Dominique R T; McNaughton, Don
2011-06-21
High resolution FTIR spectra of the short lived species ketenimine have been recorded in the regions 390-1300 cm(-1) and 20-110 cm(-1) using synchrotron radiation. Two thousand six hundred sixty transitions of the ν(7) band centered at 693 cm(-1) and 126 far-IR rotational transitions have been assigned. Rotational and centrifugal distortion parameters for the ν(7) mode were determined and local Fermi and b-axis Coriolis interactions with 2ν(12) are treated. A further refinement of the ground state, ν(12) and ν(8) parameters was also achieved, including the treatment of previously unrecognized ac-axis and ab-axis second order perturbations to the ground state.
The Icosahedral Ti-Zr-Ni Quasicrystal - A Ground State Quasicrystal?
NASA Astrophysics Data System (ADS)
Hennig, R. G.; Carlsson, A. E.; Kelton, K. F.; Henley, C. L.
2001-03-01
The icosahedral Ti-Zr-Ni quasicrystal is known to be thermodynamically stable [1]. Most stable quasicrystals form at high temperatures from the liquid phase. In contrast to those quasicrystals, however, the Ti-Zr-Ni quasicrystal forms at lower temperatures, near 570^circC, by a solid state transformation of crystal phases that are stable at higher temperatures. A decorated canonical cell tiling for the structure of this quasicrystal was determined by a refinement to x-ray and neutron diffraction data and results from ab initio calculations. The energetic stability of the icosahedral Ti-Zr-Ni quasicrystal was investigated by total energy calculations using the density-functional code VASP [2]. The ternary ground state phase diagram for Ti-Zr-Ni was determined. The energy of the structural model of the quasicrystal is found to be lower than the energy of any known competing phase. This result, coupled with the continued stability with long anneals at lower temperatures, strongly suggest that the icosahedral Ti-Zr-Ni quasicrystal is a ground state quasicrystal. [1] K. F. Kelton, W. J. Kim, and R. M. Stroud. Appl. Phys. Let. 70, 3230 (1997). [2] G. Kresse and J. Hafner, Phys. Rev. B47, RC 558 (1993); G. Kresse and J. Furthmüller, Phys. Rev. B54, 11169 (1996).
ERIC Educational Resources Information Center
Precker, Jurgen W.
2007-01-01
The wavelength of the light emitted by a light-emitting diode (LED) is intimately related to the band-gap energy of the semiconductor from which the LED is made. We experimentally estimate the band-gap energies of several types of LEDs, and compare them with the energies of the emitted light, which ranges from infrared to white. In spite of…
Antiferromagnetic Spin-S Chains with Exactly Dimerized Ground States
NASA Astrophysics Data System (ADS)
Michaud, Frédéric; Vernay, François; Manmana, Salvatore R.; Mila, Frédéric
2012-03-01
We show that spin S Heisenberg spin chains with an additional three-body interaction of the form (Si-1·Si)(Si·Si+1)+H.c. possess fully dimerized ground states if the ratio of the three-body interaction to the bilinear one is equal to 1/[4S(S+1)-2]. This result generalizes the Majumdar-Ghosh point of the J1-J2 chain, to which the present model reduces for S=1/2. For S=1, we use the density matrix renormalization group method to show that the transition between the Haldane and the dimerized phases is continuous with a central charge c=3/2. Finally, we show that such a three-body interaction appears naturally in a strong-coupling expansion of the Hubbard model, and we discuss the consequences for the dimerization of actual antiferromagnetic chains.
Ground state of naphthyl cation: Singlet or triplet?
Dutta, Achintya Kumar; Vaval, Nayana Pal, Sourav; Manohar, Prashant U.
2014-03-21
We present a benchmark theoretical investigation on the electronic structure and singlet-triplet(S-T) gap of 1- and 2-naphthyl cations using the CCSD(T) method. Our calculations reveal that the ground states of both the naphthyl cations are singlet, contrary to the results obtained by DFT/B3LYP calculations reported in previous theoretical studies. However, the triplet states obtained in the two structural isomers of naphthyl cation are completely different. The triplet state in 1-naphthyl cation is (π,σ) type, whereas in 2-naphthyl cation it is (σ,σ{sup ′}) type. The S-T gaps in naphthyl cations and the relative stability ordering of the singlet and the triplet states are highly sensitive to the basis-set quality as well as level of correlation, and demand for inclusion of perturbative triples in the coupled-cluster ansatz.
Experimental Proposal to Detect Topological Ground State Degeneracy
NASA Astrophysics Data System (ADS)
Barkeshli, Maissam; Oreg, Yuval; Qi, Xiao-Liang
2014-03-01
One of the most profound features of topologically ordered states of matter, such as the fractional quantum Hall (FQH) states, is that they possess topology-dependent ground state degeneracies that are robust to all local perturbations. Here we present the first proposal to directly detect these topological degeneracies in an experimentally accessible setup. The detection scheme uses nonlinear electrical conductance measurements in a double layer FQH system, with appropriately patterned top and bottom gates. We propose two experimental platforms; in the first, the detection of topo- logically degenerate states coincides with the detection of ZN parafermion zero modes. We map the relevant physics to a single-channel ZN quantum impurity model, providing a novel generalization of the Kondo model. Our proposal can also be adapted to detect the ZN parafermion zero modes recently discovered in FQH line junctions proximitized with superconductivity.
NEW GROUND-STATE MEASUREMENTS OF ETHYL CYANIDE
Brauer, Carolyn S.; Pearson, John C.; Drouin, Brian J.; Yu, Shanshan
2009-09-01
The spectrum of ethyl cyanide, or propionitrile (CH{sub 3}CH{sub 2}CN), has been repeatedly observed in the interstellar medium with large column densities and surprisingly high temperatures in hot core sources. The construction of new, more sensitive, observatories accessing higher frequencies such as Herschel, ALMA, and SOFIA have made it important to extend the laboratory data for ethyl cyanide to coincide with the capabilities of the new instruments. We report extensions of the laboratory measurements of the rotational spectrum of ethyl cyanide in its ground vibrational state to 1.6 THz. A global analysis of the ground state, which includes all of the previous data and 3356 newly assigned transitions, has been fitted to within experimental error to J = 132, K = 36, using both Watson A-reduced and Watson S-reduced Hamiltonians.
Measured Atomic Ground State Polarizabilities of 35 Metallic Elements
NASA Astrophysics Data System (ADS)
Indergaard, John; Ma, Lei; Zhang, Baiqian; Larkin, Ilia; Moro, Ramiro; de Heer, Walter
2015-03-01
Advanced pulsed cryogenic molecular beam electric deflection methods utilizing a position-sensitive mass spectrometer and 7.87 eV ionizing radiation were used to measure the polarizabilities of more than half of the metallic elements in the periodic table for the first time. These measurements increase the total number of experimentally obtained atomic polarizabilities from 23 to 57. Concurrent Stern-Gerlach deflection measurements verified the ground state condition of the measured atoms. Generating higher temperature beams allowed for the comparison of relative populations of the ground and excited states in order to extract the true temperature of the atomic beam, which followed the nominal temperature closely over a wide temperature range. Comparison of newly measured polarizabilities with state-of-the-art calculations exposes significant systematic and isolated discrepancies throughout the periodic table. Cluster Lab at Georgia Tech.
Absence of Quantum Time Crystals in Ground States
NASA Astrophysics Data System (ADS)
Watanabe, Haruki; Oshikawa, Masaki
2015-03-01
In analogy with crystalline solids around us, Wilczek recently proposed the idea of ``time crystals'' as phases that spontaneously break the continuous time translation into a discrete subgroup. The proposal stimulated further studies and vigorous debates whether it can be realized in a physical system. However, a precise definition of the time crystal is needed to resolve the issue. Here we first present a definition of time crystals based on the time-dependent correlation functions of the order parameter. We then prove a no-go theorem that rules out the possibility of time crystals defined as such, in the ground state of a general Hamiltonian which consists of only short-range interactions.
Diagrammatic perturbation theory - The ground state of the carbon monosulfide molecule
NASA Technical Reports Server (NTRS)
Wilson, S.
1977-01-01
Diagrammatic many-body perturbation theory is employed in a study of the ground state of the carbon monosulfide molecule for bond lengths close to the equilibrium value. The calculations are complete through third order in the energy within the algebraic approximation. Two different zero-order Hamiltonians are considered, and all two-, three-, and four-body terms are determined for the corresponding perturbation expansions. Many-body effects are found to be very important. Pade approximants to the energy expansion are constructed, and upper bounds evaluated. Almost 53 percent of the estimated correlation energy is recovered. The variation of components of the correlation energy with nuclear separation is investigated. Spectroscopic constants are also calculated.
NASA Astrophysics Data System (ADS)
Zhao, G. L.; Bagayoko, D.; Fan, J. D.
1998-03-01
The III-V nitrides are viewed as new semiconductors for optoelectronic applications in the blue and UV wavelengths and, more recently, as high-power, high-temperature electronic devices. However, a reliable prediction of the band gap and the low energy conduction bands had, until now, remained a problem in ab initio computations. A spurious effect of the variational procedure and of basis sets is shown to be a source of this problem. We present first principle computational steps that avoid this effect. We applied our new approach to calculate the electronic structure of III-V gallium-nitride using a local density approximation (LDA) for the exchange-correlation potential. Our calculated electronic structure and band gap, for an optimum basis set, agree qualitatively and quantitatively with experiment. *Work supported in part by funding from the Department of the Navy, Office of Naval Research (ONR), and from the Physics Graduate Program at Southern University and A & M College.
Gad, Kh.
2012-10-15
We have calculated the ground-state energy of the doubly magic nucleus {sup 56}Ni within the framework of the Green's function using the CD-Bonn and N{sup 3}LO nucleon-nucleon potentials. For the sake of comparison, the same calculations are performed using the Brueckner-Hartree-Fock approximation. Both the continuous and conventional choices of single particle energies are used. Additional binding energy is obtained from the inclusion of the hole-hole scattering term within the framework of the Green function approach. In this study, comparison of the calculated ground-state energies, obtained by using the Brueckner-Hartree-Fock approach using continuous choice and different nucleon-nucleon potentials, with the experimental value is accomplished. The results show good agreement between the calculated values and the experimental one for the {sup 56}Ni nucleus. The sensitivity of our results to the choice of the model space is examined.
Cluster rotational bands in 11B
NASA Astrophysics Data System (ADS)
Danilov, A. N.; Demyanova, A. S.; Ogloblin, A. A.; Belyaeva, T. L.; Goncharov, S. A.; Trzaska, W.
2016-05-01
Differential cross-sections of 11B+α inelastic scattering at E(α) =65 MeV leading to most of the known 11B states at excitation energies up to 14 MeV were measured [1]. The data analysis was done using Modified diffraction model (MDM) [2] allowing determining radii of excited states. Radii of the states with excitation energies less than ˜ 7 MeV coincide with the radius of the ground state with an accuracy not less than 0.1 - 0.15 fm. This result is consistent with traditional view on shell structure of low-lying states in 11B. Most of the observed high-energy excited states are distributed among four rotational bands. Moments of inertia of band states are close to the moment of inertia of the Hoyle state of 12C. The calculated radii, related to these bands, are 0.7 - 1.0 fm larger than the radius of the ground state, and are close to the Hoyle state radius. These results are in agreement with existing predictions about various cluster structure of 11B at high excitation energies.
Hartree-Fock many-body perturbation theory for nuclear ground-states
NASA Astrophysics Data System (ADS)
Tichai, Alexander; Langhammer, Joachim; Binder, Sven; Roth, Robert
2016-05-01
We investigate the order-by-order convergence behavior of many-body perturbation theory (MBPT) as a simple and efficient tool to approximate the ground-state energy of closed-shell nuclei. To address the convergence properties directly, we explore perturbative corrections up to 30th order and highlight the role of the partitioning for convergence. The use of a simple Hartree-Fock solution for the unperturbed basis leads to a convergent MBPT series for soft interactions, in contrast to the divergent MBPT series obtained with a harmonic oscillator basis. For larger model spaces and heavier nuclei, where a direct high-order MBPT calculation is not feasible, we perform third-order calculations and compare to advanced ab initio coupled-cluster results for the same interactions and model spaces. We demonstrate that third-order MBPT provides ground-state energies for nuclei up into the tin isotopic chain in excellent agreement with the best available coupled-cluster calculations at a fraction of the computational cost.
The magnetic ground state and relationship to Kitaev physics in α-RuCl3
NASA Astrophysics Data System (ADS)
Banerjee, Arnab
The 2D Kitaev candidate alpha-RuCl3 consists of stacked honeycomb layers weakly coupled by Van der Waals interactions. Here we report the measurements of bulk properties and neutron diffraction in both powder and single crystal samples. Our results show that the full three dimensional magnetic ground state is highly pliable with at least two dominant phases corresponding to two different out-of-plane magnetic orders. They have different Neel temperatures dependent on the stacking of the 2D layers, such as a broad magnetic transition at TN = 14 K as observed in phase-pure powder samples, or a sharp magnetic transition at a lower TN = 7 K as observed in homogeneous single crystals with no evidence for stacking faults. The magnetic refinements of the neutron scattering data will be discussed, which in all cases shows the in-plane magnetic ground state is the zigzag phase common in Kitaev related materials including the honeycomb lattice Iridates. Inelastic neutron scattering in all cases shows that this material consistently exhibit strong two-dimensional magnetic fluctuations leading to a break-down of the classical spin-wave picture. Work performed at ORNL is supported by U.S. Dept. of Energy, Office of Basic Energy Sciences and Office of User Facilities Division.
Biradical character in the ground state of [Mn@Si12](+): a DFT and CASPT2 study.
Arcisauskaite, Vaida; Fijan, Domagoj; Spivak, Mariano; Graaf, Coen de; McGrady, John E
2016-09-14
Both density functional theory and multi-configurational ab initio (CASPT2) calculations are used to explore the potential energy surface of the hexagonal prismatic cluster [Mn@Si12](+). Unlike isoelectronic Cr@Si12, the ground state is a biradical, with triplet and open-shell singlet states lying very close in energy. The results are discussed in the context of recent experimental studies using infra-red multiple photon dissociation spectroscopy and X-ray MCD spectroscopy. PMID:27524177
Bao, Xiaoguang; Hrovat, David; Borden, Weston; Wang, Xue B.
2013-03-20
Cyclobutane-1,2,3,4-tetraone has been both predicted and found to have a triplet ground state, in which a b2g MO and an a2u MO is each singly occupied. In contrast, (CO)5 and (CO)6 have each been predicted to have a singlet ground state. This prediction has been tested by generating the (CO)5 - and (CO)6 - anions in the gas-phase by electrospray vaporization of solutions of, respectively, the croconate (CO)52- and rhodizonate (CO)62- dianions. The negative ion photoelectron (NIPE) spectra of the (CO)5•- radical anion give electron affinity (EA) = 3.830 eV and a singlet ground state for (CO)5, with the triplet higher in energy by 0.850 eV (19.6 kcal/mol). The NIPE spectra of the (CO)6•- radical anion give EA = 3.785 eV and a singlet ground state for (CO)6, with the triplet higher in energy by 0.915 eV (21.1 kcal/mol). (RO)CCSD(T)/aug-cc-pVTZ//(U)B3LYP/6-311+G(2df) calculations give EA values that are only ca. 1 kcal/mol lower than those measured and EST values that are only 2 - 3 kcal/mol higher than those obtained from the NIPE spectra. Thus, the calculations support the interpretations of the NIPE spectra and the finding, based on the spectra, that (CO)5 and (CO)6 both have a singlet ground state.
Esser, Birgit
2015-03-21
A novel class of cyclic conjugated molecules, composed of annelated five- and six-membered rings, is proposed and theoretically investigated using density functional theory and multireference methods with regards to their structures, strain energies, aromaticity (NICS values), electronic ground states, band gaps, and the effect of substituents. These [5.5.6]ncyclacenes are predicted to be low band gap materials (below 1 eV) with, depending on their size, closed-shell singlet ground states. The strain energies from n = 4 upwards lie in the range of the synthetically known [n]cycloparaphenylenes. An investigation of the effect of rim-substitution by methyl, alkynyl, thiomethyl or phenyl groups on the electronic ground states showed that thiomethyl-substitution leads to [5.5.6]ncyclacenes with closed-shell singlet ground states for all sizes n investigated. PMID:25700011
Esser, Birgit
2015-03-21
A novel class of cyclic conjugated molecules, composed of annelated five- and six-membered rings, is proposed and theoretically investigated using density functional theory and multireference methods with regards to their structures, strain energies, aromaticity (NICS values), electronic ground states, band gaps, and the effect of substituents. These [5.5.6]ncyclacenes are predicted to be low band gap materials (below 1 eV) with, depending on their size, closed-shell singlet ground states. The strain energies from n = 4 upwards lie in the range of the synthetically known [n]cycloparaphenylenes. An investigation of the effect of rim-substitution by methyl, alkynyl, thiomethyl or phenyl groups on the electronic ground states showed that thiomethyl-substitution leads to [5.5.6]ncyclacenes with closed-shell singlet ground states for all sizes n investigated.
Atanasov, Mihial; Comba, Peter; Daul, Claude A; Hauser, Andreas
2007-09-20
The topology of the ground-state potential energy surface of M(CN)(6) with orbitally degenerate (2)T(2g) (M = Ti(III) (t(2g)(1)), Fe(III) and Mn(II) (both low-spin t(2g)(5))) and (3)T(1g) ground states (M = V(III) (t(2g)(2)), Mn(III) and Cr(II) (both low-spin t(2g)(4))) has been studied with linear and quadratic Jahn-Teller coupling models in the five-dimensional space of the epsilon(g) and tau(2g) octahedral vibrations (Tg[symbol: see text](epsilon(g)+tau(2g)) Jahn-Teller coupling problem (T(g) = (2)T(2g), (3)T(1g))). A procedure is proposed to give access to all vibronic coupling parameters from geometry optimization with density functional theory (DFT) and the energies of a restricted number of Slater determinants, derived from electron replacements within the t(2g)(1,5) or t(2g)(2,4) ground-state electronic configurations. The results show that coupling to the tau(2g) bending mode is dominant and leads to a stabilization of D(3d) structures (absolute minima on the ground-state potential energy surface) for all complexes considered, except for [Ti(CN)(6)](3-), where the minimum is of D(4h) symmetry. The Jahn-Teller stabilization energies for the D3d minima are found to increase in the order of increasing CN-M pi back-donation (Ti(III) < V(III) < Mn(III) < Fe(III) < Mn(II) < Cr(II)). With the angular overlap model and bonding parameters derived from angular distortions, which correspond to the stable D(3d) minima, the effect of configuration interaction and spin-orbit coupling on the ground-state potential energy surface is explored. This approach is used to correlate Jahn-Teller distortion parameters with structures from X-ray diffraction data. Jahn-Teller coupling to trigonal modes is also used to reinterpret the anisotropy of magnetic susceptibilities and g tensors of [Fe(CN)(6)](3-), and the (3)T(1g) ground-state splitting of [Mn(CN)(6)](3-), deduced from near-IR spectra. The implications of the pseudo Jahn-Teller coupling due to t(2g)-e(g) orbital mixing via
Direct experimental evidence for a multiparticle-hole ground state configuration of deformed 33Mg
NASA Astrophysics Data System (ADS)
Datta, Ushasi; Rahaman, A.; Aumann, T.; Beceiro-Novo, S.; Boretzky, K.; Caesar, C.; Carlson, B. V.; Catford, W. N.; Chakraborty, S.; Chartier, M.; Cortina-Gil, D.; de Angelis, G.; Diaz Fernandez, P.; Emling, H.; Ershova, O.; Fraile, L. M.; Geissel, H.; Gonzalez-Diaz, D.; Jonson, B.; Johansson, H.; Kalantar-Nayestanaki, N.; Kröll, T.; Krücken, R.; Kurcewicz, J.; Langer, C.; Le Bleis, T.; Leifels, Y.; Marganiec, J.; Münzenberg, G.; Najafi, M. A.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Plag, R.; Reifarth, R.; Ricciardi, V.; Rossi, D.; Scheit, H.; Scheidenberger, C.; Simon, H.; Taylor, J. T.; Togano, Y.; Typel, S.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Weigand, M.; Winfield, J. S.; Yakorev, D.; Zoric, M.
2016-09-01
The first direct experimental evidence of a multiparticle-hole ground state configuration of the neutron-rich 33Mg isotope has been obtained via intermediate energy (400 A MeV) Coulomb dissociation measurement. The major part ˜(70 ±13 )% of the cross section is observed to populate the excited states of 32Mg after the Coulomb breakup of 33Mg. The shapes of the differential Coulomb dissociation cross sections in coincidence with different core excited states favor that the valence neutron occupies both the s1 /2 and p3 /2 orbitals. These experimental findings suggest a significant reduction and merging of s d -p f shell gaps at N ˜20 and 28. The ground state configuration of 33Mg is predominantly a combination of 32Mg(3.0 ,3.5 MeV ;2-,1-) ⨂νs1/2 , 32Mg(2.5 MeV ;2+) ⨂νp3/2 , and 32Mg(0 ;0+) ⨂νp3/2 . The experimentally obtained quantitative spectroscopic information for the valence neutron occupation of the s and p orbitals, coupled with different core states, is in agreement with Monte Carlo shell model (MCSM) calculation using 3 MeV as the shell gap at N =20 .
Morini, Filippo; Deleuze, Michael Simon; Watanabe, Noboru; Kojima, Masataka; Takahashi, Masahiko
2015-10-07
The influence of nuclear dynamics in the electronic ground state on the (e,2e) momentum profiles of dimethyl ether has been analyzed using the harmonic analytical quantum mechanical and Born-Oppenheimer molecular dynamics approaches. In spite of fundamental methodological differences, results obtained with both approaches consistently demonstrate that molecular vibrations in the electronic ground state have a most appreciable influence on the momentum profiles associated to the 2b{sub 1}, 6a{sub 1}, 4b{sub 2}, and 1a{sub 2} orbitals. Taking this influence into account considerably improves the agreement between theoretical and newly obtained experimental momentum profiles, with improved statistical accuracy. Both approaches point out in particular the most appreciable role which is played by a few specific molecular vibrations of A{sub 1}, B{sub 1}, and B{sub 2} symmetries, which correspond to C–H stretching and H–C–H bending modes. In line with the Herzberg-Teller principle, the influence of these molecular vibrations on the computed momentum profiles can be unraveled from considerations on the symmetry characteristics of orbitals and their energy spacing.
Static Properties and Stark Effect of the Ground State of the HD Molecular Ion
NASA Technical Reports Server (NTRS)
Bhatia, A. K.; Drachman, Richard J.
1999-01-01
We have calculated static properties of the ground state of the HD(+) ion and its lowest-lying P-state without making use of the Born-Oppenheimer approximation, as was done in the case of H2(+) and D2(+) [Phys. Rev. A 58, 2787 (1998)]. The ion is treated as a three-body system whose ground state is spherically symmetric. The wavefunction is of generalized Hylleraas type, but it is necessary to include high powers of the internuclear distance to localize the nuclear motion. We obtain good values of the energies of the ground S-state and lowest P-state and compare them with earlier calculations. Expectation values are obtained for various operators, the Fermi contact parameters, and the permanent quadrupole moment. The cusp conditions are also calculated. The polarizability was then calculated using second-order perturbation theory with intermediate P pseudostates. Since the nuclei in HD(+) are not of equal mass there is dipole coupling between the lowest two rotational states, which are almost degenerate. This situation is carefully analyzed, and the Stark shift is calculated variationally as a function of the applied electric field.
NASA Astrophysics Data System (ADS)
Morini, Filippo; Watanabe, Noboru; Kojima, Masataka; Deleuze, Michael Simon; Takahashi, Masahiko
2015-10-01
The influence of nuclear dynamics in the electronic ground state on the (e,2e) momentum profiles of dimethyl ether has been analyzed using the harmonic analytical quantum mechanical and Born-Oppenheimer molecular dynamics approaches. In spite of fundamental methodological differences, results obtained with both approaches consistently demonstrate that molecular vibrations in the electronic ground state have a most appreciable influence on the momentum profiles associated to the 2b1, 6a1, 4b2, and 1a2 orbitals. Taking this influence into account considerably improves the agreement between theoretical and newly obtained experimental momentum profiles, with improved statistical accuracy. Both approaches point out in particular the most appreciable role which is played by a few specific molecular vibrations of A1, B1, and B2 symmetries, which correspond to C-H stretching and H-C-H bending modes. In line with the Herzberg-Teller principle, the influence of these molecular vibrations on the computed momentum profiles can be unraveled from considerations on the symmetry characteristics of orbitals and their energy spacing.
Vexiau, R.; Lepers, M. Aymar, M.; Bouloufa-Maafa, N.; Dulieu, O.
2015-06-07
We have calculated the isotropic C{sub 6} coefficients characterizing the long-range van der Waals interaction between two identical heteronuclear alkali-metal diatomic molecules in the same arbitrary vibrational level of their ground electronic state X{sup 1}Σ{sup +}. We consider the ten species made up of {sup 7}Li, {sup 23}Na, {sup 39}K, {sup 87}Rb, and {sup 133}Cs. Following our previous work [Lepers et al., Phys. Rev. A 88, 032709 (2013)], we use the sum-over-state formula inherent to the second-order perturbation theory, composed of the contributions from the transitions within the ground state levels, from the transition between ground-state and excited state levels, and from a crossed term. These calculations involve a combination of experimental and quantum-chemical data for potential energy curves and transition dipole moments. We also investigate the case where the two molecules are in different vibrational levels and we show that the Moelwyn-Hughes approximation is valid provided that it is applied for each of the three contributions to the sum-over-state formula. Our results are particularly relevant in the context of inelastic and reactive collisions between ultracold bialkali molecules in deeply bound or in Feshbach levels.
Morini, Filippo; Watanabe, Noboru; Kojima, Masataka; Deleuze, Michael Simon; Takahashi, Masahiko
2015-10-01
The influence of nuclear dynamics in the electronic ground state on the (e,2e) momentum profiles of dimethyl ether has been analyzed using the harmonic analytical quantum mechanical and Born-Oppenheimer molecular dynamics approaches. In spite of fundamental methodological differences, results obtained with both approaches consistently demonstrate that molecular vibrations in the electronic ground state have a most appreciable influence on the momentum profiles associated to the 2b1, 6a1, 4b2, and 1a2 orbitals. Taking this influence into account considerably improves the agreement between theoretical and newly obtained experimental momentum profiles, with improved statistical accuracy. Both approaches point out in particular the most appreciable role which is played by a few specific molecular vibrations of A1, B1, and B2 symmetries, which correspond to C-H stretching and H-C-H bending modes. In line with the Herzberg-Teller principle, the influence of these molecular vibrations on the computed momentum profiles can be unraveled from considerations on the symmetry characteristics of orbitals and their energy spacing.
Majdi, Youssef; Hochlaf, Majdi; Pan, Yi; Lau, Kai-Chung; Poisson, Lionel; Garcia, Gustavo A; Nahon, Laurent; Al-Mogren, Muneerah Mogren; Schwell, Martin
2015-06-11
We report on the vibronic structure of the ground state X̃(2)A″ of the thymine cation, which has been measured using a threshold photoelectron photoion coincidence technique and vacuum ultraviolet synchrotron radiation. The threshold photoelectron spectrum, recorded over ∼0.7 eV above the ionization potential (i.e., covering the whole ground state of the cation) shows rich vibrational structure that has been assigned with the help of calculated anharmonic modes of the ground electronic cation state at the PBE0/aug-cc-pVDZ level of theory. The adiabatic ionization energy has been experimentally determined as AIE = 8.913 ± 0.005 eV, in very good agreement with previous high resolution results. The corresponding theoretical value of AIE = 8.917 eV has been calculated in this work with the explicitly correlated method/basis set (R)CCSD(T)-F12/cc-pVTZ-F12, which validates the theoretical approach and benchmarks its accuracy for future studies of medium-sized biological molecules.
Ground-state and dynamical properties of two-dimensional dipolar Fermi liquids
Abedinpour, Saeed H.; Asgari, Reza; Tanatar, B.; Polini, Marco
2014-01-15
We study the ground-state properties of a two-dimensional spin-polarized fluid of dipolar fermions within the Euler–Lagrange Fermi-hypernetted-chain approximation. Our method is based on the solution of a scattering Schrödinger equation for the “pair amplitude” √(g(r)), where g(r) is the pair distribution function. A key ingredient in our theory is the effective pair potential, which includes a bosonic term from Jastrow–Feenberg correlations and a fermionic contribution from kinetic energy and exchange, which is tailored to reproduce the Hartree–Fock limit at weak coupling. Very good agreement with recent results based on quantum Monte Carlo simulations is achieved over a wide range of coupling constants up to the liquid-to-crystal quantum phase transition. Using the fluctuation–dissipation theorem and a static approximation for the effective inter-particle interactions, we calculate the dynamical density–density response function, and furthermore demonstrate that an undamped zero-sound mode exists for any value of the interaction strength, down to infinitesimally weak couplings. -- Highlights: •We have studied the ground state properties of a strongly correlated two-dimensional fluid of dipolar fermions. •We have calculated the effective inter-particle interaction and the dynamical density–density response function. •We have shown that an undamped zero sound mode exists at any value of the interaction strength.
Structural anomalies and the orbital ground state in FeCr2S4
NASA Astrophysics Data System (ADS)
Tsurkan, V.; Zaharko, O.; Schrettle, F.; Kant, Ch.; Deisenhofer, J.; Krug von Nidda, H.-A.; Felea, V.; Lemmens, P.; Groza, J. R.; Quach, D. V.; Gozzo, F.; Loidl, A.
2010-05-01
We report on high-resolution x-ray synchrotron powder-diffraction, magnetic-susceptibility, sound-velocity, thermal-expansion, and heat-capacity studies of the stoichiometric spinel FeCr2S4 . We provide clear experimental evidence of a structural anomaly which accompanies an orbital-order transition at low temperatures due to a static cooperative Jahn-Teller effect. At 9 K, magnetic susceptibility, ultrasound velocity, and specific heat reveal pronounced anomalies that correlate with a volume contraction as evidenced by thermal-expansion data. The analysis of the low-temperature heat capacity using a mean-field model with a temperature-dependent gap yields a gap value of about 18 K and is interpreted as the splitting of the electronic ground state of Fe2+ by a cooperative Jahn-Teller effect. This value is close to the splitting of the ground state due to spin-orbit coupling for isolated Fe2+ ions in an insulating matrix, indicating that Jahn-Teller and spin-orbit coupling are competing energy scales in this system. We argue that due to this competition, the spin-reorientation transition at around 60 K marks the onset of short-range orbital ordering accompanied by a clear broadening of Bragg reflections, an enhanced volume contraction compared to usual anharmonic behavior, and a softening of the lattice observed in the ultrasound measurements.
Vos, M.; Marmitt, G. G.; Finkelstein, Y.; Moreh, R.
2015-09-14
Reflection electron energy loss spectra from some insulating materials (CaCO{sub 3}, Li{sub 2}CO{sub 3}, and SiO{sub 2}) taken at relatively high incoming electron energies (5–40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO{sub 2}, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E − E{sub gap}){sup 1.5}. For CaCO{sub 3}, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li{sub 2}CO{sub 3} (7.5 eV) is the first experimental estimate.
Vos, M; Marmitt, G G; Finkelstein, Y; Moreh, R
2015-09-14
Reflection electron energy loss spectra from some insulating materials (CaCO3, Li2CO3, and SiO2) taken at relatively high incoming electron energies (5-40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO2, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E - Egap)(1.5). For CaCO3, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li2CO3 (7.5 eV) is the first experimental estimate.
New Ground-State Crystal Structure of Elemental Boron.
An, Qi; Reddy, K Madhav; Xie, Kelvin Y; Hemker, Kevin J; Goddard, William A
2016-08-19
Elemental boron exhibits many polymorphs in nature based mostly on an icosahedral shell motif, involving stabilization of 13 strong multicenter intraicosahedral bonds. It is commonly accepted that the most thermodynamic stable structure of elemental boron at atmospheric pressure is the β rhombohedral boron (β-B). Surprisingly, using high-resolution transmission electron microscopy, we found that pure boron powder contains grains of two different types, the previously identified β-B containing a number of randomly spaced twins and what appears to be a fully transformed twinlike structure. This fully transformed structure, denoted here as τ-B, is based on the Cmcm orthorhombic space group. Quantum mechanics predicts that the newly identified τ-B structure is 13.8 meV/B more stable than β-B. The τ-B structure allows 6% more charge transfer from B_{57} units to nearby B_{12} units, making the net charge 6% closer to the ideal expected from Wade's rules. Thus, we predict the τ-B structure to be the ground state structure for elemental boron at atmospheric pressure. PMID:27588864
New Ground-State Crystal Structure of Elemental Boron
NASA Astrophysics Data System (ADS)
An, Qi; Reddy, K. Madhav; Xie, Kelvin Y.; Hemker, Kevin J.; Goddard, William A.
2016-08-01
Elemental boron exhibits many polymorphs in nature based mostly on an icosahedral shell motif, involving stabilization of 13 strong multicenter intraicosahedral bonds. It is commonly accepted that the most thermodynamic stable structure of elemental boron at atmospheric pressure is the β rhombohedral boron (β -B ). Surprisingly, using high-resolution transmission electron microscopy, we found that pure boron powder contains grains of two different types, the previously identified β -B containing a number of randomly spaced twins and what appears to be a fully transformed twinlike structure. This fully transformed structure, denoted here as τ -B , is based on the C m c m orthorhombic space group. Quantum mechanics predicts that the newly identified τ -B structure is 13.8 meV /B more stable than β -B . The τ -B structure allows 6% more charge transfer from B57 units to nearby B12 units, making the net charge 6% closer to the ideal expected from Wade's rules. Thus, we predict the τ -B structure to be the ground state structure for elemental boron at atmospheric pressure.
Antiferromagnetic ground state in NpCoGe
NASA Astrophysics Data System (ADS)
Colineau, E.; Griveau, J.-C.; Eloirdi, R.; Gaczyński, P.; Khmelevskyi, S.; Shick, A. B.; Caciuffo, R.
2014-03-01
NpCoGe, the neptunium analog of the ferromagnetic superconductor UCoGe, has been investigated by dc magnetization, ac susceptibility, specific heat, electrical resistivity, Hall effect, 237Np Mössbauer spectroscopy, and local spin-density approximation (LSDA) calculations. NpCoGe exhibits an antiferromagnetic ground state with a Néel temperature TN≈13 K and an average ordered magnetic moment <μNp>=0.80μB. The magnetic phase diagram has been determined and shows that the antiferromagnetic structure is destroyed by the application of a magnetic field (≈3 T). The value of the isomer shift suggests a Np3+ charge state (configuration 5f4). A high Sommerfeld coefficient value for NpCoGe (170 mJ mol-1 K-2) is inferred from specific heat. LSDA calculations indicate strong magnetic anisotropy and easy magnetization along the c axis. Mössbauer data and calculated exchange interactions support the possible occurrence of an elliptical spin-spiral structure in NpCoGe. The comparison with NpRhGe and uranium analogs suggests the leading role of 5f-d hybridization, the rather delocalized character of 5f electrons in NpCoGe, and the possible proximity of NpRuGe or NpFeGe to a magnetic quantum critical point.
Realization of Ground State Artificial Skyrmion Lattices at Room Temperature
NASA Astrophysics Data System (ADS)
Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew J.; Kirby, Brian J.; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Fischer, Peter; Liu, Kai
Artificial skyrmion lattices stable at ambient conditions offer a convenient and powerful platform to explore skyrmion physics and topological phenomena and motivates their inclusion in next-generation data and logic devices. In this work we present direct experimental evidence of artificial skyrmion lattices with a stable ground state at room temperature. Our approach is to pattern vortex-state Co nanodots (560 nm diameter) in hexagonal arrays on top of a Co/Pd multilayer with perpendicular magnetic anisotropy; the skyrmion state is prepared using a specific magnetic field sequence. Ion irradiation has been employed to suppress PMA in the underlayer and allow imprinting of the vortex structure from the nanodots to form skyrmion lattices, as revealed by polarized neutron reflectometry. Circularity control is realized through Co dot shape asymmetry, and confirmed by microscopy and FORC magnetometry. The vortex polarity is set during the field sequence and confirmed by magnetometry. Spin-transport studies further demonstrate a sensitivity to the skyrmion spin texture.Work supported by NSF (DMR-1008791, ECCS-1232275 and DMR-1543582)
Degenerate ground states and nonunique potentials: Breakdown and restoration of density functionals
Capelle, K.; Ullrich, C. A.; Vignale, G.
2007-07-15
The Hohenberg-Kohn (HK) theorem is one of the most fundamental theorems of quantum mechanics, and constitutes the basis for the very successful density-functional approach to inhomogeneous interacting many-particle systems. Here we show that in formulations of density-functional theory (DFT) that employ more than one density variable, applied to systems with a degenerate ground state, there is a subtle loophole in the HK theorem, as all mappings between densities, wave functions, and potentials can break down. Two weaker theorems which we prove here, the joint-degeneracy theorem and the internal-energy theorem, restore the internal, total, and exchange-correlation energy functionals to the extent needed in applications of DFT to atoms, molecules, and solids. The joint-degeneracy theorem constrains the nature of possible degeneracies in general many-body systems.
The ground state properties of spin-aligned atomic hydrogen, deuterium, and tritium
NASA Technical Reports Server (NTRS)
Etters, R. D.; Dugan, J. V., Jr.; Palmer, R. W.
1975-01-01
The internal energy, pressure, and compressibility of ground-state, spin-aligned atomic hydrogen, deuterium, and tritium are calculated assuming that all pair interactions occur via the atomic triplet (spin-aligned) potential. The conditions required to obtain atomic hydrogen and its isotopes in bulk are discussed; such a development would be of value in propulsion systems because of the light mass and energetic recombination of atomic hydrogen. Results show that atomic triplet hydrogen and deuterium remain gaseous at 0 K, and that tritium forms a liquid with a binding energy of approximately -0.75 K per atom at a molar volume of 130 cu cm per mole. The pair distribution function for these systems is calculated, and the predicted superfluid behavior of atomic triplet hydrogen and tritium is briefly discussed.
The 2p photoionization of ground-state sodium in the vicinity of Cooper minima
NASA Astrophysics Data System (ADS)
Liu, Xiaobin; Shi, Yinglong; Dong, Chenzhong
2016-07-01
The photoionization processes of ground-state sodium have been investigated with the multiconfiguration Dirac-Fock method. The results are in good or at least reasonable agreement with available experimental and theoretical data. In the energy region near the threshold, the cross sections show non-monotonic changes because of Cooper minima, which due to the sign changes of dominant dipole matrix elements and are very sensitive to electron correlations. As the energy increases continuously, the radial wave functions of the photoelectrons will move towards the nucleus. The values of the cross sections, and hence the Cooper minima, mainly depend on the relative positions of the one-electron radial wave functions of the initial bound electrons 2{p}1/{2,3/2} and the continuum photoelectrons.
Wang, Wenlong; Machta, Jonathan; Katzgraber, Helmut G
2015-07-01
Population annealing is a Monte Carlo algorithm that marries features from simulated-annealing and parallel-tempering Monte Carlo. As such, it is ideal to overcome large energy barriers in the free-energy landscape while minimizing a Hamiltonian. Thus, population-annealing Monte Carlo can be used as a heuristic to solve combinatorial optimization problems. We illustrate the capabilities of population-annealing Monte Carlo by computing ground states of the three-dimensional Ising spin glass with Gaussian disorder, while comparing to simulated-annealing and parallel-tempering Monte Carlo. Our results suggest that population annealing Monte Carlo is significantly more efficient than simulated annealing but comparable to parallel-tempering Monte Carlo for finding spin-glass ground states.
Sigman, M.E.; Autrey, T.; Schuster, G.B.
1988-06-22
The photochemistry of 4-acetylbenzoyl azide (ABA), 4-acetyl-4'-biphenoyl azide (ADA), and 4-acetylphenoxycarbonyl azide (APA) shows unusual wavelength and structural effects. Irradiation of ABA or ADA into their ..pi..-..pi..* bands with deep-UV light leads to formation of 4-acetylbenzoylnitrene (ABN) and 4-acetyl-4'-biphenoylnitrene (ADN), respectively, in competition with photo-Curtius rearrangement to form isocyanates. Irradiation of these azides into their n-..pi..* bands with near-UV light gives only the aroylnitrenes. The triplet excited states of the azides were detected chemically and by transient spectroscopic techniques. Nitrogen loss following near-UV irradiation occurs exclusively from the excited triplet azides. However, the chemical properties of ABN and ADN are consistent only with reactions originating from their singlet states. An ESR spectrum is observed at 8 K for ((4-acetylphenoxy)carbonyl) nitrene (APN) but not for 4-acetylbenzoylnitrene (ABN) or 4-acetyl-4'-biphenylcarbonylnitrene (ADN). The chemical properties of APN in tert-butyl alcohol show that its triplet is no more than 5 kcal/mol below its lowest single state. In contrast, the chemical properties of ABN and ADN indicate that these nitrenes have singlet ground states.
Threshold conditions, energy spectrum and bands generated by locally periodic Dirac comb potentials
NASA Astrophysics Data System (ADS)
Dharani, M.; Shastry, C. S.
2016-01-01
We derive expressions for polynomials governing the threshold conditions for different types of locally periodic Dirac comb potentials comprising of attractive and combination of attractive and repulsive delta potential terms confined symmetrically inside a one dimensional box of fixed length. The roots of these polynomials specify the conditions on the potential parameters in order to generate threshold energy bound states. The mathematical and numerical methods used by us were first formulated in our earlier works and it is also very briefly summarized in this paper. We report a number of mathematical results pertaining to the threshold conditions and these are useful in controlling the number of negative energy states as desired. We further demonstrate the correlation between the distribution of roots of these polynomials and negative energy eigenvalues. Using these results as basis, we investigate the energy bands in the positive energy spectrum for the above specified Dirac comb potentials and also for the corresponding repulsive case. In the case of attractive Dirac comb the base energy of the each band excluding the first band coincides with specific eigenvalue of the confining box whereas in the repulsive case it coincides with the band top. We deduce systematic correlation between band gaps, band spreads and box eigenvalues and explain the physical reason for the vanishing of band pattern at higher energies. In the case of Dirac comb comprising of orderly arranged attractive and repulsive delta potentials, specific box eigenvalues occur in the middle of each band excluding the first band. From our study we find that by controlling the number and strength parameters of delta terms in the Dirac comb and the size of confining box it is possible to generate desired types of band formations. We believe the results from our systematic analysis are useful and relevant in the study of various one dimensional systems of physical interest in areas like nanoscience.
Novel, discontinuous polaron transition in a two-band model
NASA Astrophysics Data System (ADS)
Moeller, Mirko M.; Sawatzky, George A.; Berciu, Mona
The coupling of charge carriers (electrons or holes) to phonons leads to the formation of a polaron, a coherent quasi-particle consisting of the charge carrier and the cloud of phonons surrounding it and moving coherently with it. Here we present exact diagonalization and momentum average approximation results for the single polaron properties of a two-band model with phonon modulated hopping, inspired by the perovskite BaBiO3. For large coupling we find that the ground state momentum changes discontinuously from k = π to k = 0 . Such sharp transitions of the polaron's ground state properties cannot occur in the well-studied models of the Holstein or Fröhlich type in which the carrier-phonon coupling modulates the on-site energies. However, they can occur in models where the carrier-phonon coupling modulates the hopping integrals such as the SSH model for which a similar yet smooth transition of the ground state momentum was recently shown to exist. We compare our findings to the SSH model and point out qualitative differences which we believe to be due to the two band nature of our model versus the single band SSH model. This work was supported by NSERC, QMI and the UBC 4YF.
Energy loss of ions at metal surfaces: Band-structure effects
Alducin, M.; Silkin, V.M.; Juaristi, J.I.; Chulkov, E.V.
2003-03-01
We study band-structure effects on the energy loss of protons scattered off the Cu (111) surface. The distance dependent stopping power for a projectile traveling parallel to the surface is calculated within the linear response theory. The self-consistent electronic response of the system is evaluated within the random-phase approximation. In order to characterize the surface band structure, the electronic single-particle wave functions and energies are obtained by solving the Schroedinger equation with a realistic one-dimensional model potential. This potential reproduces the main features of the Cu (111) surface: the energy band gap for electron motion along the surface normal, as well as the binding energy of the occupied surface state and the first image state. Comparison of our results with those obtained within the jellium model allows us to characterize the band-structure effects in the energy loss of protons interacting with the Cu (111) surface.
Clark, Aurora E; Davidson, Ernest R
2003-05-01
In an effort to find a p-benzyne (1,4-didehydrobenzene) derivative with a triplet ground state, we have investigated tetrasubstitution by -F, -NH(2), -CH(3), and -NO(2) groups. These were predicted to reduce the singlet-triplet gap, but none led to a triplet ground state because of unexpected destabilization of one of the radical orbitals. This effect is likely the result of rehybridization of the substituted C atom, which has been observed for substituted benzene and perturbs the side sigma and sigma* orbital energies of the phenyl ring. The role of substituent rotation on the energy difference between the two nominally singly occupied orbitals (S and A) was then investigated. The energy of the A radical orbital was found to be much more sensitive to perturbations within the sigma C[bond]C framework than the S MO. Consequently, we believe that rehybridization of the ring carbons destabilizes the A radical orbital and can lead to large singlet-triplet splittings. To test this hypothesis, calculations on a p-benzyne with 2,6 substitution by oxygen were performed. Interestingly, a triplet ground state was predicted. Yet, examination of the geometry and wave function showed that 2,6-quinone p-benzyne is a very twisted molecule with a C3-C4-C5 allene linkage and a C1 triplet carbene center.
NASA Astrophysics Data System (ADS)
Hu, Ji-Hong; Wang, Jing-Jing; Xianlong, Gao; Okumura, Masahiko; Igarashi, Ryo; Yamada, Susumu; Machida, Masahiko
2010-07-01
We revisit the one-dimensional attractive Hubbard model by using the Bethe-ansatz-based density-functional theory and density-matrix renormalization method. The ground-state properties of this model are discussed in details for different fillings and different confining conditions in weak-to-intermediate coupling regime. We investigate the ground-state energy, energy gap, and pair-binding energy and compare them with those calculated from the canonical Bardeen-Cooper-Schrieffer approximation. We find that the Bethe-ansatz-based density-functional theory is computationally easy and yields an accurate description of the ground-state properties for weak-to-intermediate interaction strength, different fillings, and confinements. In order to characterize the quantum phase transition in the presence of a harmonic confinement, we calculate the thermodynamic stiffness, the density-functional fidelity, and fidelity susceptibility, respectively. It is shown that with the increase in the number of particles or attractive interaction strength, the system can be driven from the Luther-Emery-type phase to the composite phase of Luther-Emery-type in the wings and insulatinglike in the center.
Anisotropy of the high-energy satellites of the K emission band in graphite
NASA Astrophysics Data System (ADS)
Mansour, A.; Schnatterly, S. E.; Carson, R. D.
1985-05-01
Two satellites on the high-energy side of the K emission band of graphite have been observed and found to be anisotropic. One of them is attributed to the radiative decay of double ionization of the K shell while the other is tentatively explained as resulting from electronic transitions from the conduction-band minimum into the K-shell vacancy.
Ground state of bilayer hα-silica: mechanical and electronic properties
NASA Astrophysics Data System (ADS)
Han, Yang; Hu, Ming
2015-12-01
The family of two-dimensional (2D) crystals was recently joined by silica, one of the most abundant resources on earth. So far two different polymorphs of this material, namely a tetrahedra-shaped monolayer and a fully saturated bilayer structure, have been synthesized on various metal substrates and their fascinating properties enable 2D silica to hold promise in nanoelectronic device applications. In this paper a new ground state of bilayer—AAr-stacking hα-silica—has been discovered by first principles calculations. The new structure is featured with a formation of Si-Si bonds between all sp3 hybridized SiO3 triangular pyramids, lying respectively in different silica layers, with an intrinsic rotational angle of about 12.5° along the out-of-plane Si-Si bond. Due to the doubled number of Si-Si bonds in the new structure, the system energy is lowered by nearly three times more than that reported recently in literature (0.8 eV) (Özçelik et al 2014 Phys. Rev. Lett. 112 246803), when compared with the single layer hα-silica. A mechanical property investigation shows that the AAr-stacking bilayer hα-silica possesses high in-plane stiffness and a negative Poisson’s ratio, which stems from the intrinsic rotational angle of the SiO3 triangular pyramids. Strikingly, the negative Poisson’s ratio evolves into positive at a critical tensile strain ɛ ≈ 1.2%. Such negative-to-positive evolvement is associated with the adaptation of the rotational angle to the applied strain and the structure transition into the nearby valley of the energy landscape. The detailed transition process has been thoroughly analyzed. The electronic properties of the new ground state are also calculated, along with their response to the external strain. Our new ground state structure introduces a new member to the family of 2D bilayer silica materials and is expected to facilitate experimental studies identifying the related structures and exploring further physical and chemical
Energy Dependence and Scaling Property of Localization Length near a Gapped Flat Band
NASA Astrophysics Data System (ADS)
Ge, Li; Tureci, Hakan
Using a tight-binding model for a one-dimensional Lieb lattice, we show that the localization length near a gapped flat band behaves differently from the typical Urbach tail in a band gap: instead of reducing monotonically as the energy E moves away from the flat band energy Ef, the presence of the flat band causes a nonmonotonic energy dependence of the localization length. This energy dependence follows a scaling property when the energy is within the spread (W) of uniformly distributed diagonal disorder, i.e. the localization length is only a function of (E-Ef)/W. Several other lattices are compared to distinguish the effect of the flat band on the localization length, where we eliminate, shift, or duplicate the flat band, without changing the dispersion relations of other bands. Using the top right element of the Green's matrix, we derive an analytical relation between the density of states and the localization length, which shines light on these properties of the latter, including a summation rule for its inverse. This work is partially supported by NSF under Grant No. DMR-1506987.
A new two-parameter family of potentials with a tunable ground state
NASA Astrophysics Data System (ADS)
Fellows, Jonathan M.; Smith, Robert A.
2011-08-01
In a previous paper (Fellows and Smith 2009 J. Phys. A: Math. Theor. 42 335303) we solved a countably infinite family of one-dimensional Schrödinger equations by showing that they were supersymmetric partner potentials of the standard quantum harmonic oscillator. In this work we extend these results to find the complete set of real partner potentials of the harmonic oscillator, showing that these depend upon two continuous parameters. Their spectra are identical to that of the harmonic oscillator, except that the ground state energy becomes a tunable parameter. We finally use these potentials to analyse the physical problem of Bose-Einstein condensation in an atomic gas trapped in a dimple potential.
Classical ground states of Heisenberg and X Y antiferromagnets on the windmill lattice
NASA Astrophysics Data System (ADS)
Jeevanesan, Bhilahari; Orth, Peter P.
2014-10-01
We investigate the classical Heisenberg and planar (X Y ) spin models on the windmill lattice. The windmill lattice is formed out of two widely occurring lattice geometries: a triangular lattice is coupled to its dual honeycomb lattice. Using a combination of iterative minimization, heat-bath Monte Carlo simulations, and analytical calculations, we determine the complete ground-state phase diagram of both models and find the exact energies of the phases. The phase diagram shows a rich phenomenology due to competing interactions and hosts, in addition to collinear and various coplanar phases, also intricate noncoplanar phases. We briefly outline different paths to an experimental realization of these spin models. Our extensive study provides a starting point for the investigation of quantum and thermal fluctuation effects.
Ground-State Chemical Reactivity under Vibrational Coupling to the Vacuum Electromagnetic Field.
Thomas, Anoop; George, Jino; Shalabney, Atef; Dryzhakov, Marian; Varma, Sreejith J; Moran, Joseph; Chervy, Thibault; Zhong, Xiaolan; Devaux, Eloïse; Genet, Cyriaque; Hutchison, James A; Ebbesen, Thomas W
2016-09-12
The ground-state deprotection of a simple alkynylsilane is studied under vibrational strong coupling to the zero-point fluctuations, or vacuum electromagnetic field, of a resonant IR microfluidic cavity. The reaction rate decreased by a factor of up to 5.5 when the Si-C vibrational stretching modes of the reactant were strongly coupled. The relative change in the reaction rate under strong coupling depends on the Rabi splitting energy. Product analysis by GC-MS confirmed the kinetic results. Temperature dependence shows that the activation enthalpy and entropy change significantly, suggesting that the transition state is modified from an associative to a dissociative type. These findings show that vibrational strong coupling provides a powerful approach for modifying and controlling chemical landscapes and for understanding reaction mechanisms. PMID:27529831
Beg, Marijan; Carey, Rebecca; Wang, Weiwei; Cortés-Ortuño, David; Vousden, Mark; Bisotti, Marc-Antonio; Albert, Maximilian; Chernyshenko, Dmitri; Hovorka, Ondrej; Stamps, Robert L.; Fangohr, Hans
2015-01-01
Magnetic skyrmions have the potential to provide solutions for low-power, high-density data storage and processing. One of the major challenges in developing skyrmion-based devices is the skyrmions’ magnetic stability in confined helimagnetic nanostructures. Through a systematic study of equilibrium states, using a full three-dimensional micromagnetic model including demagnetisation effects, we demonstrate that skyrmionic textures are the lowest energy states in helimagnetic thin film nanostructures at zero external magnetic field and in absence of magnetocrystalline anisotropy. We also report the regions of metastability for non-ground state equilibrium configurations. We show that bistable skyrmionic textures undergo hysteretic behaviour between two energetically equivalent skyrmionic states with different core orientation, even in absence of both magnetocrystalline and demagnetisation-based shape anisotropies, suggesting the existence of Dzyaloshinskii-Moriya-based shape anisotropy. Finally, we show that the skyrmionic texture core reversal dynamics is facilitated by the Bloch point occurrence and propagation. PMID:26601904
Quantum Monte Carlo Study of the Ground-State Properties of a Fermi Gas in the BCS-BEC Crossover
Giorgini, S.; Astrakharchik, G. E.; Boronat, J.; Casulleras, J.
2006-11-07
The ground-state properties of a two-component Fermi gas with attractive short-range interactions are calculated using the fixed-node diffusion Monte Carlo method. The interaction strength is varied over a wide range by tuning the value of the s-wave scattering length of the two-body potential. We calculate the ground-state energy per particle and we characterize the equation of state of the system. Off-diagonal long-range order is investigated through the asymptotic behavior of the two-body density matrix. The condensate fraction of pairs is calculated in the unitary limit and on both sides of the BCS-BEC crossover.
NASA Technical Reports Server (NTRS)
Drachman, Richard J.
2006-01-01
Formation of triplet positron-helium bound state by stripping of positronium atoms in collision with ground state helium JOSEPH DI RlENZI, College of Notre Dame of Maryland, RICHARD J. DRACHMAN, NASA/Goddard Space Flight Center - The system consisting of a positron and a helium atom in the triplet state e(+)He(S-3)(sup e) was conjectured long ago to be stable [1]. Its stability has recently been established rigorously [2], and the values of the energies of dissociation into the ground states of Ps and He(+) have also been reported [3] and [4]. We have evaluated the cross-section for this system formed by radiative attachment of a positron in triplet He state and found it to be small [5]. The mechanism of production suggested here should result in a larger cross-section (of atomic size) which we are determining using the Born approximation with simplified initial and final wave functions.
The 75As(n,2n) Cross Sections into the 74As Isomer and Ground State
Younes, W; Garrett, P E; Becker, J A; Bernstein, L A; Ormand, W E; Dietrich, F S; Nelson, R O; Devlin, M; Fotiades, N
2003-06-30
The {sup 75}As(n, 2n) cross section for the population of the T{sub 1/2} = 26.8-ns isomer at E{sub x} = 259.3 keV in {sup 74}As has been measured as a function of incident neutron energy, from threshold to E{sub n} = 20 MeV. The cross section was measured using the GEANIE spectrometer at LANSCE/WNR. For convenience, the {sup 75}As(n, 2n) population cross section for the {sup 74}As ground state has been deduced as the difference between the previously-known (n, 2n) reaction cross section and the newly measured {sup 75}As(n, 2n){sup 74}As{sup m} cross section. The (n, 2n) reaction, ground-state, and isomer population cross sections are tabulated in this paper.
NASA Astrophysics Data System (ADS)
Dai, Xing; Gao, Yang; Xin, Minsi; Wang, Zhigang; Zhou, Ruhong
2014-12-01
As a representative lanthanide endohedral metallofullerene, Gd@C82 has attracted a widespread attention among theorists and experimentalists ever since its first synthesis. Through comprehensive comparisons and discussions, as well as references to the latest high precision experiments, we evaluated the performance of different computational methods. Our results showed that the appropriate choice of the exchange-correlation functionals is the decisive factor to accurately predict both geometric and electronic structures for Gd@C82. The electronic structure of the ground state and energy gap between the septet ground state and the nonet low-lying state obtained from pure density functional methods, such as PBE and PW91, are in good agreement with current experiment. Unlike pure functionals, the popularly used hybrid functionals in previous studies, such as B3LYP, could infer the qualitative correct ground state only when small basis set for C atoms is employed. Furthermore, we also highlighted that other geometric structures of Gd@C82 with the Gd staying at different positions are either not stable or with higher energies. This work should provide some useful references for various theoretical methodologies in further density functional studies on Gd@C82 and its derivatives in the future.
First-principle study of energy band structure of armchair graphene nanoribbons
NASA Astrophysics Data System (ADS)
Ma, Fei; Guo, Zhankui; Xu, Kewei; Chu, Paul K.
2012-07-01
First-principle calculation is carried out to study the energy band structure of armchair graphene nanoribbons (AGNRs). Hydrogen passivation is found to be crucial to convert the indirect band gaps into direct ones as a result of enhanced interactions between electrons and nuclei at the edge boundaries, as evidenced from the shortened bond length as well as the increased differential charge density. Ribbon width usually leads to the oscillatory variation of band gaps due to quantum confinement no matter hydrogen passivated or not. Mechanical strain may change the crystal symmetry, reduce the overlapping integral of C-C atoms, and hence modify the band gap further, which depends on the specific ribbon width sensitively. In practical applications, those effects will be hybridized to determine the energy band structure and subsequently the electronic properties of graphene. The results can provide insights into the design of carbon-based devices.
NASA Astrophysics Data System (ADS)
Freitas, F. L.; Marques, M.; Teles, L. K.
2016-08-01
We provide approximate quasiparticle-corrected band gap energies for quaternary cubic and hexagonal AlxGayIn1-x-yN semiconductor alloys, employing a cluster expansion method to account for the inherent statistical disorder of the system. Calculated values are compared with photoluminescence measurements and discussed within the currently accepted model of emission in these materials by carrier localization. It is shown that bowing parameters are larger in the cubic phase, while the range of band gap variation is bigger in the hexagonal one. Experimentally determined transition energies are mostly consistent with band-to-band excitations.
Observation of γ-vibrations and alignments built on non-ground-state configurations in ¹⁵⁶Dy
Zhu, C. -H.; Hartley, D. J.; Riedinger, L. L.; Sharpey-Schafer, J. F.; Almond, J. M.; Beausang, C.; Carpenter, M. P.; Chiara, C. J.; Cooper, N.; Curien, D.; Gall, B. J. P.; Garrett, P. E.; Janssens, R. V. F.; Kondev, F. G.; Kulp, W. D.; Lauritsen, T.; McCutchan, E. A.; Miller, D.; Piot, J.; Redon, N.; Riley, M. A.; Simpson, J.; Stefanescu, I.; Werner, V.; Wang, X.; Wood, J. L.; Majola, S. N. T.; Zhu, S.
2015-03-26
The exact nature of the lowest K^{π}=2⁺ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the γ degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ-bands have been traced past the usual back-bending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus ¹⁵⁶Dy, using the ¹⁴⁸Nd(¹²C,4n)¹⁵⁶Dy reaction at 65 MeV, observing the resulting γ-ray transitions with the Gammasphere array. The even- and odd-spin members of the ^{π}=2⁺ γ-band are observed to 32⁺ and 31⁺ respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ-vibration built on the aligned yrast S-band are observed to spins 28⁺ and 27⁺. An even-spin positive-parity band, observed to spin 24⁺, is a candidate for an aligned S-band built on the seniority-zero configuration of the 0₂⁺ state at 676 keV. As a result, the crossing of this band with the 0₂⁺ band is at hw_{c} = 0.28(1) MeV and is consistent with the configuration of the 0₂⁺ band not producing any blocking of the monopole pairing.
Observation of γ-vibrations and alignments built on non-ground-state configurations in ¹⁵⁶Dy
Zhu, C. -H.; Hartley, D. J.; Riedinger, L. L.; Sharpey-Schafer, J. F.; Almond, J. M.; Beausang, C.; Carpenter, M. P.; Chiara, C. J.; Cooper, N.; Curien, D.; et al
2015-03-26
The exact nature of the lowest Kπ=2⁺ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the γ degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ-bands have been traced past the usual back-bending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus ¹⁵⁶Dy, using the ¹⁴⁸Nd(¹²C,4n)¹⁵⁶Dy reaction at 65 MeV, observing the resulting γ-ray transitions with the Gammasphere array. The even- and odd-spin members of the π=2⁺ γ-band are observed to 32⁺ and 31⁺ respectively.more » This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ-vibration built on the aligned yrast S-band are observed to spins 28⁺ and 27⁺. An even-spin positive-parity band, observed to spin 24⁺, is a candidate for an aligned S-band built on the seniority-zero configuration of the 0₂⁺ state at 676 keV. As a result, the crossing of this band with the 0₂⁺ band is at hwc = 0.28(1) MeV and is consistent with the configuration of the 0₂⁺ band not producing any blocking of the monopole pairing.« less
Derivation of novel human ground state naive pluripotent stem cells.
Gafni, Ohad; Weinberger, Leehee; Mansour, Abed AlFatah; Manor, Yair S; Chomsky, Elad; Ben-Yosef, Dalit; Kalma, Yael; Viukov, Sergey; Maza, Itay; Zviran, Asaf; Rais, Yoach; Shipony, Zohar; Mukamel, Zohar; Krupalnik, Vladislav; Zerbib, Mirie; Geula, Shay; Caspi, Inbal; Schneir, Dan; Shwartz, Tamar; Gilad, Shlomit; Amann-Zalcenstein, Daniela; Benjamin, Sima; Amit, Ido; Tanay, Amos; Massarwa, Rada; Novershtern, Noa; Hanna, Jacob H
2013-12-12
Mouse embryonic stem (ES) cells are isolated from the inner cell mass of blastocysts, and can be preserved in vitro in a naive inner-cell-mass-like configuration by providing exogenous stimulation with leukaemia inhibitory factor (LIF) and small molecule inhibition of ERK1/ERK2 and GSK3β signalling (termed 2i/LIF conditions). Hallmarks of naive pluripotency include driving Oct4 (also known as Pou5f1) transcription by its distal enhancer, retaining a pre-inactivation X chromosome state, and global reduction in DNA methylation and in H3K27me3 repressive chromatin mark deposition on developmental regulatory gene promoters. Upon withdrawal of 2i/LIF, naive mouse ES cells can drift towards a primed pluripotent state resembling that of the post-implantation epiblast. Although human ES cells share several molecular features with naive mouse ES cells, they also share a variety of epigenetic properties with primed murine epiblast stem cells (EpiSCs). These include predominant use of the proximal enhancer element to maintain OCT4 expression, pronounced tendency for X chromosome inactivation in most female human ES cells, increase in DNA methylation and prominent deposition of H3K27me3 and bivalent domain acquisition on lineage regulatory genes. The feasibility of establishing human ground state naive pluripotency in vitro with equivalent molecular and functional features to those characterized in mouse ES cells remains to be defined. Here we establish defined conditions that facilitate the derivation of genetically unmodified human naive pluripotent stem cells from already established primed human ES cells, from somatic cells through induced pluripotent stem (iPS) cell reprogramming or directly from blastocysts. The novel naive pluripotent cells validated herein retain molecular characteristics and functional properties that are highly similar to mouse naive ES cells, and distinct from conventional primed human pluripotent cells. This includes competence in the generation
Electronic ground state properties of Coulomb blockaded quantum dots
NASA Astrophysics Data System (ADS)
Patel, Satyadev Rajesh
Conductance through quantum dots at low temperature exhibits random but repeatable fluctuations arising from quantum interference of electrons. The observed fluctuations follow universal statistics arising from the underlying universality of quantum chaos. Random matrix theory (RMT) has provided an accurate description of the observed universal conductance fluctuations (UCF) in "open" quantum dots (device conductance ≥e 2/h). The focus of this thesis is to search for and decipher the underlying origin of similar universal properties in "closed" quantum dots (device conductance ≤e2/ h). A series of experiments is presented on electronic ground state properties measured via conductance measurements in Coulomb blockaded quantum dots. The statistics of Coulomb blockade (CB) peak heights with zero and non-zero magnetic field measured in various devices agree qualitatively with predictions from Random Matrix Theory (RMT). The standard deviation of the peak height fluctuations for non-zero magnetic field is lower than predicted by RMT; the temperature dependence of the standard deviation of the peak height for non-zero magnetic field is also measured. The second experiment summarizes the statistics of CB peak spacings. The peak spacing distribution width is observed to be on the order of the single particle level spacing, Delta, for both zero and non-zero magnetic field. The ratio of the zero field peak spacing distribution width to the non-zero field peak spacing distribution width is ˜1.2; this is good agreement with predictions from spin-resolved RMT predictions. The standard deviation of the non-zero magnetic field peak spacing distribution width shows a T-1/2 dependence in agreement with a thermal averaging model. The final experiment summarizes the measurement of the peak height correlation length versus temperature for various quantum dots. The peak height correlation length versus temperature saturates in small quantum dots, suggesting spectral scrambling
Lin, Tai-Chia; Belić, Milivoj R.; Petrović, Milan S.; Chen, Goong
2014-01-15
Counterpropagating optical beams in nonlinear media give rise to a host of interesting nonlinear phenomena such as the formation of spatial solitons, spatiotemporal instabilities, self-focusing and self-trapping, etc. Here we study the existence of ground state (the energy minimizer under the L{sup 2}-normalization condition) in two-dimensional (2D) nonlinear Schrödinger (NLS) systems with saturable nonlinearity, which describes paraxial counterpropagating beams in isotropic local media. The nonlinear coefficient of saturable nonlinearity exhibits a threshold which is crucial in determining whether the ground state exists. The threshold can be estimated by the Gagliardo-Nirenberg inequality and the ground state existence can be proved by the energy method, but not the concentration-compactness method. Our results also show the essential difference between 2D NLS equations with cubic and saturable nonlinearities.
NASA Astrophysics Data System (ADS)
Kohley, Z.; Spyrou, A.; Lunderberg, E.; DeYoung, P. A.; Attanayake, H.; Baumann, T.; Bazin, D.; Brown, B. A.; Christian, G.; Divaratne, D.; Grimes, S. M.; Haagsma, A.; Finck, J. E.; Frank, N.; Luther, B.; Mosby, S.; Nagi, T.; Peaslee, G. F.; Peters, W. A.; Schiller, A.; Smith, J. K.; Snyder, J.; Strongman, M. J.; Thoennessen, M.; Volya, A.
2013-03-01
The two-neutron unbound ground state resonances of 26O and 16Be were populated using one-proton knockout reactions from 27F and 17B beams. A coincidence measurement of 3-body system (fragment + n + n) allowed for the decay energy of the unbound nuclei to be reconstructed. A low energy resonance, < 200 keV, was observed for the first time in the 240 + n + n system and assigned to the ground state of 26O. The 16Be ground state resonance was observed at 1.35 MeV. The 3-body correlations of the 14Be + n + n system were compared to simulations of a phase-space, sequential, and dineutron decay. The strong correlations in the n-n system from the experimental data could only be reproduced by the dineutron decay simulation providing the first evidence for a dineutron-like decay.
Improved cache performance in Monte Carlo transport calculations using energy banding
NASA Astrophysics Data System (ADS)
Siegel, A.; Smith, K.; Felker, K.; Romano, P.; Forget, B.; Beckman, P.
2014-04-01
We present an energy banding algorithm for Monte Carlo (MC) neutral particle transport simulations which depend on large cross section lookup tables. In MC codes, read-only cross section data tables are accessed frequently, exhibit poor locality, and are typically too much large to fit in fast memory. Thus, performance is often limited by long latencies to RAM, or by off-node communication latencies when the data footprint is very large and must be decomposed on a distributed memory machine. The proposed energy banding algorithm allows maximal temporal reuse of data in band sizes that can flexibly accommodate different architectural features. The energy banding algorithm is general and has a number of benefits compared to the traditional approach. In the present analysis we explore its potential to achieve improvements in time-to-solution on modern cache-based architectures.
Accurate ab initio calculations which demonstrate a 3 Pi u ground state for Al2
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R.; Taylor, Peter R.; Walch, Stephen P.
1986-01-01
The spectroscopic parameters and separations between the three low-lying X 3 Pi u, A 3 Sigma g -, and a 1 Sigma g + states of Al2 are studied as a function of both the one-particle and n-particle basis set. Approximate correlation treatments are calibrated against full Cl calculations correlating the six valence electrons in a double-zeta plus two d-function basis set. Since the CASSCF/MRCI 3 Pi u to 3 Sigma g - separation is in excellent agreement wtih the FCI value, the MRCI calculations were carried out in an extended (20s13p6d4f)/(6s5p3d2f) gaussian basis. Including a small correction for relativistic effects, the best estimate is that 3 Sigma g - state lies 174/cm above the 3 Pi u ground state. The 1 Sigma g + state lies at least 2000/cm higher in energy. At the CPF level, inclusion of 2s and 2p correlation has little effect on D sub e, reduces T sub e by only 26/cm, and shortens the bond lengths by about 0.02 a sub o. Further strong support for a 3 Pi u ground state comes from the experimental absorption spectra, since both observed transitions can be convincingly assigned as 3 Pi u yields 3 Pi g. The (2) 3 Pi g state is observed to be sensitive to the level of correlation treatment, and to have its minimum shifted to shorter rho values, such that the strongest experimental absorption peak probably corresponds to the 0 yields 2 transition.
Zhang, Tianyuan; Evangelista, Francesco A
2016-09-13
In this work we propose a novel approach to solve the Schrödinger equation which combines projection onto the ground state with a path-filtering truncation scheme. The resulting projector configuration interaction (PCI) approach realizes a deterministic version of the full configuration interaction quantum Monte Carlo (FCIQMC) method [Booth, G. H.; Thom, A. J. W.; Alavi, A. J. Chem. Phys. 2009, 131, 054106]. To improve upon the linearized imaginary-time propagator, we develop an optimal projector scheme based on an exponential Chebyshev expansion in the limit of an infinite imaginary time step. After writing the exact projector as a path integral in determinant space, we introduce a path filtering procedure that truncates the size of the determinantal basis and approximates the Hamiltonian. The path filtering procedure is controlled by one real threshold that determines the accuracy of the PCI energy and is not biased toward any determinant. Therefore, the PCI approach can equally well describe static and dynamic electron correlation effects. This point is illustrated in benchmark computations on N2 at both equilibrium and stretched geometries. In both cases, the PCI achieves chemical accuracy with wave functions that contain less than 0.5% determinants of full CI space. We also report computations on the ground state of C2 with up to quaduple-ζ basis sets and wave functions as large as 200 million determinants, which allow a direct comparison of the PCI, FCIQMC, and density matrix renormalization group (DMRG) methods. The size of the PCI wave function grows modestly with the number of unoccupied orbitals, and its accuracy may be tuned to match that of FCIQMC and DMRG. PMID:27464301
An electric field tunable energy band gap at silicene/(0001) ZnS interfaces.
Houssa, M; van den Broek, B; Scalise, E; Pourtois, G; Afanas'ev, V V; Stesmans, A
2013-03-21
The interaction of silicene, the silicon counterpart of graphene, with (0001) ZnS surfaces is investigated theoretically, using first-principles simulations. The charge transfer occurring at the silicene/(0001) ZnS interface leads to the opening of an indirect energy band gap of about 0.7 eV in silicene. Remarkably, the nature (indirect or direct) and magnitude of the energy band gap of silicene can be controlled by an external electric field: the energy gap is predicted to become direct for electric fields larger than about 0.5 V Å(-1), and the direct energy gap decreases approximately linearly with the applied electric field. The predicted electric field tunable energy band gap of the silicene/(0001) ZnS interface is very promising for its potential use in nanoelectronic devices.
Graph states as ground states of two-body frustration-free Hamiltonians
NASA Astrophysics Data System (ADS)
Darmawan, Andrew S.; Bartlett, Stephen D.
2014-07-01
The framework of measurement-based quantum computation (MBQC) allows us to view the ground states of local Hamiltonians as potential resources for universal quantum computation. A central goal in this field is to find models with ground states that are universal for MBQC and that are also natural in the sense that they involve only two-body interactions and have a small local Hilbert space dimension. Graph states are the original resource states for MBQC, and while it is not possible to obtain graph states as exact ground states of two-body Hamiltonians, here we construct two-body frustration-free Hamiltonians that have arbitrarily good approximations of graph states as unique ground states. The construction involves taking a two-body frustration-free model that has a ground state convertible to a graph state with stochastic local operations, then deforming the model such that its ground state is close to a graph state. Each graph state qubit resides in a subspace of a higher dimensional particle. This deformation can be applied to two-body frustration-free Affleck-Kennedy-Lieb-Tasaki (AKLT) models, yielding Hamiltonians that are exactly solvable with exact tensor network expressions for ground states. For the star-lattice AKLT model, the ground state of which is not expected to be a universal resource for MBQC, applying such a deformation appears to enhance the computational power of the ground state, promoting it to a universal resource for MBQC. Transitions in computational power, similar to percolation phase transitions, can be observed when Hamiltonians are deformed in this way. Improving the fidelity of the ground state comes at the cost of a shrinking gap. While analytically proving gap properties for these types of models is difficult in general, we provide a detailed analysis of the deformation of a spin-1 AKLT state to a linear graph state.
Energy band bowing parameter in MgZnO alloys
Wang, Xu; Saito, Katsuhiko; Tanaka, Tooru; Nishio, Mitsuhiro; Guo, Qixin; Nagaoka, Takashi; Arita, Makoto
2015-07-13
We report on bandgap bowing parameters for wurtzite and cubic MgZnO alloys from a study of high quality and single phase films in all Mg content range. The Mg contents in the MgZnO films were accurately determined using the energy dispersive spectrometer and X-ray photoelectron spectroscopy (XPS). The measurement of bandgap energies by examining the onset of inelastic energy loss in core-level atomic spectra from XPS is proved to be valid for determining the bandgap of MgZnO films. The dependence of the energy bandgap on Mg content is found to deviate downwards from linearity. Fitting of the bandgap data resulted in two bowing parameters of 2.01 ± 0.04 eV and 1.48 ± 0.11 eV corresponding to wurtzite and cubic MgZnO films, respectively.
Prediction of a new ground state of superhard compound B6O at ambient conditions.
Dong, Huafeng; Oganov, Artem R; Wang, Qinggao; Wang, Sheng-Nan; Wang, Zhenhai; Zhang, Jin; Esfahani, M Mahdi Davari; Zhou, Xiang-Feng; Wu, Fugen; Zhu, Qiang
2016-08-08
Boron suboxide B6O, the hardest known oxide, has an Rm crystal structure (α-B6O) that can be described as an oxygen-stuffed structure of α-boron, or, equivalently, as a cubic close packing of B12 icosahedra with two oxygen atoms occupying all octahedral voids in it. Here we show a new ground state of this compound at ambient conditions, Cmcm-B6O (β-B6O), which in all quantum-mechanical treatments that we tested comes out to be slightly but consistently more stable. Increasing pressure and temperature further stabilizes it with respect to the known α-B6O structure. β-B6O also has a slightly higher hardness and may be synthesized using different experimental protocols. We suggest that β-B6O is present in mixture with α-B6O, and its presence accounts for previously unexplained bands in the experimental Raman spectrum.
Prediction of a new ground state of superhard compound B6O at ambient conditions
NASA Astrophysics Data System (ADS)
Dong, Huafeng; Oganov, Artem R.; Wang, Qinggao; Wang, Sheng-Nan; Wang, Zhenhai; Zhang, Jin; Esfahani, M. Mahdi Davari; Zhou, Xiang-Feng; Wu, Fugen; Zhu, Qiang
2016-08-01
Boron suboxide B6O, the hardest known oxide, has an Rm crystal structure (α-B6O) that can be described as an oxygen-stuffed structure of α-boron, or, equivalently, as a cubic close packing of B12 icosahedra with two oxygen atoms occupying all octahedral voids in it. Here we show a new ground state of this compound at ambient conditions, Cmcm-B6O (β-B6O), which in all quantum-mechanical treatments that we tested comes out to be slightly but consistently more stable. Increasing pressure and temperature further stabilizes it with respect to the known α-B6O structure. β-B6O also has a slightly higher hardness and may be synthesized using different experimental protocols. We suggest that β-B6O is present in mixture with α-B6O, and its presence accounts for previously unexplained bands in the experimental Raman spectrum.
Prediction of a new ground state of superhard compound B6O at ambient conditions
Dong, Huafeng; Oganov, Artem R.; Wang, Qinggao; Wang, Sheng-Nan; Wang, Zhenhai; Zhang, Jin; Esfahani, M. Mahdi Davari; Zhou, Xiang-Feng; Wu, Fugen; Zhu, Qiang
2016-01-01
Boron suboxide B6O, the hardest known oxide, has an Rm crystal structure (α-B6O) that can be described as an oxygen-stuffed structure of α-boron, or, equivalently, as a cubic close packing of B12 icosahedra with two oxygen atoms occupying all octahedral voids in it. Here we show a new ground state of this compound at ambient conditions, Cmcm-B6O (β-B6O), which in all quantum-mechanical treatments that we tested comes out to be slightly but consistently more stable. Increasing pressure and temperature further stabilizes it with respect to the known α-B6O structure. β-B6O also has a slightly higher hardness and may be synthesized using different experimental protocols. We suggest that β-B6O is present in mixture with α-B6O, and its presence accounts for previously unexplained bands in the experimental Raman spectrum. PMID:27498718
Prediction of a new ground state of superhard compound B6O at ambient conditions.
Dong, Huafeng; Oganov, Artem R; Wang, Qinggao; Wang, Sheng-Nan; Wang, Zhenhai; Zhang, Jin; Esfahani, M Mahdi Davari; Zhou, Xiang-Feng; Wu, Fugen; Zhu, Qiang
2016-01-01
Boron suboxide B6O, the hardest known oxide, has an Rm crystal structure (α-B6O) that can be described as an oxygen-stuffed structure of α-boron, or, equivalently, as a cubic close packing of B12 icosahedra with two oxygen atoms occupying all octahedral voids in it. Here we show a new ground state of this compound at ambient conditions, Cmcm-B6O (β-B6O), which in all quantum-mechanical treatments that we tested comes out to be slightly but consistently more stable. Increasing pressure and temperature further stabilizes it with respect to the known α-B6O structure. β-B6O also has a slightly higher hardness and may be synthesized using different experimental protocols. We suggest that β-B6O is present in mixture with α-B6O, and its presence accounts for previously unexplained bands in the experimental Raman spectrum. PMID:27498718
Morgada, Marcos N; Abriata, Luciano A; Zitare, Ulises; Alvarez-Paggi, Damian; Murgida, Daniel H; Vila, Alejandro J
2014-06-10
The Cu(A) center is a dinuclear copper site that serves as an optimized hub for long-range electron transfer in heme-copper terminal oxidases. Its electronic structure can be described in terms of a σ(u)* ground-state wavefunction with an alternative, less populated ground state of π(u) symmetry, which is thermally accessible. It is now shown that second-sphere mutations in the Cu(A) containing subunit of Thermus thermophilus ba3 oxidase perturb the electronic structure, which leads to a substantial increase in the population of the π(u) state, as shown by different spectroscopic methods. This perturbation does not affect the redox potential of the metal site, and despite an increase in the reorganization energy, it is not detrimental to the electron-transfer kinetics. The mutations were achieved by replacing the loops that are involved in protein-protein interactions with cytochrome c, suggesting that transient protein binding could also elicit ground-state switching in the oxidase, which enables alternative electron-transfer pathways.
Davis, I.L.
1983-01-01
Two methods for calculating state-changing collisional matrix elements, and hence angular-momentum-mixing cross sections, are presented for a ground state noble gas atom colliding with a Rydberg atom at thermal energies. The first is a fully quantal method using Monte Carlo integration to perform the necessary nonseparable fifteen-dimensional collision integrals. The equations are developed for general treatment in the first and higher Born approximations, the distorted wave approximations,and several close-coupling schemes. The Monte Carlo method is carefully developed and tested for use in the types of integrals involved, and variance reduction techniques are discussed and applied. The second method uses a Gegenbauer polynomial expansion of the -1/r/sup 4/ polarization potential to find the necessary matrix elements. It also employs the elliptic functions and elliptic integrals to calculate the classical trajectory of the ground state atom as it passes the ionic Rydberg core. This semiclassical method is easily transformed into a fully quantal method, retaining only the polarization potential feature, by integrating the translational wave function of the incoming ground state atom and the matrix elements calculated via the Gegenbauer polynomials. The equations of scattering for the first quantal method are then specifically developed for ground state helium colliding with Rydberg helium, and calculation of the l-mixing cross section for He(10/sup 1/P) is performed using over a half million random fifteen-dimensional points. The result, accurate to within a factor of two, gives a result of 1600 A/sup 2/ compared to the experimental value of 2580 +/- 590 A/sup 2/. This experimental value is within the variance of the Monte Carlo calculation.
Effective Ginzburg-Landau free energy functional for multi-band isotropic superconductors
NASA Astrophysics Data System (ADS)
Grigorishin, Konstantin V.
2016-04-01
It has been shown that interband mixing of gradients of two order parameters (drag effect) in an isotropic bulk two-band superconductor plays important role - such a quantity of the intergradients coupling exists that the two-band superconductor is characterized with a single coherence length and a single Ginzburg-Landau (GL) parameter. Other quantities or neglecting of the drag effect lead to existence of two coherence lengths and dynamical instability due to violation of the phase relations between the order parameters. Thus so-called type-1.5 superconductors are impossible. An approximate method for solving of set of GL equations for a multi-band superconductor has been developed: using the result about the drag effect it has been shown that the free-energy functional for a multi-band superconductor can be reduced to the GL functional for an effective single-band superconductor.
Strain-Induced Energy Band Gap Opening in Two-Dimensional Bilayered Silicon Film
NASA Astrophysics Data System (ADS)
Ji, Z.; Zhou, R.; Lew Yan Voon, L. C.; Zhuang, Y.
2016-10-01
This work presents a theoretical study of the structural and electronic properties of bilayered silicon film (BiSF) under in-plane biaxial strain/stress using density functional theory (DFT). Atomic structures of the two-dimensional (2-D) silicon films are optimized by using both the local-density approximation (LDA) and generalized gradient approximation (GGA). In the absence of strain/stress, five buckled hexagonal honeycomb structures of the BiSF with triangular lattice have been obtained as local energy minima, and their structural stability has been verified. These structures present a Dirac-cone shaped energy band diagram with zero energy band gaps. Applying a tensile biaxial strain leads to a reduction of the buckling height. Atomically flat structures with zero buckling height have been observed when the AA-stacking structures are under a critical biaxial strain. Increase of the strain between 10.7% and 15.4% results in a band-gap opening with a maximum energy band gap opening of ˜0.17 eV, obtained when a 14.3% strain is applied. Energy band diagrams, electron transmission efficiency, and the charge transport property are calculated. Additionally, an asymmetric energetically favorable atomic structure of BiSF shows a non-zero band gap in the absence of strain/stress and a maximum band gap of 0.15 eV as a -1.71% compressive strain is applied. Both tensile and compressive strain/stress can lead to a band gap opening in the asymmetric structure.
Energy Band and Josephson Dynamics of Spin-Orbit Coupled Bose-Einstein Condensates
NASA Astrophysics Data System (ADS)
Zhang, Xin; Yu, Zi-Fa; Xue, Ju-Kui
2015-10-01
We theoretically investigate the energy band structure and Josephson dynamics of a spin-orbit coupled Bose-Einstein condensate in a double-well potential. We study the energy band structure and the corresponding tunneling dynamics of the system by properly adjusting the SO coupling, Raman coupling, Zeeman field and atomic interactions. The coupled effects of SO coupling, Raman coupling, Zeeman field and atomic interactions lead to the appearance of complex energy band structure including the loop structure. Particularly, the emergence of the loop structure in energy band also depends on SO coupling, Raman coupling, Zeeman field and atomic interactions. Correspondingly, the Josephson dynamics of the system are strongly related to the energy band structure. Especially, the emergence of the loop structure results in complex tunneling dynamics, including suppression-revival transitions and self-trapping of atoms transfer between two spin states and two wells. This engineering provides a possible means for studying energy level and corresponding dynamics of two-species SO coupled BECs. Supported by the National Natural Science Foundation of China under Grant Nos. 11274255 and 11305132, by Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No. 20136203110001, by the Natural Science Foundation of Gansu province under Grant No. 2011GS04358, and by Creation of Science and Technology of Northwest Normal University under Grant Nos. NWNU-KJCXGC-03-48, NWNU-LKQN-12-12
Rotational bands in 11B and identification of diluted states
NASA Astrophysics Data System (ADS)
Demyanova, A. S.; Danilov, A. N.; Ogloblin, A. A.; Goncharov, S. A.; Belyaeva, T. L.; Trzaska, W.
2016-06-01
Differential cross-sections of the 11B + α inelastic scattering at E(α) = 65 leading to the most of the known 11B states at the excitation energies up to 14 MeV were measured. The data analysis was done by DWBA and in some cases by the modified diffraction model allowing determining the radii of the excited states. The radii of the states with excitation energies less than ∼ 7 MeV with the accuracy not less than 0.1-0.15 fm coincide with the radius of the ground state. This result is consistent with the traditional view of the shell structure of the low-lying states in 11B. Most of the observed high-energy excited states are distributed among four rotational bands. The moments of inertia of band states are close to the moment of inertia of the Hoyle state of 12C. The calculated radii, related to these bands, are 0.7 - 1.0 fm larger than the radius of the ground state, and are close to the radius of the Hoyle state. These results are in agreement with existing predictions about various cluster structure of 11B at high excitation energies. The state with the excitation energy 12.56 MeV, I π = 1/2+, T = 1/2 and the root mean square radius R ∼ 6 fm predicted in the frame of the alpha condensate hypothesis was not found.
Hrovat, David; Hou, Gao-Lei; Chen, Bo; Wang, Xue B.; Borden, Weston
2015-11-13
The CO_{3} radical anion (CO_{3}^{•–}) has been formed by electrospraying carbonate dianion (CO_{3}^{2–}) into the gas phase. The negative ion photoelectron (NIPE) spectrum of CO_{3}^{•– }shows that, unlike trimethylenemethane [C(CH_{2})_{3}], carbontrioxide (CO_{3}) has a singlet ground state. From the NIPE spectrum, the electron affinity of CO_{3} was determined to be EA = 4.06 ± 0.03 eV, and the singlet-triplet energy difference was found to be ΔEST = - 17.8 ± 0.9 kcal/mol. B3LYP, CCSD(T), and CASPT2 calculations all find that the two lowest triplet states of CO_{3} are very close in energy, a prediction that is confirmed by the relative intensities of the bands in the NIPE spectrum of CO_{3}^{•–}. The 560 cm^{-1} vibrational progression, seen in the low energy region of the triplet band, enables the identification of the lowest, Jahn-Teller-distorted, triplet state as ^{3}A_{1}, in which both unpaired electrons reside in σ MOs, rather than ^{3}A_{2}, in which one unpaired electron occupies the b_{2} σ MO, and the other occupies the b_{1} π MO.
Ground-state phase diagram of the one-dimensional half-filled extended Hubbard model
NASA Astrophysics Data System (ADS)
Tsuchiizu, M.; Furusaki, A.
2004-01-01
We revisit the ground-state phase diagram of the one-dimensional half-filled extended Hubbard model with on-site (U) and nearest-neighbor (V) repulsive interactions. In the first half of the paper, using the weak-coupling renormalization-group approach (g-ology) including second-order corrections to the coupling constants, we show that bond-charge-density-wave (BCDW) phase exists for U≈2V in between charge-density-wave (CDW) and spin-density-wave (SDW) phases. We find that the umklapp scattering of parallel-spin electrons disfavors the BCDW state and leads to a bicritical point where the CDW-BCDW and SDW-BCDW continuous-transition lines merge into the CDW-SDW first-order transition line. In the second half of the paper, we investigate the phase diagram of the extended Hubbard model with either additional staggered site potential Δ or bond alternation δ. Although the alternating site potential Δ strongly favors the CDW state (that is, a band insulator), the BCDW state is not destroyed completely and occupies a finite region in the phase diagram. Our result is a natural generalization of the work by Fabrizio, Gogolin, and Nersesyan [Phys. Rev. Lett. 83, 2014 (1999)], who predicted the existence of a spontaneously dimerized insulating state between a band insulator and a Mott insulator in the phase diagram of the ionic Hubbard model. The bond alternation δ destroys the SDW state and changes it into the BCDW state (or Peierls insulating state). As a result the phase diagram of the model with δ contains only a single critical line separating the Peierls insulator phase and the CDW phase. The addition of Δ or δ changes the universality class of the CDW-BCDW transition from the Gaussian transition into the Ising transition.
Local-spin-density calculations for iron: Effect of spin interpolation on ground-state properties
NASA Astrophysics Data System (ADS)
MacLaren, J. M.; Clougherty, D. P.; Albers, R. C.
1990-08-01
Scalar-relativistic self-consistent linear muffin-tin orbital (LMTO) calculations for bcc and fcc Fe have been performed with several different local approximations to the exchange and correlation energy density and potential. Overall, in contrast to the conclusions of previous studies, we find that the local-spin-density approximation to exchange and correlation can provide an adequate description of bulk Fe provided that a proper parametrization of the correlation energy density and potential of the homogeneous electron gas over both spin and density is used. Lattice constants, found from the position of the minimum of the total energy as a function of Wigner-Seitz radius, agree to within 1% (for s,p,d LMTO's only) and within 1-2% (for s,p,d,f LMTO's) of the experimental lattice constants for all forms used for the local correlation. The best agreement, however, was obtained using a local correlation potential derived from the Vosko-Wilk-Nusair form for the spin dependence of the correlation energy density. The calculation performed with this correlation potential was also the only calculation to correctly predict a bcc ferromagnetic ground state.
Observation of the bottomonium ground state in the decay Upsilon(3S)-->gammaetab.
Aubert, B; Bona, M; Karyotakis, Y; Lees, J P; Poireau, V; Prencipe, E; Prudent, X; Tisserand, V; Garra Tico, J; Grauges, E; Lopez, L; Palano, A; Pappagallo, M; Eigen, G; Stugu, B; Sun, L; Abrams, G S; Battaglia, M; Brown, D N; Cahn, R N; Jacobsen, R G; Kerth, L T; Kolomensky, Yu G; Lynch, G; Osipenkov, I L; Ronan, M T; Tackmann, K; Tanabe, T; Hawkes, C M; Soni, N; Watson, A T; Koch, H; Schroeder, T; Walker, D; Asgeirsson, D J; Fulsom, B G; Hearty, C; Mattison, T S; McKenna, J A; Barrett, M; Khan, A; Blinov, V E; Bukin, A D; Buzykaev, A R; Druzhinin, V P; Golubev, V B; Onuchin, A P; Serednyakov, S I; Skovpen, Yu I; Solodov, E P; Todyshev, K Yu; Bondioli, M; Curry, S; Eschrich, I; Kirkby, D; Lankford, A J; Lund, P; Mandelkern, M; Martin, E C; Stoker, D P; Abachi, S; Buchanan, C; Gary, J W; Liu, F; Long, O; Shen, B C; Vitug, G M; Yasin, Z; Zhang, L; Sharma, V; Campagnari, C; Hong, T M; Kovalskyi, D; Mazur, M A; Richman, J D; Beck, T W; Eisner, A M; Flacco, C J; Heusch, C A; Kroseberg, J; Lockman, W S; Martinez, A J; Schalk, T; Schumm, B A; Seiden, A; Wilson, M G; Winstrom, L O; Cheng, C H; Doll, D A; Echenard, B; Fang, F; Hitlin, D G; Narsky, I; Piatenko, T; Porter, F C; Andreassen, R; Mancinelli, G; Meadows, B T; Mishra, K; Sokoloff, M D; Bloom, P C; Ford, W T; Gaz, A; Hirschauer, J F; Nagel, M; Nauenberg, U; Smith, J G; Ulmer, K A; Wagner, S R; Ayad, R; Soffer, A; Toki, W H; Wilson, R J; Altenburg, D D; Feltresi, E; Hauke, A; Jasper, H; Karbach, M; Merkel, J; Petzold, A; Spaan, B; Wacker, K; Kobel, M J; Mader, W F; Nogowski, R; Schubert, K R; Schwierz, R; Volk, A; Bernard, D; Bonneaud, G R; Latour, E; Verderi, M; Clark, P J; Playfer, S; Watson, J E; Andreotti, M; Bettoni, D; Bozzi, C; Calabrese, R; Cecchi, A; Cibinetto, G; Franchini, P; Luppi, E; Negrini, M; Petrella, A; Piemontese, L; Santoro, V; Baldini-Ferroli, R; Calcaterra, A; de Sangro, R; Finocchiaro, G; Pacetti, S; Patteri, P; Peruzzi, I M; Piccolo, M; Rama, M; Zallo, A; Buzzo, A; Contri, R; Lo Vetere, M; Macri, M M; Monge, M R; Passaggio, S; Patrignani, C; Robutti, E; Santroni, A; Tosi, S; Chaisanguanthum, K S; Morii, M; Adametz, A; Marks, J; Schenk, S; Uwer, U; Klose, V; Lacker, H M; Bard, D J; Dauncey, P D; Nash, J A; Tibbetts, M; Behera, P K; Chai, X; Charles, M J; Mallik, U; Cochran, J; Crawley, H B; Dong, L; Meyer, W T; Prell, S; Rosenberg, E I; Rubin, A E; Gao, Y Y; Gritsan, A V; Guo, Z J; Lae, C K; Arnaud, N; Béquilleux, J; D'Orazio, A; Davier, M; da Costa, J Firmino; Grosdidier, G; Höcker, A; Lepeltier, V; Le Diberder, F; Lutz, A M; Pruvot, S; Roudeau, P; Schune, M H; Serrano, J; Sordini, V; Stocchi, A; Wormser, G; Lange, D J; Wright, D M; Bingham, I; Burke, J P; Chavez, C A; Fry, J R; Gabathuler, E; Gamet, R; Hutchcroft, D E; Payne, D J; Touramanis, C; Bevan, A J; Clarke, C K; George, K A; Di Lodovico, F; Sacco, R; Sigamani, M; Cowan, G; Flaecher, H U; Hopkins, D A; Paramesvaran, S; Salvatore, F; Wren, A C; Brown, D N; Davis, C L; Denig, A G; Fritsch, M; Gradl, W; Schott, G; Alwyn, K E; Bailey, D; Barlow, R J; Chia, Y M; Edgar, C L; Jackson, G; Lafferty, G D; West, T J; Yi, J I; Anderson, J; Chen, C; Jawahery, A; Roberts, D A; Simi, G; Tuggle, J M; Dallapiccola, C; Li, X; Salvati, E; Saremi, S; Cowan, R; Dujmic, D; Fisher, P H; Sciolla, G; Spitznagel, M; Taylor, F; Yamamoto, R K; Zhao, M; Patel, P M; Robertson, S H; Lazzaro, A; Lombardo, V; Palombo, F; Bauer, J M; Cremaldi, L; Godang, R; Kroeger, R; Sanders, D A; Summers, D J; Zhao, H W; Simard, M; Taras, P; Viaud, F B; Nicholson, H; De Nardo, G; Lista, L; Monorchio, D; Onorato, G; Sciacca, C; Raven, G; Snoek, H L; Jessop, C P; Knoepfel, K J; LoSecco, J M; Wang, W F; Benelli, G; Corwin, L A; Honscheid, K; Kagan, H; Kass, R; Morris, J P; Rahimi, A M; Regensburger, J J; Sekula, S J; Wong, Q K; Blount, N L; Brau, J; Frey, R; Igonkina, O; Kolb, J A; Lu, M; Rahmat, R; Sinev, N B; Strom, D; Strube, J; Torrence, E; Castelli, G; Gagliardi, N; Margoni, M; Morandin, M; Posocco, M; Rotondo, M; Simonetto, F; Stroili, R; Voci, C; del Amo Sanchez, P; Ben-Haim, E; Briand, H; Calderini, G; Chauveau, J; David, P; Del Buono, L; Hamon, O; Leruste, Ph; Ocariz, J; Perez, A; Prendki, J; Sitt, S; Gladney, L; Biasini, M; Covarelli, R; Manoni, E; Angelini, C; Batignani, G; Bettarini, S; Carpinelli, M; Cervelli, A; Forti, F; Giorgi, M A; Lusiani, A; Marchiori, G; Morganti, M; Neri, N; Paoloni, E; Rizzo, G; Walsh, J J; Lopes Pegna, D; Lu, C; Olsen, J; Smith, A J S; Telnov, A V; Anulli, F; Baracchini, E; Cavoto, G; del Re, D; Di Marco, E; Faccini, R; Ferrarotto, F; Ferroni, F; Gaspero, M; Jackson, P D; Gioi, L Li; Mazzoni, M A; Morganti, S; Piredda, G; Polci, F; Renga, F; Voena, C; Ebert, M; Hartmann, T; Schröder, H; Waldi, R; Adye, T; Franek, B; Olaiya, E O; Wilson, F F; Emery, S; Escalier, M; Esteve, L; Ganzhur, S F; de Monchenault, G Hamel; Kozanecki, W; Vasseur, G; Yèche, Ch; Zito, M; Chen, X R; Liu, H; Park, W; Purohit, M V; White, R M; Wilson, J R; Allen, M T; Aston, D; Bartoldus, R; Bechtle, P; Benitez, J F; Bertsche, K; Cai, Y; Cenci, R; Coleman, J P; Convery, M R; Decker, F J; Dingfelder, J C; Dorfan, J; Dubois-Felsmann, G P; Dunwoodie, W; Ecklund, S; Erickson, R; Field, R C; Fisher, A; Fox, J; Gabareen, A M; Gowdy, S J; Graham, M T; Grenier, P; Hast, C; Innes, W R; Iverson, R; Kaminski, J; Kelsey, M H; Kim, H; Kim, P; Kocian, M L; Kulikov, A; Leith, D W G S; Li, S; Lindquist, B; Luitz, S; Luth, V; Lynch, H L; Macfarlane, D B; Marsiske, H; Messner, R; Muller, D R; Neal, H; Nelson, S; Novokhatski, A; O'Grady, C P; Ofte, I; Perazzo, A; Perl, M; Ratcliff, B N; Rivetta, C; Roodman, A; Salnikov, A A; Schindler, R H; Schwiening, J; Seeman, J; Snyder, A; Su, D; Sullivan, M K; Suzuki, K; Swain, S K; Thompson, J M; Va'vra, J; Van Winkle, D; Wagner, A P; Weaver, M; West, C A; Wienands, U; Wisniewski, W J; Wittgen, M; Wittmer, W; Wright, D H; Wulsin, H W; Yan, Y; Yarritu, A K; Yi, K; Yocky, G; Young, C C; Ziegler, V; Burchat, P R; Edwards, A J; Majewski, S A; Miyashita, T S; Petersen, B A; Wilden, L; Ahmed, S; Alam, M S; Ernst, J A; Pan, B; Saeed, M A; Zain, S B; Spanier, S M; Wogsland, B J; Eckmann, R; Ritchie, J L; Ruland, A M; Schilling, C J; Schwitters, R F; Drummond, B W; Izen, J M; Lou, X C; Bianchi, F; Gamba, D; Pelliccioni, M; Bomben, M; Bosisio, L; Cartaro, C; Della Ricca, G; Lanceri, L; Vitale, L; Azzolini, V; Lopez-March, N; Martinez-Vidal, F; Milanes, D A; Oyanguren, A; Albert, J; Banerjee, Sw; Bhuyan, B; Choi, H H F; Hamano, K; Kowalewski, R; Lewczuk, M J; Nugent, I M; Roney, J M; Sobie, R J; Gershon, T J; Harrison, P F; Ilic, J; Latham, T E; Mohanty, G B; Band, H R; Chen, X; Dasu, S; Flood, K T; Pan, Y; Pierini, M; Prepost, R; Vuosalo, C O; Wu, S L
2008-08-15
We report the results of a search for the bottomonium ground state etab(1S) in the photon energy spectrum with a sample of (109+/-1) million of Upsilon(3S) recorded at the Upsilon(3S) energy with the BABAR detector at the PEP-II B factory at SLAC. We observe a peak in the photon energy spectrum at Egamma=921.2(-2.8)+2.1(stat)+/-2.4(syst) MeV with a significance of 10 standard deviations. We interpret the observed peak as being due to monochromatic photons from the radiative transition Upsilon(3S)-->gammaetab(1S). This photon energy corresponds to an etab(1S) mass of 9388.9(-2.3)+3.1(stat)+/-2.7(syst) MeV/c2. The hyperfine Upsilon(1S)-etab(1S) mass splitting is 71.4(-3.1)+2.3(stat)+/-2.7(syst) MeV/c2. The branching fraction for this radiative Upsilon(3S) decay is estimated to be [4.8+/-0.5(stat)+/-1.2(syst)]x10(-4). PMID:18764521
Wedge energy bands of monolayer black phosphorus: a first-principles study
NASA Astrophysics Data System (ADS)
Park, Minwoo; Bae, Hyeonhu; Lee, Seunghan; Yang, Li; Lee, Hoonkyung
2016-08-01
On the basis of first-principles calculations, we present intriguing electronic properties of halogen-striped functionalized monolayer black phosphorus. The halogen-striped monolayer black phosphorus is found to have a wedge energy band with the energy-momentum relation of E\\propto {{p}y} when the stripe–stripe distance is smaller than ~40 Å. Our tight-binding study shows that the wedge energy band occurs when 2-atom basis 1D lattices are periodically repeated aligned with each other in a 2D lattice. We also discuss the possible applications of this wedge energy band in electron supercollimation with high mobility or severely anisotropic electronic transport, which can be used for the development of optics-like nano-electronics.
Wedge energy bands of monolayer black phosphorus: a first-principles study
NASA Astrophysics Data System (ADS)
Park, Minwoo; Bae, Hyeonhu; Lee, Seunghan; Yang, Li; Lee, Hoonkyung
2016-08-01
On the basis of first-principles calculations, we present intriguing electronic properties of halogen-striped functionalized monolayer black phosphorus. The halogen-striped monolayer black phosphorus is found to have a wedge energy band with the energy-momentum relation of E\\propto {{p}y} when the stripe-stripe distance is smaller than ~40 Å. Our tight-binding study shows that the wedge energy band occurs when 2-atom basis 1D lattices are periodically repeated aligned with each other in a 2D lattice. We also discuss the possible applications of this wedge energy band in electron supercollimation with high mobility or severely anisotropic electronic transport, which can be used for the development of optics-like nano-electronics.
Wedge energy bands of monolayer black phosphorus: a first-principles study.
Park, Minwoo; Bae, Hyeonhu; Lee, Seunghan; Yang, Li; Lee, Hoonkyung
2016-08-01
On the basis of first-principles calculations, we present intriguing electronic properties of halogen-striped functionalized monolayer black phosphorus. The halogen-striped monolayer black phosphorus is found to have a wedge energy band with the energy-momentum relation of [Formula: see text] when the stripe-stripe distance is smaller than ~40 Å. Our tight-binding study shows that the wedge energy band occurs when 2-atom basis 1D lattices are periodically repeated aligned with each other in a 2D lattice. We also discuss the possible applications of this wedge energy band in electron supercollimation with high mobility or severely anisotropic electronic transport, which can be used for the development of optics-like nano-electronics. PMID:27299467
Rane, Vinayak; Kundu, Sushma; Das, Ranjan
2015-09-01
A series of molecules containing a naphthalene chromophore and a stable free radical 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) covalently linked by a spacer group of different lengths have been synthesized. In n-hexane solution, their photophysical behavior was studied and compared with a system of freely moving naphthalene and the free radical TEMPO. The linked molecules showed strong quenching of the singlet and triplet states of the naphthalene moiety, compared to when naphthalene and TEMPO were not linked. The quenching efficiency decreased with increasing the length of the spacer group. In addition, new electronic absorption and emission bands, along with the usual bands of the individual moieties, were also seen. These news bands have been attributed to the formation of electron donor-acceptor charge-transfer complexes in the ground state, arising from the interaction between the two moieties in close proximity. The photophysical dynamics of the linked molecules has been rationalized by assuming the existence of two types of population of the linked molecules: folded and extended. The ground state complex formation is proposed to occur only in the folded conformation of the linked molecules. To our knowledge, this is possibly the first example of a ground state charge-transfer complex formation involving a TEMPO free radical and naphthalene.
Exact ground states of large two-dimensional planar Ising spin glasses
NASA Astrophysics Data System (ADS)
Pardella, G.; Liers, F.
2008-11-01
Studying spin-glass physics through analyzing their ground-state properties has a long history. Although there exist polynomial-time algorithms for the two-dimensional planar case, where the problem of finding ground states is transformed to a minimum-weight perfect matching problem, the reachable system sizes have been limited both by the needed CPU time and by memory requirements. In this work, we present an algorithm for the calculation of exact ground states for two-dimensional Ising spin glasses with free boundary conditions in at least one direction. The algorithmic foundations of the method date back to the work of Kasteleyn from the 1960s for computing the complete partition function of the Ising model. Using Kasteleyn cities, we calculate exact ground states for huge two-dimensional planar Ising spin-glass lattices (up to 30002 spins) within reasonable time. According to our knowledge, these are the largest sizes currently available. Kasteleyn cities were recently also used by Thomas and Middleton in the context of extended ground states on the torus. Moreover, they show that the method can also be used for computing ground states of planar graphs. Furthermore, we point out that the correctness of heuristically computed ground states can easily be verified. Finally, we evaluate the solution quality of heuristic variants of the L. Bieche approach.
Bes, D. R.; Civitarese, O.
2010-01-15
Theoretical matrix elements, for the ground-state to ground-state two-neutrino double-{beta}-decay mode (2{nu}{beta}{sup -}{beta}{sup -}gs->gs) of {sup 128,130}Te isotopes, are calculated within a formalism that describes interactions between neutrons in a superfluid phase and protons in a normal phase. The elementary degrees of freedom of the model are proton-pair modes and pairs of protons and quasineutrons. The calculation is basically a parameter-free one, because all relevant parameters are fixed from the phenomenology. A comparison with the available experimental data is presented.
NASA Astrophysics Data System (ADS)
Klubnuan, Sarunya; Suwanboon, Sumetha; Amornpitoksuk, Pongsaton
2016-03-01
The dependence of the crystallite size and the band tail energy on the optical properties, particle shape and oxygen vacancy of different ZnO nanostructures to catalyse photocatalytic degradation was investigated. The ZnO nanoplatelets and mesh-like ZnO lamellae were synthesized from the PEO19-b-PPO3 modified zinc acetate dihydrate using aqueous KOH and CO(NH2)2 solutions, respectively via a hydrothermal method. The band tail energy of the ZnO nanostructures had more influence on the band gap energy than the crystallite size. The photocatalytic degradation of methylene blue increased as a function of the irradiation time, the amount of oxygen vacancy and the intensity of the (0 0 0 2) plane. The ZnO nanoplatelets exhibited a better photocatalytic degradation of methylene blue than the mesh-like ZnO lamellae due to the migration of the photoelectrons and holes to the (0 0 0 1) and (0 0 0 -1) planes, respectively under the internal electric field, that resulted in the enhancement of the photocatalytic activities.
NASA Technical Reports Server (NTRS)
Danilowicz, R.
1973-01-01
Ground-state properties of quantum crystals have received considerable attention from both theorists and experimentalists. The theoretical results have varied widely with the Monte Carlo calculations being the most successful. The molecular field approximation yields ground-state properties which agree closely with the Monte Carlo results. This approach evaluates the dynamical behavior of each pair of molecules in the molecular field of the other N-2 molecules. In addition to predicting ground-state properties that agree well with experiment, this approach yields data on the relative importance of interactions of different nearest neighbor pairs.
Ground state properties of superheavy nuclei with Z=117 and Z=119
Ren Zhongzhou; Chen Dinghan; Xu Chang
2006-11-02
We review the current studies on the ground-state properties of superheavy nuclei. It is shown that there is shape coexistence for the ground state of many superheavy nuclei from different models and many superheavy nuclei are deformed. This can lead to the existence of isomers in superheavy region and it plays an important role for the stability of superheavy nuclei. Some new results on Z=117 and Z=119 isotopes are presented. The agreement between theoretical results and experimental data clearly demonstrates the validity of theoretical models for the ground-state properties of superheavy nuclei.
Low-energy rotational bands in the nucleus155Eu
NASA Astrophysics Data System (ADS)
Katajanheimo, R.; Liljavirta, H.; Siivola, A.; Hammarén, E.; Liukkonen, E.
1984-02-01
Excited states in the nucleus155Eu have been produced during in-beam bombardments of a154Sm target with3He beams at 22 and 27 MeV. Decay gamma rays were detected using coincidence equipment optimized for low-energy photons. The level scheme is based on the observed γγ-coincidence relationships combined with the information on relative intensities. Tentatively suggested spin assignments follow from the apparent rotational character of the nucleus. Experimental observations are compared with predictions calculated from a particle-rotor model with a nonspheroidal Woods-Saxon potential.
Strongly correlated flat-band systems: The route from Heisenberg spins to Hubbard electrons
NASA Astrophysics Data System (ADS)
Derzhko, Oleg; Richter, Johannes; Maksymenko, Mykola
2015-05-01
On a large class of lattices (such as the sawtooth chain, the kagome and the pyrochlore lattices), the quantum Heisenberg and the repulsive Hubbard models may host a completely dispersionless (flat) energy band in the single-particle spectrum. The flat-band states can be viewed as completely localized within a finite volume (trap) of the lattice and allow for construction of many-particle states, roughly speaking, by occupying the traps with particles. If the flat-band happens to be the lowest-energy one, the manifold of such many-body states will often determine the ground-state and low-temperature physics of the models at hand even in the presence of strong interactions. The localized nature of these many-body states makes possible the mapping of this subset of eigenstates onto a corresponding classical hard-core system. As a result, the ground-state and low-temperature properties of the strongly correlated flat-band systems can be analyzed in detail using concepts and tools of classical statistical mechanics (e.g., classical lattice-gas approach or percolation approach), in contrast to more challenging quantum many-body techniques usually necessary to examine strongly correlated quantum systems. In this review, we recapitulate the basic features of the flat-band spin systems and briefly summarize earlier studies in the field. The main emphasis is made on recent developments which include results for both spin and electron flat-band models. In particular, for flat-band spin systems, we highlight field-driven phase transitions for frustrated quantum Heisenberg antiferromagnets at low temperatures, chiral flat-band states, as well as the effect of a slight dispersion of a previously strictly flat-band due to nonideal lattice geometry. For electronic systems, we discuss the universal low-temperature behavior of several flat-band Hubbard models, the emergence of ground-state ferromagnetism in the square-lattice Tasaki-Hubbard model and the related Pauli
Characterization of the HSiN HNSi system in its electronic ground state
NASA Astrophysics Data System (ADS)
Lind, Maria C.; Pickard, Frank C.; Ingels, Justin B.; Paul, Ankan; Yamaguchi, Yukio; Schaefer, Henry F.
2009-03-01
The electronic ground states (X˜Σ+1) of HSiN, HNSi, and the transition state connecting the two isomers were systematically studied using configuration interaction with single and double (CISD) excitations, coupled cluster with single and double (CCSD) excitations, CCSD with perturbative triple corrections [CCSD(T)], multireference complete active space self-consistent field (CASSCF), and internally contracted multireference configuration interaction (ICMRCI) methods. The correlation-consistent polarized valence (cc-pVXZ), augmented correlation-consistent polarized valence (aug-cc-pVXZ) (X=T,Q,5), correlation-consistent polarized core-valence (cc-pCVYZ), and augmented correlation-consistent polarized core-valence (aug-cc-pCVYZ) (Y=T,Q) basis sets were used. Via focal point analyses, we confirmed the HNSi isomer as the global minimum on the ground state HSiN HNSi zero-point vibrational energy corrected surface and is predicted to lie 64.7kcalmol-1 (22640cm-1, 2.81eV) below the HSiN isomer. The barrier height for the forward isomerization reaction (HSiN→HNSi) is predicted to be 9.7kcalmol-1, while the barrier height for the reverse process (HNSi→HSiN) is determined to be 74.4kcalmol-1. The dipole moments of the HSiN and HNSi isomers are predicted to be 4.36 and 0.26D, respectively. The theoretical vibrational isotopic shifts for the HSiN/DSiN and HNSi/DNSi isotopomers are in strong agreement with the available experimental values. The dissociation energy for HSiN [HSiN(X˜Σ+1)→H(S2)+SiN(XΣ+2)] is predicted to be D0=59.6kcalmol-1, whereas the dissociation energy for HNSi [HNSi(X˜Σ+1)→H(S2)+NSi(XΣ+2)] is predicted to be D0=125.0kcalmol-1 at the CCSD(T)/aug-cc-pCVQZ level of theory. Anharmonic vibrational frequencies computed using second order vibrational perturbation theory are in good agreement with available matrix isolation experimental data for both HSiN and HNSi isomers root mean squared derivation (RMSD=9cm-1).
Bisogni, Valentina; Catalano, Sara; Green, Robert J.; Gibert, Marta; Scherwitzl, Raoul; Huang, Yaobo; Strocov, Vladimir N.; Zubko, Pavlo; Balandeh, Shadi; Triscone, Jean-Marc; Sawatzky, George; Schmitt, Thorsten
2016-01-01
The metal–insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3 thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal–insulator transition in terms of bond disproportionation. PMID:27725665
NASA Astrophysics Data System (ADS)
Bisogni, Valentina; Catalano, Sara; Green, Robert J.; Gibert, Marta; Scherwitzl, Raoul; Huang, Yaobo; Strocov, Vladimir N.; Zubko, Pavlo; Balandeh, Shadi; Triscone, Jean-Marc; Sawatzky, George; Schmitt, Thorsten
2016-10-01
The metal-insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3 thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal-insulator transition in terms of bond disproportionation.
Energy dependence of the band-limited noise in black hole X-ray binaries★
NASA Astrophysics Data System (ADS)
Stiele, H.; Yu, W.
2015-10-01
Black hole low-mass X-ray binaries show a variety of variability features, which manifest as narrow peak-like structures superposed on broad noise components in power density spectra in the hard X-ray emission. In this work, we study variability properties of the band-limited noise component during the low-hard state for a sample of black hole X-ray binaries. We investigate the characteristic frequency and amplitude of the band-limited noise component and study covariance spectra. For observations that show a noise component with a characteristic frequency above 1 Hz in the hard energy band (4-8 keV), we found this very same component at a lower frequency in the soft band (1-2 keV). This difference in characteristic frequency is an indication that while both the soft and the hard band photons contribute to the same band-limited noise component, which likely represents the modulation of the mass accretion rate, the origin of the soft photons is actually further away from the black hole than the hard photons. Thus, the soft photons are characterized by larger radii, lower frequencies and softer energies, and are probably associated with a smaller optical depth for Comptonization up-scattering from the outer layer of the corona, or suggest a temperature gradient of the corona. We interpret this energy dependence within the picture of energy-dependent power density states as a hint that the contribution of the up-scattered photons originating in the outskirts of the Comptonizing corona to the overall emission in the soft band is becoming significant.
Effective parameters in beam acoustic metamaterials based on energy band structures
NASA Astrophysics Data System (ADS)
Jing, Li; Wu, Jiu Hui; Guan, Dong; Hou, Mingming; Kuan, Lu; Shen, Li
2016-07-01
We present a method to calculate the effective material parameters of beam acoustic metamaterials. The effective material parameters of a periodic beam are calculated as an example. The dispersion relations and energy band structures of this beam are calculated. Subsequently, the effective material parameters of the beam are investigated by using the energy band structures. Then, the modal analysis and transmission properties of the beams with finite cells are simulated in order to confirm the correctness of effective approximation. The results show that the periodic beam can be equivalent to the homogeneous beam with dynamic effective material parameters in passband.
Molecular spectroscopy for producing ultracold ground-state NaRb molecules
NASA Astrophysics Data System (ADS)
Wang, Dajun; Guo, Mingyang; Zhu, Bing; Lu, Bo; Ye, Xin; Wang, Fudong; Vexiau, Romain; Bouloufa-Maafa, Nadia; Quéméner, Goulven; Dulieu, Olivier
2016-05-01
Recently, we have successfully created an ultracold sample of absolute ground-state NaRb molecules by two-photon Raman transfer of weakly bound Feshbach molecules. Here we will present the detailed spectroscopic investigations on both the excited and the rovibrational ground states for finding the two-photon path. For the excited state, we focus on the A1Σ+ /b3 Π singlet and triplet admixture. We discovered an anomalously strong coupling between the Ω =0+ and 0- components which renders efficient population transfer possible. In the ground state, the pure nuclear hyperfine levels have been clearly resolved, which allows us to create molecules in the absolute ground state directly with Raman transfer. This work is jointly supported by Agence Nationale de la Recherche (#ANR-13- IS04-0004-01) and Hong Kong Research Grant Council (#A-CUHK403/13) through the COPOMOL project.
One-dimensional extended Hubbard model with spin-triplet pairing ground states
NASA Astrophysics Data System (ADS)
Tanaka, Akinori
2016-10-01
We show that the one-dimensional extended Hubbard model has saturated ferromagnetic ground states with the spin-triplet electron pair condensation in a certain range of parameters. The ground state wave functions with fixed electron numbers are explicitly obtained. We also construct two ground states in which both the spin-rotation and the gauge symmetries are broken, and show that these states are transferred from one to the other by applying the edge operators. The edge operators are reduced to the Majorana fermions in a special case. These symmetry breaking ground states are shown to be stabilized by a superconducting mean field Hamiltonian which is related to the Kitaev chain with the charge-charge interaction.
Bott Periodicity for Z_2 Symmetric Ground States of Gapped Free-Fermion Systems
NASA Astrophysics Data System (ADS)
Kennedy, R.; Zirnbauer, M. R.
2016-03-01
Building on the symmetry classification of disordered fermions, we give a proof of the proposal by Kitaev, and others, for a "Bott clock" topological classification of free-fermion ground states of gapped systems with symmetries. Our approach differs from previous ones in that (i) we work in the standard framework of Hermitian quantum mechanics over the complex numbers, (ii) we directly formulate a mathematical model for ground states rather than spectrally flattened Hamiltonians, and (iii) we use homotopy-theoretic tools rather than K-theory. Key to our proof is a natural transformation that squares to the standard Bott map and relates the ground state of a d-dimensional system in symmetry class s to the ground state of a ( d + 1)-dimensional system in symmetry class s + 1. This relation gives a new vantage point on topological insulators and superconductors.
No-go theorem for ground state cooling given initial system-thermal bath factorization
NASA Astrophysics Data System (ADS)
Wu, Lian-Ao; Segal, Dvira; Brumer, Paul
2013-05-01
Ground-state cooling and pure state preparation of a small object that is embedded in a thermal environment is an important challenge and a highly desirable quantum technology. This paper proves, with two different methods, that a fundamental constraint on the cooling dynamic implies that it is impossible to cool, via a unitary system-bath quantum evolution, a system that is embedded in a thermal environment down to its ground state, if the initial state is a factorized product of system and bath states. The latter is a crucial but artificial assumption included in numerous tools that treat system-bath dynamics, such as master equation approaches and Kraus operator based methods. Adopting these approaches to address ground state and even approximate ground state cooling dynamics should therefore be done with caution, considering the fundamental theorem exposed in this work.
Microscopic mechanism of 1/f noise in graphene: role of energy band dispersion.
Pal, Atindra Nath; Ghatak, Subhamoy; Kochat, Vidya; Sneha, E S; Sampathkumar, Arjun; Raghavan, Srinivasan; Ghosh, Arindam
2011-03-22
A distinctive feature of single-layer graphene is the linearly dispersive energy bands, which in the case of multilayer graphene become parabolic. A simple electrical transport-based probe to differentiate between these two band structures will be immensely valuable, particularly when quantum Hall measurements are difficult, such as in chemically synthesized graphene nanoribbons. Here we show that the flicker noise, or the 1/f noise, in electrical resistance is a sensitive and robust probe to the band structure of graphene. At low temperatures, the dependence of noise magnitude on the carrier density was found to be opposite for the linear and parabolic bands. We explain our data with a comprehensive theoretical model that clarifies several puzzling issues concerning the microscopic origin of flicker noise in graphene field-effect transistors (GraFET). PMID:21332148
NASA Astrophysics Data System (ADS)
Georgescu, IonuÅ£; Jitomirskaya, Svetlana; Mandelshtam, Vladimir A.
2013-11-01
Given a quantum many-body system, the Self-Consistent Phonons (SCP) method provides an optimal harmonic approximation by minimizing the free energy. In particular, the SCP estimate for the vibrational ground state (zero temperature) appears to be surprisingly accurate. We explore the possibility of going beyond the SCP approximation by considering the system Hamiltonian evaluated in the harmonic eigenbasis of the SCP Hamiltonian. It appears that the SCP ground state is already uncoupled to all singly- and doubly-excited basis functions. So, in order to improve the SCP result at least triply-excited states must be included, which then reduces the error in the ground state estimate substantially. For a multidimensional system two numerical challenges arise, namely, evaluation of the potential energy matrix elements in the harmonic basis, and handling and diagonalizing the resulting Hamiltonian matrix, whose size grows rapidly with the dimensionality of the system. Using the example of water hexamer we demonstrate that such calculation is feasible, i.e., constructing and diagonalizing the Hamiltonian matrix in a triply-excited SCP basis, without any additional assumptions or approximations. Our results indicate particularly that the ground state energy differences between different isomers (e.g., cage and prism) of water hexamer are already quite accurate within the SCP approximation.
Georgescu, Ionuţ Mandelshtam, Vladimir A.; Jitomirskaya, Svetlana
2013-11-28
Given a quantum many-body system, the Self-Consistent Phonons (SCP) method provides an optimal harmonic approximation by minimizing the free energy. In particular, the SCP estimate for the vibrational ground state (zero temperature) appears to be surprisingly accurate. We explore the possibility of going beyond the SCP approximation by considering the system Hamiltonian evaluated in the harmonic eigenbasis of the SCP Hamiltonian. It appears that the SCP ground state is already uncoupled to all singly- and doubly-excited basis functions. So, in order to improve the SCP result at least triply-excited states must be included, which then reduces the error in the ground state estimate substantially. For a multidimensional system two numerical challenges arise, namely, evaluation of the potential energy matrix elements in the harmonic basis, and handling and diagonalizing the resulting Hamiltonian matrix, whose size grows rapidly with the dimensionality of the system. Using the example of water hexamer we demonstrate that such calculation is feasible, i.e., constructing and diagonalizing the Hamiltonian matrix in a triply-excited SCP basis, without any additional assumptions or approximations. Our results indicate particularly that the ground state energy differences between different isomers (e.g., cage and prism) of water hexamer are already quite accurate within the SCP approximation.
Equilibrium states and ground state of two-dimensional fluid foams
Graner, F.; Jiang, Y.; Janiaud, E.; Flament, C.
2001-01-01
We study the equilibrium energies of two-dimensional (2D) noncoarsening fluid foams, which consist of bubbles with fixed areas. The equilibrium states correspond to local minima of the total perimeter. We present a theoretical derivation of energy minima; experiments with ferrofluid foams, which can be either highly distorted, locally relaxed, or globally annealed; and Monte Carlo simulations using the extended large-Q Potts model. For a dry foam with small size variance we develop physical insight and an electrostatic analogy, which enables us to (i) find an approximate value of the global minimum perimeter, accounting for (small) area disorder, the topological distribution, and physical boundary conditions; (ii) conjecture the corresponding pattern and topology: small bubbles sort inward and large bubbles sort outward, topological charges of the same signs ''repel'' while charges of the opposite signs ''attract;'' (iii) define local and global markers to determine directly from an image how far a foam is from its ground state; (iv) conjecture that, in a local perimeter minimum at prescribed topology, the pressure distribution and thus the edge curvature are unique. Some results also apply to 3D foams.
Ab initio quantum Monte Carlo calculations of ground-state properties of manganese's oxides
NASA Astrophysics Data System (ADS)
Sharma, Vinit; Krogel, Jaron T.; Kent, P. R. C.; Reboredo, Fernando A.
One of the critical scientific challenges of contemporary research is to obtain an accurate theoretical description of the electronic properties of strongly correlated systems such as transition metal oxides and rare-earth compounds, since state-of-art ab-initio methods based on approximate density functionals are not always sufficiently accurate. Quantum Monte Carlo (QMC) methods, which use statistical sampling to evaluate many-body wave functions, have the potential to answer this challenge. Owing to the few fundamental approximations made and the direct treatment of electron correlation, QMC methods are among the most accurate electronic structure methods available to date. We assess the accuracy of the diffusion Monte Carlo method in the case of rocksalt manganese oxide (MnO). We study the electronic properties of this strongly-correlated oxide, which has been identified as a suitable candidate for many applications ranging from catalysts to electronic devices. ``This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.'' Ab initio quantum Monte Carlo calculations of ground-state properties of manganese's oxides.
Robust ground state and artificial gauge in DQW exciton condensates under weak magnetic field
NASA Astrophysics Data System (ADS)
Hakioğlu, T.; Özgün, Ege; Günay, Mehmet
2014-08-01
An exciton condensate is a vast playground in studying a number of symmetries that are of high interest in the recent developments in topological condensed matter physics. In double quantum wells (DQWs) they pose highly nonconventional properties due to the pairing of non-identical fermions with a spin dependent order parameter. Here, we demonstrate a new feature in these systems: the robustness of the ground state to weak external magnetic field and the appearance of the artificial spinor gauge fields beyond a critical field strength where negative energy pair-breaking quasi particle excitations, i.e. de-excitation pockets (DX-pockets), are created in certain k regions. The DX-pockets are the Kramers symmetry broken analogs of the negative energy pockets examined in the 1960s by Sarma. They respect a disk or a shell-topology in k-space or a mixture between them depending on the magnetic field strength and the electron-hole density mismatch. The Berry connection between the artificial spinor gauge field and the TKNN number is made. This field describes a collection of pure spin vortices in real space when the magnetic field has only inplane components.
Relaxation of antihydrogen from Rydberg to ground state
Bass, Eric M.; Dubin, Daniel H. E.
2006-10-18
Atoms formed in highly-magnetized, cryogenic Penning trap plasmas, such as those used in the Athena and ATRAP antihydrogen experiments, form in the guiding-center atom regime. In this regime, the positron orbit is well described by classical guiding-center drift dynamics. Electromagnetic radiation from such atoms is minimal, and energy loss is accomplished primarily through collisions between the atom and free positrons. With Fokker-Planck theory and Monte-Carlo simulation, we calculate the mean energy change an ensemble of such atoms experiences after the atom has been formed. Using this result, we show that the bulk of atoms formed in antihydrogen experiments do not relax out of the guiding-center regime to binding energies where radiation can become important.
NASA Astrophysics Data System (ADS)
Lal, Sohan; Pandey, Sudhir K.
2016-08-01
In the present work, we investigate the applicability of the LSDA+U method in understanding the electronic and magnetic properties of a geometrically frustrated ZnV2O4 compound, where the delicate balance of electrons, lattice, orbital and spin interactions play an important role in deciding its physical properties. In the ferromagnetic solution of the compound, only one type of orbital solution is found to exist in all ranges of U studied here. However, in antiferromagnetic (AFM) phase, two types of orbital solutions, AFM(OS1) and AFM(OS2), exist for U > 3 eV. If the difference of the electronic occupancy of dxz and dyz orbitals is less than 0.25, then AFM(OS1) solution is stabilized, whereas for higher values AFM(OS2) solution is stabilized. The use of unconstrained calculations within the fully localized double counting scheme is unable to predict the AFM ground state for U ≤ 3 eV. Our results clearly suggest the importance of constrained calculations in understanding the electronic and magnetic properties of a compound, where various competing interactions are present. In the AFM solution, the orbital ground state of the compound changes with varying U, where AFM(OS1) is found to be the ground state for U ≤ 3 eV and for higher values of U, AFM(OS2) is the ground state. The analysis of the band gap suggests that the AFM(OS2) is the real ground state of the compound.
NASA Astrophysics Data System (ADS)
Chen, Zhan-Bin; Dong, Chen-Zhong; Xie, Lu-You; Jiang, Jun
2014-03-01
Electron impact excitation cross sections from the ground state and the lowest metastable state 5p56s J = 2 to the excited states of the 5p57p configuration of xenon are calculated systematically using the fully relativistic distorted wave method. Special attention is paid to the configuration interaction effects in the wave-function expansion of target states. The results are in good agreement with the recent experimental data by Jung et al. [Phys. Rev. A 80 (2009) 062708] over the measured energy range. These accurate theoretical results can be used in the modeling and diagnosis of plasmas containing xenon.
NASA Astrophysics Data System (ADS)
Li, Wei-Dong; Zhang, Yunbo; Liang, J.-Q.
2003-06-01
The energy-band structure and energy splitting due to quantum tunneling in two weakly linked Bose-Einstein condensates were calculated by using the instanton method. The intrinsic coherent properties of Bose-Josephson junction (BJJ) were investigated in terms of energy splitting. For EC/EJ≪1, the energy splitting is small and the system is globally phase coherent. In the opposite limit, EC/EJ≫1, the energy splitting is large and the system becomes phase dissipated. Our results suggest that one should investigate the coherence phenomena of BJJ in proper condition such as EC/EJ˜1.
Strategic Energy Management Plan for the Santa Ynez Band of Chumash Indians
Davenport, Lars; Smythe, Louisa; Sarquilla, Lindsey; Ferguson, Kelly
2015-03-27
This plan outlines the Santa Ynez Band of Chumash Indians’ comprehensive energy management strategy including an assessment of current practices, a commitment to improving energy performance and reducing overall energy use, and recommended actions to achieve these goals. Vision Statement The primary objective of the Strategic Energy Management Plan is to implement energy efficiency, energy security, conservation, education, and renewable energy projects that align with the economic goals and cultural values of the community to improve the health and welfare of the tribe. The intended outcomes of implementing the energy plan include job creation, capacity building, and reduced energy costs for tribal community members, and tribal operations. By encouraging energy independence and local power production the plan will promote self-sufficiency. Mission & Objectives The Strategic Energy Plan will provide information and suggestions to guide tribal decision-making and provide a foundation for effective management of energy resources within the Santa Ynez Band of Chumash Indians (SYBCI) community. The objectives of developing this plan include; Assess current energy demand and costs of all tribal enterprises, offices, and facilities; Provide a baseline assessment of the SYBCI’s energy resources so that future progress can be clearly and consistently measured, and current usage better understood; Project future energy demand; Establish a system for centralized, ongoing tracking and analysis of tribal energy data that is applicable across sectors, facilities, and activities; Develop a unifying vision that is consistent with the tribe’s long-term cultural, social, environmental, and economic goals; Identify and evaluate the potential of opportunities for development of long-term, cost effective energy sources, such as renewable energy, energy efficiency and conservation, and other feasible supply- and demand-side options; and Build the SYBCI’s capacity for
Ground states of stealthy hyperuniform potentials. II. Stacked-slider phases
NASA Astrophysics Data System (ADS)
Zhang, G.; Stillinger, F. H.; Torquato, S.
2015-08-01
Stealthy potentials, a family of long-range isotropic pair potentials, produce infinitely degenerate disordered ground states at high densities and crystalline ground states at low densities in d -dimensional Euclidean space Rd. In the previous paper in this series, we numerically studied the entropically favored ground states in the canonical ensemble in the zero-temperature limit across the first three Euclidean space dimensions. In this paper, we investigate using both numerical and theoretical techniques metastable stacked-slider phases, which are part of the ground-state manifold of stealthy potentials at densities in which crystal ground states are favored entropically. Our numerical results enable us to devise analytical models of this phase in two, three, and higher dimensions. Utilizing this model, we estimated the size of the feasible region in configuration space of the stacked-slider phase, finding it to be smaller than that of crystal structures in the infinite-system-size limit, which is consistent with our recent previous work. In two dimensions, we also determine exact expressions for the pair correlation function and structure factor of the analytical model of stacked-slider phases and analyze the connectedness of the ground-state manifold of stealthy potentials in this density regime. We demonstrate that stacked-slider phases are distinguishable states of matter; they are nonperiodic, statistically anisotropic structures that possess long-range orientational order but have zero shear modulus. We outline some possible future avenues of research to elucidate our understanding of this unusual phase of matter.
NASA Technical Reports Server (NTRS)
Goldman, A.; Bonomo, F. S.; Williams, W. J.; Murcray, D. G.; Snider, D. E.
1975-01-01
The absolute integrated intensity of the 6.2-micron band of NO2 at 40 C was determined from quantitative spectra at about 10 per cm resolution by the spectral band model technique. A value of 1430 plus or minus 300 per sq cm per atm was obtained. Individual line parameters, positions, intensities, and ground-state energies were derived, and line-by-line calculations were compared with the band model results and with the quantitative spectra obtained at about 0.5 per cm resolution.
NASA Astrophysics Data System (ADS)
Ng, L. L.; Tan, T. L.
2016-06-01
The Fourier transform infrared (FTIR) spectrum of the c-type ν8 band of 13C2HD3 was recorded for the first time at a unapodized resolution of 0.0063 cm-1 in the wavenumber region of 830-1000 cm-1. Through the fitting of a total of 1057 assigned infrared transitions using Watson's A-reduced Hamiltonian in the Ir representation, rovibrational constants for the upper state (v8 = 1) up to five quartic centrifugal distortion terms were derived for the first time with a root-mean-square (rms) deviation of 0.00073 cm-1. The band center of ν8 of 13C2HD3 was found to be 913.011021(55) cm-1. Ground state rovibrational constants up to five quartic terms of 13C2HD3 were also determined from a fit of 453 ground state combination-differences from the present infrared measurements with an rms deviation of 0.00072 cm-1 for the first time. The uncertainty of the measured infrared lines was estimated to be ±0.0012 cm-1. From the ground state rotational constants, the inertial defect of 13C2HD3 was calculated to be 0.06973(16) uÅ2, showing the high planarity of the molecule.
Speeding up DFT: A faster method for integrating band energy in SCF cycles
NASA Astrophysics Data System (ADS)
Burbidge, Matthew M.; Jorgensen, Jeremy J.; Rosenbrock, Conrad W.; Thomas, Derek C.; Hess, Bret C.; Forcade, Rodney W.; Curtarolo, Stefano; Hart, Gus L. W.
2015-03-01
Typically in SCF cycles, a ``rectangle rule'' is used on uniformly spaced points (Monk Pack meshes)1 to integrate the band energy. The use of rectangles is motivated by their fast convergence when used on the fully occupied bands of semiconductors. Unfortunately integration with rectangles is extremely inefficient for metals. This motivates the use of gauss quadrature (or other higher order methods) for integrating the band energy. As we show, however, even in the case of semiconductors where the rectangle convergence is extremely efficient, higher order methods are still more efficient. The savings in semiconductors alone are sufficient to motivate the implementation of a higher order method in current DFT codes. Even though higher order quadrature methods were discussed immediately following the original Monkhorst and Pack1 paper, we revisit the issue in light of modern DFT calculations. MMB acknowledges support by NSF (DMR-0908753). JJJ, CWR, DCT, RWF, SC, GLWH was supported by ONR (MURI N00014-13-1-0635).
NASA Astrophysics Data System (ADS)
Ma, Hui; Zhou, Haijun
2011-05-01
In this brief report we explore the energy landscapes of two spin glass models using a greedy single-spin flipping process, Gmax. The ground-state energy density of the random maximum two-satisfiability problem is efficiently approached by Gmax. The achieved energy density e(t) decreases with the evolution time t as e(t)-e(∞)=h(log10t)-z with a small prefactor h and a scaling coefficient z>1, indicating an energy landscape with deep and rugged funnel-shape regions. For the ±J Viana-Bray spin glass model, however, the greedy single-spin dynamics quickly gets trapped to a local minimal region of the energy landscape.
Antihydrogen Relaxation from High-n to Ground State.
NASA Astrophysics Data System (ADS)
Bass, E. M.; Dubin, D. H. E.
2006-10-01
We explore the rate at which magnetized, high-n Rydberg pairs formed in antihydrogen experiments relax to deep binding. While the theoretical three-body recombination rate scales favorably with low temperature (νTBRnb^3 (n v b^2 ) T-9/2), pairs form with binding energies ɛ near the (low) thermal level. Such atoms have classical drift orbits with negligible radiation. Collisions propel a cascade to deeper binding, but theory and simulation show an atom is unlikely to reach a radiating regime before it escapes the trap. However, simulations show that the energy-loss rate does not decrease as rapidly with increasing ɛ as previously expected. We also discuss the mean magnetic moment of guiding-center atoms, and energy loss from adiation at deep binding, based on the classical Larmour formula and a presumption of stochastic orbits. G. Gabrielse, N.S. Bowden, P. Oxley, et al., Phys. Rev. Lett. 89, 213401 (2002) M. Amoretti, C. Amsler, G. Bonomi, et al., Nature (London) 419, 456 (2002). ME. Glinsky and T.M. O'Neil, Phys. Fluids B 3, 1279 (1991). R. Robicheaux and J.D. Hanson, Phys. Rev. A 69, 010701 (2004). E.M. Bass and D.H.E. Dubin, Phys. Plasmas 11, 1240 (2004).
Energy band alignment in chalcogenide thin film solar cells from photoelectron spectroscopy.
Klein, Andreas
2015-04-10
Energy band alignment plays an important role in thin film solar cells. This article presents an overview of the energy band alignment in chalcogenide thin film solar cells with a particular focus on the commercially available material systems CdTe and Cu(In,Ga)Se2. Experimental results from two decades of photoelectron spectroscopy experiments are compared with density functional theory calculations taken from literature. It is found that the experimentally determined energy band alignment is in good agreement with theoretical predictions for many interfaces. These alignments, in particular the theoretically predicted alignments, can therefore be considered as the intrinsic or natural alignments for a given material combination. The good agreement between experiment and theory enables a detailed discussion of the interfacial composition of Cu(In,Ga)Se2/CdS interfaces in terms of the contribution of ordered vacancy compounds to the alignment of the energy bands. It is furthermore shown that the most important interfaces in chalcogenide thin film solar cells, those between Cu(In,Ga)Se2 and CdS and between CdS and CdTe are quite insensitive to the processing of the layers. There are plenty of examples where a significant deviation between experimentally-determined band alignment and theoretical predictions are evident. In such cases a variation of band alignment of sometimes more than 1 eV depending on interface preparation can be obtained. This variation can lead to a significant deterioration of device properties. It is suggested that these modifications are related to the presence of high defect concentrations in the materials forming the contact. The particular defect chemistry of chalcogenide semiconductors, which is related to the ionicity of the chemical bond in these materials and which can be beneficial for material and device properties, can therefore cause significant device limitations, as e.g. in the case of the CuInS2 thin film solar cells or for new
Energy band alignment in chalcogenide thin film solar cells from photoelectron spectroscopy
NASA Astrophysics Data System (ADS)
Klein, Andreas
2015-04-01
Energy band alignment plays an important role in thin film solar cells. This article presents an overview of the energy band alignment in chalcogenide thin film solar cells with a particular focus on the commercially available material systems CdTe and Cu(In,Ga)Se2. Experimental results from two decades of photoelectron spectroscopy experiments are compared with density functional theory calculations taken from literature. It is found that the experimentally determined energy band alignment is in good agreement with theoretical predictions for many interfaces. These alignments, in particular the theoretically predicted alignments, can therefore be considered as the intrinsic or natural alignments for a given material combination. The good agreement between experiment and theory enables a detailed discussion of the interfacial composition of Cu(In,Ga)Se2/CdS interfaces in terms of the contribution of ordered vacancy compounds to the alignment of the energy bands. It is furthermore shown that the most important interfaces in chalcogenide thin film solar cells, those between Cu(In,Ga)Se2 and CdS and between CdS and CdTe are quite insensitive to the processing of the layers. There are plenty of examples where a significant deviation between experimentally-determined band alignment and theoretical predictions are evident. In such cases a variation of band alignment of sometimes more than 1 eV depending on interface preparation can be obtained. This variation can lead to a significant deterioration of device properties. It is suggested that these modifications are related to the presence of high defect concentrations in the materials forming the contact. The particular defect chemistry of chalcogenide semiconductors, which is related to the ionicity of the chemical bond in these materials and which can be beneficial for material and device properties, can therefore cause significant device limitations, as e.g. in the case of the CuInS2 thin film solar cells or for new
Trends in Ground-State Entropies for Transition Metal Based Hydrogen Atom Transfer Reactions
Mader, Elizabeth A.; Manner, Virginia W.; Markle, Todd F.; Wu, Adam; Franz, James A.; Mayer, James M.
2009-03-10
SºHAT are both affected by ΔSºvib and vary significantly with the metal center involved. The close connection between ΔSºHAT and ΔSºET provides an important link between these two fields and provides a starting point from which to predict which HAT systems will have important ground-state entropy effects. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.
NASA Astrophysics Data System (ADS)
Keller, Debora; Buecheler, Stephan; Reinhard, Patrick; Pianezzi, Fabian; Bissig, Benjamin; Carron, Romain; Hage, Fredrik; Ramasse, Quentin; Erni, Rolf; Tiwari, Ayodhya N.
2016-10-01
Cu(In,Ga) Se2 (CIGS) thin film solar cells have demonstrated very high efficiencies, but still the role of nanoscale inhomogeneities in CIGS and their impact on the solar cell performance are not yet clearly understood. Due to the polycrystalline structure of CIGS, grain boundaries are very common structural defects that are also accompanied by compositional variations. In this work, we apply valence electron energy loss spectroscopy in scanning transmission electron microscopy to study the local band gap energy at a grain boundary in the CIGS absorber layer. Based on this example, we demonstrate the capabilities of a 2nd generation monochromator that provides a very high energy resolution and allows for directly relating the chemical composition and the band gap energy across the grain boundary. A band gap widening of about 20 meV is observed at the grain boundary. Furthermore, the compositional analysis by core-loss EELS reveals an enrichment of In together with a Cu, Ga and Se depletion at the same area. The experimentally obtained results can therefore be well explained by the presence of a valence band barrier at the grain boundary.
A compact ultra wideband antenna with WiMax band rejection for energy scavenging
NASA Astrophysics Data System (ADS)
Jalil, Y. E.; Kasi, B.; Chakrabarty, C. K.
2013-06-01
Radio Frequency (RF) energy harvesting has been rapidly advancing as a promising alternative to existing energy scavenging system. A well designed broadband antenna such as ultra-wideband (UWB) antenna can be used as one of the major components in an RF energy scavenging system. This paper presents a compact UWB antenna showing good impedance matching over a bandwidth of 2.8 to 11 GHz, suiTable for broadband RF energy scavenging. Nevertheless, the antenna usage in wireless communication has a limitation due to the problem of interference between UWB system and other narrowband systems. Thus, the proposed antenna is successfully designed with a single band-notched at the targeted WiMAX operating band of 3.3 to 3.6 GHz.
Optomechanical many-body cooling to the ground state using frustration
NASA Astrophysics Data System (ADS)
Fogarty, Thomás; Landa, Haggai; Cormick, Cecilia; Morigi, Giovanna
2016-08-01
We show that the vibrations of an ion Coulomb crystal can be cooled to the zero-point motion through the optomechanical coupling with a high-finesse cavity. Cooling results from the interplay between coherent scattering of cavity photons by the ions, which dynamically modifies the vibrational spectrum, and cavity losses, that dissipate motional energy. The cooling mechanism we propose requires that the length scales of the crystal and the cavity are mismatched so that the system is intrinsically frustrated, leading to the formation of defects (kinks). When the pump is strong enough, the anti-Stokes sidebands of all vibrational modes can be simultaneously driven. These dynamics can be used to prepare ground-state chains of dozens of ions within tens of milliseconds in state-of-the-art experimental setups. In addition, we identify parameter regimes of the optomechanical interactions where individual localized modes can be selectively manipulated, and monitored through the light at the cavity output. These dynamics exemplify robust quantum reservoir engineering of strongly correlated mesoscopic systems and could find applications in optical cooling of solids.
Ground State Valency and Spin Configuration of the Ni Ions in Nickelates
Petit, Leon; Egami, Takeshi; Stocks, George Malcolm; Temmerman, Walter M; Szotek, Zdzislawa
2006-01-01
The ab initio self-interaction-corrected local-spin-density approximation is used to study the electronic structure of both stoichiometric and nonstoichiometric nickelates. From total energy considerations it emerges that, in their ground state, both LiNiO2 and NaNiO2 are insulators, with the Ni ion in the Ni3+ low-spin state (t2g6eg1) configuration. It is established that a substitution of a number of Li/Na atoms by divalent impurities drives an equivalent number of Ni ions in the NiO2 layers from the Jahn-Teller (JT)-active trivalent low-spin state to the JT-inactive divalent state. We describe how the observed considerable differences between LiNiO2 and NaNiO2 can be explained through the creation of Ni2+ impurities in LiNiO2. The indications are that the random distribution of the Ni2+ impurities might be responsible for the destruction of the long-range orbital ordering in LiNiO2.
Extreme ground-state deformation of the N = Z nucleus 76Sr
NASA Astrophysics Data System (ADS)
Lemasson, A.; Iwasaki, H.; Morse, C.; Baugher, T.; Bazin, D.; Berryman, J.; Gade, A.; McDaniel, S.; Ratkiewicz, A.; Stroberg, S.; Weisshaar, D.; Wimmer, K.; Winkler, R.; Dewald, A.; Fransen, C.; Nichols, A.; Wadsworth, R.
2011-10-01
The shape of the atomic nucleus is determined by the interplay of macroscopic and microscopic effects within this quantum mechanical many-body system. Self-conjugate nuclei give an opportunity to study the role of np correlations in deformation and have attracted a great interest due to drastic shape evolution along the N = Z line. Strong ground-state deformation is expected to occur for N = Z nuclei above Z = 36 from the 2+ energy systematic as well as from theoretical predictions. Reduced transition strengths B(E2) can guide our understanding of the onset of collectivity along N = Z line. Here, we report on the first determination of B(E2; 2+ -->0+) for the N = Z = 38 nucleus 76Sr obtained from the measurement of the 2+ state lifetime using a line shape technique. 76Sr nuclei were produced at the NSCL in charge exchange reaction from fast secondary 76Rb beam. γ-rays emitted at the reaction target position were measured with the SeGA HPGe array in coincidence with reaction residues detected in the S800 spectrometer. Results will be discussed in the light of available data and theoretical predictions to provide insight into the evolution of shell structure and deformation in this region.
Sub-Ohmic spin-boson model with off-diagonal coupling: ground state properties.
Lü, Zhiguo; Duan, Liwei; Li, Xin; Shenai, Prathamesh M; Zhao, Yang
2013-10-28
We have carried out analytical and numerical studies of the spin-boson model in the sub-ohmic regime with the influence of both the diagonal and the off-diagonal coupling accounted for, via the Davydov D1 variational ansatz. While a second-order phase transition is known to be exhibited by this model in the presence of diagonal coupling only, we demonstrate the emergence of a discontinuous first order phase transition upon incorporation of the off-diagonal coupling. A plot of the ground state energy versus magnetization highlights the discontinuous nature of the transition between the isotropic (zero magnetization) state and nematic (finite magnetization) phases. We have also calculated the entanglement entropy and a discontinuity found at a critical coupling strength further supports the discontinuous crossover in the spin-boson model in the presence of off-diagonal coupling. It is further revealed via a canonical transformation approach that for the special case of identical exponents for the spectral densities of the diagonal and the off-diagonal coupling, there exists a continuous crossover from a single localized phase to doubly degenerate localized phase with differing magnetizations.
Ground states of nonlinear Choquard equations with multi-well potentials
NASA Astrophysics Data System (ADS)
Li, Shuai; Xiang, Jianlin; Zeng, Xiaoyu
2016-08-01
In this paper, we study minimizers of the Hartree-type energy functional E a ( u ) ≔ ∫ R N (" separators=" |" separators=" ∇ u ( x ) | 2 + V ( x ) |" separators=" u ( x ) | 2 " separators=" ) d x - /a p ∫ R N (" separators=" I α ∗ |" separators=" u ( x ) | p " separators=" ) |" separators=" u ( x ) | p d x , a ≥ 0 under the mass constraint ∫ R N |" separators=" u | 2 d x = 1 , where p = /N + α + 2 N with α ∈ (0, N) for N ≥ 2 is the mass critical exponent. Here Iα denotes the Riesz potential and the trapping potential 0 ≤ V ( x ) ∈ Lloc ∞ ( R N ) satisfies lim |" separators=" x | → ∞ V ( x ) = ∞ . We prove that minimizers exist if and only if a satisfies a < a ∗ = ↑"separators=" Q ↑ 2 2 ( p - 1 ) , where Q is a positive radially symmetric ground state of - Δ u + u = ( I α ∗ |" separators=" u | p ) |" separators=" u | p - 2 u in ℝN. The uniqueness of positive minimizers holds if a > 0 is small enough. The blow-up behavior of positive minimizers as a↗a∗ is also derived under some general potentials. Especially, we prove that minimizers must blow up at the central point of the biggest inscribed sphere of the set Ω ≔ {x ∈ ℝN, V(x) = 0} if |" separators=" Ω | > 0 .
Rotational bands in neutron-rich {sup 169,171,172}Er
Wu, C.Y.; Cline, D.; Simon, M.W.; Teng, R.; Vetter, K.; Carpenter, M.P.; Janssens, R.V.F.; Wiedenhoever, I.
2004-07-01
The neutron-rich {sup 169,171,172}Er nuclei were populated by few-neutron transfer reactions between {sup 170}Er and {sup 238}U at a near barrier energy. The spectroscopy of these Er isotopes was studied using prompt {gamma} rays correlated with delayed transitions or events involving at least three prompt transitions. The ground-state band of {sup 172}Er was populated up to spin 22{sup +} at an excitation energy of 5528 keV. Rotational bands built on the 1/2{sup -}[521], 5/2{sup -}[512], and 7/2{sup +}[633] neutron configurations in {sup 169,171}Er were extended to substantially higher spins than previously known. The signature splitting observed in these rotational bands is addressed within the framework of the particle-rotor model in terms of triaxiality and Coriolis attenuation. The signature inversion observed in the 5/2{sup -}[512] band is well reproduced by including the triaxial degree of freedom in the calculation. Attenuating the Coriolis interaction in the calculation is found to be necessary to reproduce the signature splitting observed in the 7/2{sup +}[633] band. A similar Coriolis attenuation also is needed to account for the signature splitting as well as the B(M1)/B(E2) ratios in the 7/2{sup +}[633] ground-state band in the neighboring N=99 isotones, {sup 167}Er and {sup 169}Yb.
Gaulin, B. D.; Kermarrec, E.; Dahlberg, M. L.; Matthews, M. J.; Bert, F.; Zhang, J.; Mendels, P.; Fritsch, K.; Granroth, G. E.; Jiramongkolchai, P.; et al
2015-06-01
Solid-solutions of the "soft" quantum spin ice pyrochlore magnets Tb2B2O7 with B=Ti and Sn display a novel magnetic ground state in the presence of strong B-site disorder, characterized by a low susceptibility and strong spin fluctuations to temperatures below 0.1 K. These materials have been studied using ac-susceptibility and muSR techniques to very low temperatures, and time-of-flight inelastic neutron scattering techniques to 1.5 K. Remarkably, neutron spectroscopy of the Tb3+ crystal field levels appropriate to at high B-site mixing (0.5 < x < 1.5 in Tb2Sn2-xTixO7) reveal that the doublet ground and first excited states present as continua in energy,more » while transitions to singlet excited states at higher energies simply interpolate between those of the end members of the solid solution. The resulting ground state suggests an extreme version of a random-anisotropy magnet, with many local moments and anisotropies, depending on the precise local configuration of the six B sites neighboring each magnetic Tb3+ ion.« less
Electronic excitation of ground state atoms by collision with heavy gas particles
NASA Technical Reports Server (NTRS)
Hansen, C. Frederick
1993-01-01
Most of the important chemical reactions which occur in the very high temperature air produced around space vehicles as they enter the atmosphere were investigated both experimentally and theoretically, to some extent at least. One remaining reaction about which little is known, and which could be quite important at the extremely high temperatures that will be produced by the class of space vehicles now contemplated - such as the AOTV - is the excitation of bound electron states due to collisions between heavy gas particles. Rates of electronic excitation due to free electron collisions are known to be very rapid, but because these collisions quickly equilibrate the free and bound electron energy, the approach to full equilibrium with the heavy particle kinetic energy will depend primarily on the much slower process of bound electron excitation in heavy particle collisions and the subsequent rapid transfer to free electron energy. This may be the dominant mechanism leading to full equilibrium in the gas once the dissociation process has depleted the molecular states so the transfer between molecular vibrational energy and free electron energy is no longer available as a channel for equilibration of free electron and heavy particle kinetic energies. Two mechanisms seem probable in electronic excitation by heavy particle impact. One of these is the collision excitation and deexcitation of higher electronic states which are Rydberg like. A report, entitled 'Semi-Classical Theory of Electronic Excitation Rates', was submitted previously. This presented analytic expressions for the transition probabilities, assuming that the interaction potential is an exponential repulsion with a perturbation ripple due to the dipole-induced dipole effect in the case of neutral-neutral collisions, and to the ion-dipole interaction in the case of ion-neutral collisions. However the above may be, there is little doubt that excitation of ground state species by collision occurs at the
NASA Astrophysics Data System (ADS)
Yulianto, Yacobus; Su'ud, Zaki
2016-08-01
It has been performed the nuclear ground state properties investigation of 232Th and 238U using Skyrme interaction. The local density, the kinetic energy density, and the spin-orbit density for proton and neutron have been calculated using Extended-Thomas-Fermi approach method. Then the calculation results have been compared with Skyrme-Hartree-Fock results (using HAFOMN and HFBRAD codes). Total energy calculations obtained from this research are -1792.973947 MeV (for 232Th) deviated 0.29244% from experiment energy and -1761.519459 MeV (for 238U) deviated 0.48369% from experiment energy. The distribution profiles of local density and local potential for 232Th and 238U are quite similar with Skyrme- Hartree-Fock results. It is indicated that Skyrme-Extended-Thomas-Fermi method can be used to study the nuclear ground state properties, especially even nuclei.
NASA Astrophysics Data System (ADS)
Rodríguez-Guzmán, R.; Jiménez-Hoyos, Carlos A.; Scuseria, Gustavo E.
2014-05-01
The few determinant (FED) approximation introduced in our previous work [Phys. Rev. B 87, 235129 (2013)], 10.1103/PhysRevB.87.235129 is used to describe the ground state, characterized by well-defined spin and space group symmetry quantum numbers as well as doping fractions Ne/Nsites, of one-dimensional Hubbard lattices with nearest-neighbor hopping and periodic boundary conditions. Within this multireference scheme, each ground state is expanded in a given number of nonorthogonal and variationally determined symmetry-projected configurations. The results obtained for the ground-state and correlation energies of half-filled and doped lattices with 30, 34, and 50 sites compare well with the exact Lieb-Wu solutions as well as with those obtained with other state-of-the-art approximations. The structure of the intrinsic symmetry-broken determinants resulting from the variational procedure is interpreted in terms of solitons whose translational and breathing motions can be regarded as basic units of quantum fluctuations. It is also shown that in the case of doped one-dimensional lattices, a part of such fluctuations can also be interpreted in terms of polarons. In addition to momentum distributions, both spin-spin and density-density correlation functions are studied as functions of doping. The spectral functions and density of states, computed with an ansatz whose quality can be well controlled by the number of symmetry-projected configurations used to approximate the Ne±1 electron systems, display features beyond a simple quasiparticle distribution, as well as spin-charge separation trends.
Theoretical rovibrational line intensities in the electronic ground state of ozone
NASA Astrophysics Data System (ADS)
Diehr, Matthieu; Rosmus, Pavel; Carter, Stuart; Knowles, Peter J.
2004-01-01
First-principles calculations of absolute line intensities and rovibrational energies of ozone (16O3) are reported using potential energy and electric dipole moment functions calculated by the internally contracted MRCI approach. The rovibrational energies and eigenfunctions (up to about 8500 cm-1 and J = 64) were obtained variationally with an exact Hamiltonian in internal valence coordinates. More than 4.8 × 106 electric dipole transition matrix elements were calculated for the absolute rovibrational line intensities. They are compared with the values of the HITRAN database. The purely rotational absolute line intensities in the (000) state and the rovibrational intensities for the (001)-(000) band agree to within about 0.3 to 1% for the (010)-(000) band to within about 3 to 4%. Excellent agreement with experiment is also achieved for low-lying overtone and combination bands. Inconsistencies are found for the (100)-(000) band overlapping with the antisymmetric stretching fundamental and also for the (002)-(000) antisymmetric stretching overtone. The generated dipole moment function can be used for predicting the absorption intensities in any of the heavier isotopomers, hot bands or the rates of spontaneous emission.
Inaoka, Takeshi Furukawa, Takuro; Toma, Ryo; Yanagisawa, Susumu
2015-09-14
By means of a hybrid density-functional method, we investigate the tensile-strain effect of inducing the indirect-to-direct band-gap transition and reducing the band-gap energy of Ge. We consider [001], [111], and [110] uniaxial tensility and (001), (111), and (110) biaxial tensility. Under the condition of no normal stress, we determine both normal compression and internal strain, namely, relative displacement of two atoms in the primitive unit cell, by minimizing the total energy. We identify those strain types which can induce the band-gap transition, and evaluate the critical strain coefficient where the gap transition occurs. Either normal compression or internal strain operates unfavorably to induce the gap transition, which raises the critical strain coefficient or even blocks the transition. We also examine how each type of tensile strain decreases the band-gap energy, depending on its orientation. Our analysis clearly shows that synergistic operation of strain orientation and band anisotropy has a great influence on the gap transition and the gap energy.
Stability and related properties of vacua and ground states
Wreszinski, Walter F. Jaekel, Christian D.
2008-02-15
We consider the formal non-relativistic limit (nrl) of the :{phi}{sup 4}:{sub s+1} relativistic quantum field theory (rqft), where s is the space dimension. Following the work of R. Jackiw [R. Jackiw, in: A. Ali, P. Hoodbhoy (Eds.), Beg Memorial Volume, World Scientific, Singapore, 1991], we show that, for s = 2 and a given value of the ultraviolet cutoff {kappa}, there are two ways to perform the nrl: (i) fixing the renormalized mass m{sup 2} equal to the bare mass m{sub 0}{sup 2}; (ii) keeping the renormalized mass fixed and different from the bare mass m{sub 0}{sup 2}. In the (infinite-volume) two-particle sector the scattering amplitude tends to zero as {kappa} {yields} {infinity} in case (i) and, in case (ii), there is a bound state, indicating that the interaction potential is attractive. As a consequence, stability of matter fails for our boson system. We discuss why both alternatives do not reproduce the low-energy behaviour of the full rqft. The singular nature of the nrl is also nicely illustrated for s = 1 by a rigorous stability/instability result of a different nature.
Potential energy surface and vibrational band origins of the triatomic lithium cation
NASA Astrophysics Data System (ADS)
Searles, Debra J.; Dunne, Simon J.; von Nagy-Felsobuki, Ellak I.
The 104 point CISD Li +3 potential energy surface and its analytical representation is reported. The calculations predict the minimum energy geometry to be an equilateral triangle of side RLiLi = 3.0 Å and of energy - 22.20506 E h. A fifth-order Morse—Dunham type analytical force field is used in the Carney—Porter normal co-ordinate vibrational Hamiltonian, the corresponding eigenvalue problem being solved variationally using a 560 configurational finite-element basis set. The predicted assignment of the vibrational band origins is in accord with that reported for H +3. Moreover, for 6Li +3 and 7Li +3 the lowest i.r. accessible band origin is the overlineν0,1,±1 predicted to be at 243.6 and 226.0 cm -1 respectively.
Boron: do we know the ground state structure?
NASA Astrophysics Data System (ADS)
Ogitsu, Tadashi
2006-03-01
Boron is only the fifth element in the periodic table, having a simple electronic configuration, yet, it is known to form one of the most complicated crystal structures, β-rhombohedral structure. Up to date, the best estimate on the number of atoms in its hexagonal unit cell is 320.1, not even an integer number. The key concept to understand its complexity is covalency and electron deficiency: It does not have enough valence electrons to form a simple covalent crystal, like carbon or silicon. Instead it forms a complicated packing of icosahedrons. The structural model of β-boron was developed in the 1960s based on X-ray experiment. Although this model structure captures the most of the structural characteristics of β-boron, it has a crucial pitfall; the number of atoms per cell estimated by X-ray experiment does not agree with the number of atoms estimated by the pycnometric density. In 1988, Slack et al. discovered four more POS, by which the discrepancy in the number of atoms is reconciled [J. of Solid State Chem. 76, 52 (1988)]. There still remains an unanswered question; how are these POS atoms configured? Is it completely random? Or there is some kind of order as it has been suggested in Slack’s paper? A major challenge here is the astronomical number of possible configurations, roughly 150 million even for the irreducible cell. We tackle this problem using ab-initio simulated annealing coupled with a Lattice Model Monte Carlo simulated annealing. Our results reveal that the stable structure, indeed, has a certain type of correlation in its POS configuration. More detail on the structural property and its impact on electronic property of β-boron will be discussed at the presentation. This work was performed under the auspices of the U.S. Dept. of Energy at the University of California/ LLNL under contract no. W-7405-Eng-48.
Fragile surface zero-energy flat bands in three-dimensional chiral superconductors
NASA Astrophysics Data System (ADS)
Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi
2015-12-01
We study surface zero-energy flat bands in three-dimensional chiral superconductors with pz(px+i py) ν -wave pairing symmetry (ν is a nonzero integer), based on topological arguments and tunneling conductance. It is shown that the surface flat bands are fragile against (i) the surface misorientation and (ii) the surface Rashba spin-orbit interaction. The fragility of (i) is specific to chiral SCs, whereas that of (ii) happens for general odd-parity SCs. We demonstrate that these flat-band instabilities vanish or suppress a zero-bias conductance peak in a normal/insulator/superconductor junction, which behavior is clearly different from high-Tc cuprates and noncentrosymmetric superconductors. By calculating the angle-resolved conductance, we also discuss a topological surface state associated with the coexistence of line and point nodes.
NASA Astrophysics Data System (ADS)
Antoine, Xavier; Tang, Qinglin; Zhang, Yong
2016-11-01
In this paper, we propose some efficient and robust numerical methods to compute the ground states and dynamics of Fractional Schrödinger Equation (FSE) with a rotation term and nonlocal nonlinear interactions. In particular, a newly developed Gaussian-sum (GauSum) solver is used for the nonlocal interaction evaluation [31]. To compute the ground states, we integrate the preconditioned Krylov subspace pseudo-spectral method [4] and the GauSum solver. For the dynamics simulation, using the rotating Lagrangian coordinates transform [14], we first reformulate the FSE into a new equation without rotation. Then, a time-splitting pseudo-spectral scheme incorporated with the GauSum solver is proposed to simulate the new FSE. In parallel to the numerical schemes, we also prove some existence and nonexistence results for the ground states. Dynamical laws of some standard quantities, including the mass, energy, angular momentum and the center of mass, are stated. The ground states properties with respect to the fractional order and/or rotating frequencies, dynamics involving decoherence and turbulence together with some interesting phenomena are reported.
Ground-state properties of linear-exchange quantum spin models
NASA Astrophysics Data System (ADS)
Danu, Bimla; Kumar, Brijesh; Pai, Ramesh V.
2012-10-01
We study a class of one-dimensional antiferromagnetic quantum spin-1/2 models using DMRG. The exchange interaction in these models decreases linearly with the separation between the spins, Jij = R - |i - j| for |i - j| < R, where R is a positive integer ⩾2. For |i - j| ⩾ R, the interaction is zero. It is known that all the odd-R models have the same exact dimer ground state as the Majumdar-Ghosh (MG) model. In fact, R = 3 is the MG model. However, for an even R, the exact ground state is not known in general, except for R = 2 (the integrable nearest-neighbor Heisenberg chain) and the asymptotic limit of R in which the MG dimer state emerges as the exact ground state. Therefore, we numerically study the ground-state properties of the finite even-R ≠ 2 models, particularly for R = 4, 6 and 8. We find that, unlike R = 2, the higher even-R models are spin-gapped, and exhibit robust dimer order of the MG type in the ground state. The spin-spin correlations decay rapidly to zero, albeit showing weak periodic revivals.
Precision molecular spectroscopy for ground state transfer of molecular quantum gases.
Danzl, Johann G; Mark, Manfred J; Haller, Elmar; Gustavsson, Mattias; Bouloufa, Nadia; Dulieu, Olivier; Ritsch, Helmut; Hart, Russell; Nägerl, Hanns-Christoph
2009-01-01
One possibility for the creation of ultracold, high phase space density quantum gases of molecules in the rovibronic ground state relies on first associating weakly-bound molecules from quantum-degenerate atomic gases on a Feshbach resonance and then transferring the molecules via several steps of coherent two-photon stimulated Raman adiabatic passage (STIRAP) into the rovibronic ground state. Here, in ultracold samples of Cs2 Feshbach molecules produced out of ultracold samples of Cs atoms, we observe several optical transitions to deeply-bound rovibrational levels of the excited 0(u)+ molecular potentials with high resolution. At least one of these transitions, although rather weak, allows efficient STIRAP transfer into the deeply-bound vibrational level (see text for symbols)v = 73 > of the singlet X1 sigma(g)+ ground state potential, as recently demonstrated (J. G. Danzl, E. Haller, M. Gustavsson, M. J. Mark, R. Hart, N. Bouloufa, O. Dulieu, H. Ritsch, and H.-C. Nägerl, Science, 2008, 321, 1062). From this level, the rovibrational ground state (see text for symbols)v = 0, J = 0 > can be reached with one more transfer step. In total, our results show that coherent ground state transfer for Cs2 is possible using a maximum of two successive two-photon STIRAP processes or one single four-photon STIRAP process. PMID:20151549
Creation of an Ultracold Gas of Ground-State Dipolar 23Na 87 Molecules
NASA Astrophysics Data System (ADS)
Guo, Mingyang; Zhu, Bing; Lu, Bo; Ye, Xin; Wang, Fudong; Vexiau, Romain; Bouloufa-Maafa, Nadia; Quéméner, Goulven; Dulieu, Olivier; Wang, Dajun
2016-05-01
We report the successful production of an ultracold sample of absolute ground-state 23Na 87Rb molecules. Starting from weakly bound Feshbach molecules formed via magnetoassociation, the lowest rovibrational and hyperfine level of the electronic ground state is populated following a high-efficiency and high-resolution two-photon Raman process. The high-purity absolute ground-state samples have up to 8000 molecules and densities of over 1011 cm-3 . By measuring the Stark shifts induced by external electric fields, we determined the permanent electric dipole moment of the absolute ground-state 23Na 87Rb and demonstrated the capability of inducing an effective dipole moment over 1 D. Bimolecular reaction between ground-state 23Na 87Rb molecules is endothermic, but we still observed a rather fast decay of the molecular sample. Our results pave the way toward investigation of ultracold molecular collisions in a fully controlled manner and possibly to quantum gases of ultracold bosonic molecules with strong dipolar interactions.
Creation of an Ultracold Gas of Ground-State Dipolar ^{23}Na^{87}Rb Molecules.
Guo, Mingyang; Zhu, Bing; Lu, Bo; Ye, Xin; Wang, Fudong; Vexiau, Romain; Bouloufa-Maafa, Nadia; Quéméner, Goulven; Dulieu, Olivier; Wang, Dajun
2016-05-20
We report the successful production of an ultracold sample of absolute ground-state ^{23}Na^{87}Rb molecules. Starting from weakly bound Feshbach molecules formed via magnetoassociation, the lowest rovibrational and hyperfine level of the electronic ground state is populated following a high-efficiency and high-resolution two-photon Raman process. The high-purity absolute ground-state samples have up to 8000 molecules and densities of over 10^{11} cm^{-3}. By measuring the Stark shifts induced by external electric fields, we determined the permanent electric dipole moment of the absolute ground-state ^{23}Na^{87}Rb and demonstrated the capability of inducing an effective dipole moment over 1 D. Bimolecular reaction between ground-state ^{23}Na^{87}Rb molecules is endothermic, but we still observed a rather fast decay of the molecular sample. Our results pave the way toward investigation of ultracold molecular collisions in a fully controlled manner and possibly to quantum gases of ultracold bosonic molecules with strong dipolar interactions. PMID:27258875
Search for two-{gamma} sum-energy peaks in the decay out of superdeformed bands
Blumenthal, D.; Khoo, T.L.; Lauritsen, T.
1995-08-01
The spectrum of {gamma}rays decaying out of the superdeformed (SD) band in {sup 192}Hg has a quasicontinuous distribution. Whereas methods to construct level schemes from discrete lines in coincidence spectra are well established, new techniques must still be developed to extract information from coincidences involving quasicontinuous {gamma}rays. From an experiment using Eurogam, we obtained impressively clean 1- and 2-dimensional {gamma} spectra from pairwise or single gates, respectively, on the transitions of the SD band in {sup 192}Hg. We investigated methods to exploit the 2-dimensional quasicontinuum spectra coincident with the SD band to determine the excitation energy of the SD band above the normal yrast line. No strong peaks were observed in the 2-{gamma} sum spectra; only candidates of peaks at a 2-3 {sigma} level were found. This suggests that 2-{gamma} decay is not the dominant decay branch out of SD bands, consistent with the observed multiplicity of 3.2. We shall next search for peaks in sum-spectra of 3 {gamma}s.
The C-Band accelerating structures for SPARC photoinjector energy upgrade
NASA Astrophysics Data System (ADS)
Alesini, D.; Boni, R.; Di Pirro, G.; Di Raddo, R.; Ferrario, M.; Gallo, A.; Lollo, V.; Marcellini, F.; Palumbo, L.; Spizzo, V.; Mostacci, A.; Campogiani, G.; Persichelli, S.; Enomoto, A.; Higo, T.; Kakihara, K.; Kamitani, T.; Matsumoto, S.; Sugimura, T.; Yokoyama, K.; Verdú-Andrés, S.
2013-05-01
The use of C-Band structures for electron acceleration and production of high quality beams has been proposed and adopted in several linac projects all over the world. The two main projects that adopted such type of structures are the Japanese Free Electron Laser (FEL) project in Spring-8 and the SwissFEL project at Paul Scherrer Institute (PSI). Also the energy upgrade of the SPARC photo-injector at LNF-INFN (Italy) from 150 to more than 240 MeV will be done by replacing a low gradient S-Band accelerating structure with two C-band structures. The structures are Traveling Wave (TW) and Constant Impedance (CI), have symmetric axial input couplers and have been optimized to work with a SLED RF input pulse. The paper presents the design criteria of the structures, the realization procedure and the low and high power RF test results on a prototype. The high power tests have been carried out by the Frascati INFN Laboratories in close collaboration with the Japanese Laboratory KEK. Experimental results confirmed the feasibility of the operation of the prototype at 50 MV/m with about 10-6 breakdowns per pulse per meter. Such high gradients have not been reached before in C-Band systems and demonstrated the possibility to use C-band accelerators, if needed, at such high field level. The results of the internal inspection of the structure after the high power test are also presented.
From ground state to fission fragments: A complex, multi-dimensional multi-path problem
Moeller, P.; Nix, J.R.; Swiatecki, W.J.
1992-03-01
Experimental results on the fission properties of nuclei close to {sup 264}Fm show sudden and large changes with a change of only one or two neutrons or protons. The nucleus {sup 258}Fm, for instance, undergoes symmetric fission with a half-life of about 0.4 ms and a kinetic-energy distribution peaked at about 235 MeV whereas {sup 256}Fm undergoes asymmetric fission with a half-life of about 3 h and a kinetic-energy distribution peaked at about 200 MeV. Qualitatively, these sudden changes have been postulated to be due to the emergence of fragment shells in symmetric-fission products close to {sup 132}Sn. Here we present a quantitative calculation that shows where high-kinetic-energy symmetric fusion occurs and why it is associated with a sudden and large decrease in fission half-lives. We base our study on calculations of potential-energy surfaces in the macroscopic-microscopic model and a semi-empirical model for the nuclear inertia. We use the three-quadratic-surface parameterization to generate the shapes for which the potential-energy surfaces are calculated. The use of this parameterization and the use of the finite-range macroscopic model allows for the study of two touching spheres and similar shapes. Since these shapes are thought to correspond to the scission shapes for the high-kinetic-energy events it is of crucial importance that a continuous sequence of shapes leading from the nuclear ground state to these configurations can be studied within the framework of the model. We present the results of the calculations in terms of potential-energy surfaces and fission half-lives for heavy even nuclei. The surfaces are displayed in the form of contour diagrams as functions of two moments of the shape. They clearly show the appearance of a second fission valley, which leads to scission configurations close to tow touching spheres, for fissioning systems in the vicinity of {sup 264}Fm.
From ground state to fission fragments: A complex, multi-dimensional multi-path problem
Moeller, P. ); Nix, J.R. ); Swiatecki, W.J. )
1992-01-01
Experimental results on the fission properties of nuclei close to {sup 264}Fm show sudden and large changes with a change of only one or two neutrons or protons. The nucleus {sup 258}Fm, for instance, undergoes symmetric fission with a half-life of about 0.4 ms and a kinetic-energy distribution peaked at about 235 MeV whereas {sup 256}Fm undergoes asymmetric fission with a half-life of about 3 h and a kinetic-energy distribution peaked at about 200 MeV. Qualitatively, these sudden changes have been postulated to be due to the emergence of fragment shells in symmetric-fission products close to {sup 132}Sn. Here we present a quantitative calculation that shows where high-kinetic-energy symmetric fusion occurs and why it is associated with a sudden and large decrease in fission half-lives. We base our study on calculations of potential-energy surfaces in the macroscopic-microscopic model and a semi-empirical model for the nuclear inertia. We use the three-quadratic-surface parameterization to generate the shapes for which the potential-energy surfaces are calculated. The use of this parameterization and the use of the finite-range macroscopic model allows for the study of two touching spheres and similar shapes. Since these shapes are thought to correspond to the scission shapes for the high-kinetic-energy events it is of crucial importance that a continuous sequence of shapes leading from the nuclear ground state to these configurations can be studied within the framework of the model. We present the results of the calculations in terms of potential-energy surfaces and fission half-lives for heavy even nuclei. The surfaces are displayed in the form of contour diagrams as functions of two moments of the shape. They clearly show the appearance of a second fission valley, which leads to scission configurations close to tow touching spheres, for fissioning systems in the vicinity of {sup 264}Fm.
Huang, C H; Kaiser, R I; Chang, A H H
2009-11-12
The bimolecular reaction of ground state cyano radical with propylene under the condition of single collision is investigated by combining ab initio electronic structure calculations for predicting reaction paths and RRKM theory to yield rate constant for each path. The isomerization and dissociation channels for each of the seven collision complexes are characterized by utilizing the unrestricted B3LYP/cc-pVTZ level of theory and the CCSD(T)/cc-pVTZ calculations. Sifting with the facilitation of RRKM rate constants through web of ab initio paths composed of 8 collision complexes, 37 intermediates, and 12 H-, 23 H(2)-, 3 HCN-, and 4 CH(3)-dissociated products, we identify the most probable paths down to 7-9 species at collisions energies of 0 and 5 kcal/mol as the reaction mechanisms. The rate equations of the reaction mechanisms are solved numerically such that the concentration evolutions for all species involved are obtained. This study predicts that CN + C(2)H(3)CH(3) reaction via any of the seven collision complex, c1-c5, c7, and c8, would produce p1(CH(3)CHCHCN) + H, p2(CH(2)CHCH(2)CN) + H, and mostly p43(vinyl cyanide) + CH(3) for collision energy within 0-5 kcal/mol. In addition to the insertion mechanism through collision complex, the direct H-abstraction of propylene by CN radical might occur. Our investigation indicates that the barrierless and exoergic CN(X(2)Sigma(+)) + C(2)H(3)CH(3)(X(1)A') reaction would be an efficient route for the p1, p2, and p43, and likely HCN formation in cold molecular clouds and in the atmosphere of Saturn's satellite Titan.
Ground States of Random Spanning Trees on a D-Wave 2X
NASA Astrophysics Data System (ADS)
Hall, J. S.; Hobl, L.; Novotny, M. A.; Michielsen, Kristel
The performances of two D-Wave 2 machines (476 and 496 qubits) and of a 1097-qubit D-Wave 2X were investigated. Each chip has a Chimera interaction graph calG . Problem input consists of values for the fields hj and for the two-qubit interactions Ji , j of an Ising spin-glass problem formulated on calG . Output is returned in terms of a spin configuration {sj } , with sj = +/- 1 . We generated random spanning trees (RSTs) uniformly distributed over all spanning trees of calG . On the 476-qubit D-Wave 2, RSTs were generated on the full chip with Ji , j = - 1 and hj = 0 and solved one thousand times. The distribution of solution energies and the average magnetization of each qubit were determined. On both the 476- and 1097-qubit machines, four identical spanning trees were generated on each quadrant of the chip. The statistical independence of these regions was investigated. In another study, on the D-Wave 2X, one hundred RSTs with random Ji , j ∈ { - 1 , 1 } and hj = 0 were generated on the full chip. Each RST problem was solved one hundred times and the number of times the ground state energy was found was recorded. This procedure was repeated for square subgraphs, with dimensions ranging from 7 ×7 to 11 ×11. Supported in part by NSF Grants DGE-0947419 and DMR-1206233. D-Wave time provided by D-Wave Systems and by the USRA Quantum Artificial Intelligence Laboratory Research Opportunity.
Accurate intermolecular ground state potential of the Ne-N2 van der Waals complex.
Munteanu, Cristian R; López Cacheiro, Javier; Fernández, Berta
2004-05-15
Ab initio ground state potential energy surfaces are obtained from interaction energies calculated with the coupled cluster singles and doubles model including connected triples corrections [CCSD(T)] and the aug-cc-pVXZ (X=5,Q,T,D) basis sets augmented with two different sets of midbond functions (denoted 33221 and 33211). The aug-cc-pV5Z-33221 surface is characterized by a T-shaped 49.5 cm(-1) minimum at Re=3.38 Angstroms and a linear saddle point at 3.95 Angstroms with De=36.6 cm(-1). These results agree well with the values provided by the accurate semiempirical potentials available. The rovibronic spectroscopic properties are determined and compared to the available experimental data and previous theoretical results. We study the basis set convergence of the intermolecular potentials and the rotational frequencies. The aug-cc-pVTZ basis sets provide reasonable binding parameters, but seem not to be converged enough for the evaluation of the microwave spectra. The aug-cc-pVQZ basis sets considerably improve the triple zeta results. The differences between the results obtained with the aug-cc-pVTZ-33221 basis set surface and those with the aug-cc-pVQZ-33221 are smaller than those of the corresponding bases with the set of 33211 midbond functions. The aug-cc-pVQZ surfaces are close to the aug-cc-pV5Z, that are expected to be close to convergence. With our best surfaces the errors in the frequencies with respect to the accurate experimental results go down to 0.6%.
Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet
Fu, Mingxuan; Imai, Takahashi; Han, Tian -Heng; Lee, Young S.
2015-11-06
Here, the kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χkagome, deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with themore » magnetic field dependence of χkagome that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.« less
Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet.
Fu, Mingxuan; Imai, Takashi; Han, Tian-Heng; Lee, Young S
2015-11-01
The kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χ(kagome), deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with the magnetic field dependence of χ(kagome) that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap. PMID:26542565
Ground State Properties of the 1/2 Flux Harper Hamiltonian
NASA Astrophysics Data System (ADS)
Kennedy, Colin; Burton, William Cody; Chung, Woo Chang; Ketterle, Wolfgang
2015-05-01
The Harper Hamiltonian describes the motion of charged particles in an applied magnetic field - the spectrum of which exhibits the famed Hofstadter's butterfly. Recent advances in driven optical lattices have made great strides in simulating nontrivial Hamiltonians, such as the Harper model, in the time-averaged sense. We report on the realization of the ground state of bosons in the Harper Hamiltonian for 1/2 flux per plaquette utilizing a tilted two-dimensional lattice with laser assisted tunneling. We detail progress in studying various ground state properties of the 1/2 flux Harper Hamiltonian including ground state degeneracies, gauge-dependent observables, effects of micromotion, adiabatic loading schemes, and emergence and decay of coherence. Additionally, we describe prospects for flux rectification using a period-tripled superlattice and generalizations to three dimensions. MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, Department of Physics, Massachusetts Institute of Technology.
2013-01-01
We investigate the nature of the S* excited state in carotenoids by performing a series of pump–probe experiments with sub-20 fs time resolution on spirilloxanthin in a polymethyl-methacrylate matrix varying the sample temperature. Following photoexcitation, we observe sub-200 fs internal conversion of the bright S2 state into the lower-lying S1 and S* states, which in turn relax to the ground state on a picosecond time scale. Upon cooling down the sample to 77 K, we observe a systematic decrease of the S*/S1 ratio. This result can be explained by assuming two thermally populated ground state isomers. The higher lying one generates the S* state, which can then be effectively frozen out by cooling. These findings are supported by quantum chemical modeling and provide strong evidence for the existence and importance of ground state isomers in the photophysics of carotenoids. PMID:23577754
Exploring chaos in the Dicke model using ground-state fidelity and Loschmidt echo.
Bhattacharya, Utso; Dasgupta, Sayak; Dutta, Amit
2014-08-01
We study the quantum critical behavior of the Dicke Hamiltonian with finite number of atoms and explore the signature of quantum chaos using measures like the ground-state fidelity and the Loschmidt echo and the time-averaged Loschmidt echo. We show that these quantities clearly point to the classically chaotic nature of the system in the superradiant (SR) phase. While the ground-state fidelity shows aperiodic oscillations as a function of the coupling strength, the echo shows aperiodic oscillations in time and decays rapidly when the system is in the SR phase. We clearly demonstrate how the time-averaged value of the echo already incorporates the information about the ground-state fidelity and stays much less than unity, indicating the classically chaotic nature of the model in the SR phase.
NASA Astrophysics Data System (ADS)
Sebastian, Suchitra
2015-03-01
Over the last few years, evidence has gradually built for a charge ordered normal ground state in the underdoped region of the cuprate high temperature superconductors. I will address the electronic structure of the normal ground state of the underdoped cuprates as accessed by quantum oscillations, and relate it to complementary measurements by other experimental techniques. The interplay of the charge ordered ground state with the antinodal gapped pseudogap state, and overarching magnetic and superconducting correlations will be further explored. This work was performed in collaboration with N. Harrison, G. G. Lonzarich, B. J. Ramshaw, B. S. Tan, P. A. Goddard, F. F. Balakirev, C. H. Mielke, R. Liang, D. A. Bonn, and W. N. Hardy
Ground-state features in the THz spectra of molecular clusters of β-HMX.
Huang, Lulu; Shabaev, Andrew; Lambrakos, Samuel G; Massa, Lou
2012-10-01
We present calculations of absorption spectra arising from molecular vibrations at THz frequencies for molecular clusters of the explosive HMX using density functional theory (DFT). The features of these spectra can be shown to follow from the coupling of vibrational modes. In particular, the coupling among ground-state vibrational modes provides a reasonable molecular-level interpretation of spectral features associated with the vibrational modes of molecular clusters. THz excitation from the ground state is associated with frequencies that characteristically perturb molecular electronic states, in contrast to frequencies, which are usually substantially above the mid-infrared (mid-IR) range, that can induce appreciable electronic-state transition. Owing to this characteristic of THz excitation, one is able to make a direct association between local oscillations about ground-state minima of molecules, either isolated or comprising a cluster, and THz absorption spectra. The DFT software program GAUSSIAN was used for the calculations of the absorption spectra presented here.
Energy-band diagram configuration of Al2O3/oxygen-terminated p-diamond metal-oxide-semiconductor
NASA Astrophysics Data System (ADS)
Maréchal, A.; Aoukar, M.; Vallée, C.; Rivière, C.; Eon, D.; Pernot, J.; Gheeraert, E.
2015-10-01
Diamond metal-oxide-semiconductor capacitors were prepared using atomic layer deposition at 250 °C of Al2O3 on oxygen-terminated boron doped (001) diamond. Their electrical properties were investigated in terms of capacitance and current versus voltage measurements. Performing X-ray photoelectron spectroscopy based on the measured core level energies and valence band maxima, the interfacial energy band diagram configuration of the Al2O3/O-diamond is established. The band diagram alignment is concluded to be of type I with valence band offset Δ E v of 1.34 ± 0.2 eV and conduction band offset Δ E c of 0.56 ± 0.2 eV considering an Al2O3 energy band gap of 7.4 eV. The agreement with electrical measurement and the ability to perform a MOS transistor are discussed.
Electronic ground state conformers of β-carotene and their role in ultrafast spectroscopy
NASA Astrophysics Data System (ADS)
Lukeš, Vladimír; Christensson, Niklas; Milota, Franz; Kauffmann, Harald F.; Hauer, Jürgen
2011-04-01
We present a study of ground state conformations of all-trans β-carotene using Density Functional Theory (DFT). To reproduce the carotenoid spectrum, the DFT approach was combined with the Multi-Reference Configuration Interaction. Our results show that the global minimum corresponds to an asymmetric structure where the β-ionone rings are twisted with respect to the polyene chain. The next higher-lying conformer is more s-cis symmetric and is populated at room temperature (30%). We discuss the relation of these conformers to S∗ and show that our model readily explains the temperature dependence and the narrowing of the ground state bleach at long population times.
Meron ground state of Rashba spin-orbit-coupled dipolar bosons.
Wilson, Ryan M; Anderson, Brandon M; Clark, Charles W
2013-11-01
We study the effects of dipolar interactions on a Bose-Einstein condensate with synthetically generated Rashba spin-orbit coupling. The dipolar interaction we consider includes terms that couple spin and orbital angular momentum in a way perfectly congruent with the single-particle Rashba coupling. We show that this internal spin-orbit coupling plays a crucial role in the rich ground-state phase diagram of the trapped condensate. In particular, we predict the emergence of a thermodynamically stable ground state with a meron spin configuration.
Investigation of the ground state of the anisotropic extended Hubbard chain at weak coupling
NASA Astrophysics Data System (ADS)
Ding, Hanqin; Zhang, Jun
2016-09-01
We study a one-dimensional anisotropic extended Hubbard model, where the inter-site density (V) and exchange (J) interactions are spin-dependent. Use of bosonization and renormalization helps investigate phase diagram. At half filling, the ground state characterizes insulating phases. The spin-dependent repulsion leads to a bond-spin-density-wave (BSDW) phase. The antiferromagnetic exchange enhances the bond-order-wave (BOW) phase while weakens the charge-density-wave (CDW) phase. When J > 4 V, the BSDW and CDW phases disappear. Away from half filling, the ground state exhibits superconducting behavior. The anisotropic interactions have an important effect on the phase structures.
Optical pumping of metastable NH radicals into the paramagnetic ground state
Meerakker, Sebastiaan Y.T. van de; Mosk, Allard P.; Jongma, Rienk T.; Sartakov, Boris G.; Meijer, Gerard
2003-09-01
We here report on the optical pumping of both {sup 14}NH and {sup 15}NH radicals from the metastable a {sup 1}{delta} state into the X {sup 3}{sigma}{sup -} ground state in a molecular beam experiment. By inducing the hitherto unobserved spin-forbidden A {sup 3}{pi} <- a {sup 1}{delta} transition, followed by spontaneous emission to the X {sup 3}{sigma}{sup -} state, a unidirectional pathway for population transfer from the metastable state into the electronic ground state is obtained. The optical pumping scheme demonstrated here opens up the possibility to accumulate NH radicals in a magnetic or optical trap.
Ground state mass of 81Kr and the solar neutrino problem
NASA Astrophysics Data System (ADS)
Kouzes, R. T.; Lowry, M. M.; Bennett, C. L.
1982-02-01
The 81Br(3He,t)81Kr, reaction has been used to determine an improved value for the ground state mass of 81Kr. A comparison is made with 51V(3He,t)51Cr and the implications for calibration of the proposed bromine solar neutrino detector are presented. NUCLEAR REACTIONS 81Br(3He,t)81Kr, 51V(3He,t)51Cr, 87Rb(3He,t)87Sr, 85Rb(3He,t)85Sr, E(3He)=24.7 MeV; Q values measured, ground state 81Kr mass inferred.
Dimerized ground state in the one-dimensional spin-1 boson Hubbard model
Apaja, Vesa; Syljuaasen, Olav F.
2006-09-15
We have investigated the one-dimensional spin-1 boson Hubbard model with antiferromagnetic interactions using quantum Monte Carlo methods. We obtain the shapes of the two lowest Mott lobes and show that the ground state within the lowest Mott lobe is dimerized. The results presented here are relevant for optically trapped antiferromagnetic spin-1 bosons. An experimental signature of the dimerized ground state is modulated Bragg peaks in the noise distribution of the atomic cloud obtained after switching off the trap. These Bragg peaks are located at wave vectors corresponding to half-integer multiples of the reciprocal wave vector of the optical lattice.
STABILITY IN BCC TRANSITION METALS: MADELUNG AND BAND-ENERGY EFFECTS DUE TO ALLOYING
Landa, A; Soderlind, P; Ruban, A; Peil, O; Vitos, L
2009-08-28
The phase stability of the bcc Group VB (V, Nb, and Ta) transition metals is explored by first-principles electronic-structure calculations. Alloying with a small amount of a neighboring metal can either stabilize or destabilize the bcc phase. This counterintuitive behavior is explained by competing mechanisms that dominate depending on particular dopand. We show that band-structure effects dictate stability when a particular Group VB metal is alloyed with its nearest neighbors within the same d-transition series. In this case, the neighbor with less (to the left) and more (to the right) d electrons, destabilize and stabilize bcc, respectively. When alloying with neighbors of different d-transition series, electrostatic Madelung energy dominates over the band energy and always stabilizes the bcc phase.
Vibrational effects on surface energies and band gaps in hexagonal and cubic ice
NASA Astrophysics Data System (ADS)
Engel, Edgar A.; Monserrat, Bartomeu; Needs, Richard J.
2016-07-01
Surface energies of hexagonal and cubic water ice are calculated using first-principles quantum mechanical methods, including an accurate description of anharmonic nuclear vibrations. We consider two proton-orderings of the hexagonal and cubic ice basal surfaces and three proton-orderings of hexagonal ice prism surfaces, finding that vibrations reduce the surface energies by more than 10%. We compare our vibrational densities of states to recent sum frequency generation absorption measurements and identify surface proton-orderings of experimental ice samples and the origins of characteristic absorption peaks. We also calculate zero point quantum vibrational corrections to the surface electronic band gaps, which range from -1.2 eV for the cubic ice basal surface up to -1.4 eV for the hexagonal ice prism surface. The vibrational corrections to the surface band gaps are up to 12% smaller than for bulk ice.
Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle
NASA Technical Reports Server (NTRS)
Elkadi, Asmaa; Decrossas, Emmanuel; El-Ghazaly, Samir
2013-01-01
The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of electron density for na individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closet neighbors reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%.
Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle
NASA Technical Reports Server (NTRS)
Elkadi, Asmaa; Decrossas, Emmanuel; El-Ghazaly, Samir
2013-01-01
The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of the electron density for an individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closest neighbours reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%.
Kolomeisky, Eugene B.; Kalas, Ryan M.; Straley, Joseph P.
2004-06-01
We analyze the ground-state properties of an artificial atom made out of repulsive bosons attracted to a center for the case that all the interactions are short ranged. Such bosonic atoms could be created by optically trapping ultracold particles of alkali-metal vapors; we present the theory describing how their properties depend on experimentally adjustable strength of 'nuclear' attraction and interparticle repulsion. The binding ability of the short-range potential increases with space dimensionality, only a limited number of particles can be bound in one dimension, while in two and three dimensions the number of bound bosons can be chosen at will. Particularly in three dimensions we find an unusual effect of enhanced resonant binding: for not very strong interparticle repulsion the equilibrium number of bosons bound to a nuclear potential having a sufficiently shallow single-particle state increases without bound as the nuclear potential becomes less attractive. As a consequence of the competing nuclear attraction enhanced by the Bose statistics and interparticle repulsions, the dependence of the ground-state energy of the atom on the number of particles has a minimum whose position is experimentally tunable. This implies a staircase dependence of the equilibrium number of bound bosons on external parameters which may be used to create a single-atom pipette--an arrangement which allows the transport of atoms into and out of a reservoir, one at a time.
NASA Astrophysics Data System (ADS)
Choi, Jinwoo; Chang, Eonho; Anstine, Dylan M.; Chakraborty, Himadri
2016-05-01
We study the ground state properties of C60 and C240 molecules in a spherical frame of local density approximation (LDA). Within this mean-field theory, two different approximations to the exchange-correlation (xc) functional are used: (i) The Gunnerson-Lundqvist parametrization augmented by a treatment to correct for the electron self-interaction and (ii) the van Leeuwen and Baerends (LB94) model potential that inclusively restores electron's asymptotic properties. Results show differences in the ground-state potential, level energies and electron densities between the two xc choices. We then use the ground structure to find the excited and ionized states of the systems and calculate dipole single-photoionization cross sections in a time-dependent LDA method that incorporates linear-response dynamical correlations. Comparative effects of the choices of xc on collective plasmon and single-excitation Auger resonances as well as on geometry driven cavity oscillations are found significant. The work is supported by the NSF, USA.
Precision measurements of proton emission from the ground states of {sup 156}Ta and {sup 160}Re
Darby, I. G.; Page, R. D.; Joss, D. T.; Bianco, L.; Grahn, T.; Judson, D. S.; Simpson, J.; Eeckhaudt, S.; Greenlees, P. T.; Jones, P. M.; Julin, R.; Juutinen, S.; Ketelhut, S.; Leino, M.; Leppaenen, A.-P.; Nyman, M.; Rahkila, P.; Saren, J.; Scholey, C.; Steer, A. N.
2011-06-15
The decays of the {pi}d{sub 3/2} ground states of {sup 156}Ta and {sup 160}Re have been studied in detail using the GREAT spectrometer. More than 7000 {sup 160}Re nuclei were produced in reactions of 290- and 300-MeV {sup 58}Ni ions with an isotopically enriched {sup 106}Cd target and separated in flight using the RITU separator. The proton and {alpha} decays of the {pi}d{sub 3/2} level were confirmed and the half-life and branching ratios of this state were determined with improved precision to be t{sub 1/2}=611{+-}7 {mu}s and b{sub p}=89{+-}1% and b{sub {alpha}=}11{+-}1%, respectively. The {alpha}-decay branch populated the ground state of {sup 156}Ta, allowing improved values for the proton-decay energy and half-life to be obtained (E{sub p}=1011{+-}5 keV; t{sub 1/2}=106{+-}4 ms). The {beta} decay of this level was identified for the first time and a branching ratio of b{sub {beta}=}29{+-}3% was deduced. The spectroscopic factors deduced from these measurements are compared with predictions.
Exact many-body ground states of a spin-1 Bose gas in Tonks-Girardeau limit
NASA Astrophysics Data System (ADS)
Jen, Hsiang-Hua; Yip, Sungkit
2016-05-01
We investigate the many-body ground states of a one-dimensional spin-1 Bose gas in Tonks-Girardeau (TG) limit. It is known that in TG gas limit of scalar bosons, the system becomes fermionized that bosons do not penetrate each other, and their wavefunctions take the form of noninteracting fermions. For a spin-1 Bose gas with an infinite atom-atom interaction in a harmonic trap, we construct the many-body ground states from the ones of a noninteracting Fermi gas along with the spin degrees of freedom. With zero magnetic field in the sector of Sz = 0 and in the regime of spin-incoherent Luttinger liquid where we assume negligible | a2 -a0 | , the interaction energy becomes spin-independent, and the many-body wavefunctions of a spin-1 Bose gas is also SU(3) invariant. The many-body wavefunction can be derived by calculating the weightings of spin functions using the conjugacy class G of SN symmetric group for the number of atoms N. We then study the first-order correlation function of the density matrix, from which we extract its momentum distribution. Finite-temperature calculation of the wavefunction by including orbital excitations is also investigated to compare with the case of spinless bosons. Ministry of Science and Technology, Taiwan, under Grant Number MOST-101-2112-M-001-021-MY3.
Brauner, Tomas
2008-12-15
We investigate spin-one color superconductivity of a single quark flavor using the Ginzburg-Landau theory. First we examine the classic analysis of Bailin and Love and show that by restricting to the so-called inert states, it misses the true ground state in a part of the phase diagram. This suggests the use of the more general, noninert states, in particular, within three-flavor quark matter where the color neutrality constraint imposes stress on the spin-one pairing and may disfavor the symmetric color-spin-locked state. In the second part of the paper we show that, in analogy to some ferromagnetic materials, lack of space-inversion symmetry leads to a new term in the Ginzburg-Landau functional, which favors a spatially nonuniform long-range ordering with a spiral structure. In color superconductors, this new parity-violating term is a tiny effect of weak-interaction physics. The modified phase diagram is determined and the corresponding ground states for all the phases constructed. At the end, we estimate the coefficient of the new term in the free energy functional, and discuss its relevance for the phenomenology of dense quark matter.
Bechlars, Bettina; D'Alessandro, Deanna M; Jenkins, David M; Iavarone, Anthony T; Glover, Starla D; Kubiak, Clifford P; Long, Jeffrey R
2010-05-01
The field of molecular magnetism has grown tremendously since the discovery of single-molecule magnets, but it remains centred around the superexchange mechanism. The possibility of instead using a double-exchange mechanism (based on electron delocalization rather than Heisenberg exchange through a non-magnetic bridge) presents a tantalizing prospect for synthesizing molecules with high-spin ground states that are well isolated in energy. We now demonstrate that magnetic double exchange can be sustained by simple imidazolate bridging ligands, known to be well suited for the construction of coordination clusters and solids. A series of mixed-valence molecules of the type [(PY5Me(2))V(II)(micro-L(br)) V(III)(PY5Me(2))](4+) were synthesized and their electron delocalization probed through cyclic voltammetry and spectroelectrochemistry. Magnetic susceptibility data reveal a well-isolated S = 5/2 ground state arising from double exchange for [(PY5Me(2))(2)V(2)(micro-5,6-dimethylbenzimidazolate)](4+). Combined modelling of the magnetic data and spectral analysis leads to an estimate of the double-exchange parameter of B = 220 cm(-1) when vibronic coupling is taken into account.
Augustine Band of Cahuilla Indians Energy Conservation and Options Analysis - Final Report
Paul Turner
2008-07-11
The Augustine Band of Cahuilla Indians was awarded a grant through the Department of Energy First Steps program in June of 2006. The primary purpose of the grant was to enable the Tribe to develop energy conservation policies and a strategy for alternative energy resource development. All of the work contemplated by the grant agreement has been completed and the Tribe has begun implementing the resource development strategy through the construction of a 1.0 MW grid-connected photovoltaic system designed to offset a portion of the energy demand generated by current and projected land uses on the Tribe’s Reservation. Implementation of proposed energy conservation policies will proceed more deliberately as the Tribe acquires economic development experience sufficient to evaluate more systematically the interrelationships between conservation and its economic development goals.
A model describing the pressure dependence of the band gap energy for the group III-V semiconductors
NASA Astrophysics Data System (ADS)
Zhao, Chuan-Zhen; Wei, Tong; Sun, Xiao-Dong; Wang, Sha-Sha; Lu, Ke-Qing
2016-08-01
A model describing the pressure dependence of the band gap energy for the group III-V semiconductors has been developed. It is found that the model describes the pressure dependence of the band gap energy very well. It is also found that, although the pressure dependence of the band gap energy for both the conventional III-V semiconductors and the dilute nitride alloys can be described well by the model in this work, the physical mechanisms for them are different. In addition, the influence of the nonlinear compression of the lattice on the band gap energy is smaller than that of the coupling interaction between the N level and the conduction band minimum of the host material.
Vanishing Electronic Energy Loss of Very Slow Light Ions in Insulators with Large Band Gaps
Markin, S. N.; Primetzhofer, D.; Bauer, P.
2009-09-11
Electronic energy loss of light ions in nanometer films of materials with large band gaps has been studied for very low velocities. For LiF, a threshold velocity is observed at 0.1 a.u. (250 eV/u), below which the ions move without transferring energy to the electronic system. For KCl, a lower (extrapolated) threshold velocity is found, identical for H and He ions. For SiO{sub 2}, no clear velocity threshold is observed for He particles. For protons and deuterons, electronic stopping is found to perfectly fulfill velocity scaling, as expected for binary ion-electron interaction.
The energy-band alignment at molybdenum disulphide and high-k dielectrics interfaces
Tao, Junguang; Chai, J. W.; Zhang, Z.; Pan, J. S.; Wang, S. J.
2014-06-09
Energy-band alignments for molybdenum disulphide (MoS{sub 2}) films on high-k dielectric oxides have been studied using photoemission spectroscopy. The valence band offset (VBO) at monolayer MoS{sub 2}/Al{sub 2}O{sub 3} (ZrO{sub 2}) interface was measured to be 3.31 eV (2.76 eV), while the conduction-band offset (CBO) was 3.56 eV (1.22 eV). For bulk MoS{sub 2}/Al{sub 2}O{sub 3} interface, both VBO and CBO increase by ∼0.3 eV, due to the upwards shift of Mo 4d{sub z{sup 2}} band. The symmetric change of VBO and CBO implies Fermi level pinning by interfacial states. Our finding ensures the practical application of both p-type and n-type MoS{sub 2} based complementary metal-oxide semiconductor and other transistor devices using Al{sub 2}O{sub 3} and ZrO{sub 2} as gate materials.
NASA Astrophysics Data System (ADS)
Colpitts, C. A.; Cattell, C. A.; Kozyra, J. U.; Thomsen, M. F.; Lavraud, B.
2016-07-01
Energy-banded ions from tens to ten thousands of eV are observed in the low-latitude auroral and subauroral zones during every large (minimum Dst < -150 nT) geomagnetic storm encountered by the FAST satellite. The banded ions persist for many FAST orbits, lasting up to 12 h, in both the northern and southern hemispheres. The energy-banded ions often have more than six distinct bands, and the O+, He+, and H+ bands are often observed at the same energies. The bands are extensive in latitude (~50-75° on the dayside, often extending to 45°) and magnetic local time, covering all magnetic local time over the data set of storms. The distributions are peaked in the perpendicular direction at the altitudes of the FAST satellite (~350-4175 km), although in some cases the precipitating component dominates for the lowest energy bands. At the same time, for some of the events studied in detail, long-lasting intervals of field-aligned energy dispersed ions from ~100 eV to 40 keV are seen in Los Alamos National Laboratory geosynchronous observations, primarily on the dayside and after magnetosheath encounters (i.e., highly compressed magnetosphere). We present both case and statistical studies of the banded ions. These bands are a new phenomenon associated with all large storms, which are distinctly different from other banded populations, and are not readily interpreted using previous models for particle sources, transport, and loss. The energy-banded ions are an energetically important component of the inner magnetosphere during the most intense magnetic storms.
The role of solvents in framework dimensionality and their effect on band gap energy.
Asha, K S; Kavyasree, P R; George, Anu; Mandal, Sukhendu
2015-01-21
The crystal growth rate and morphology can be modulated by tuning the ratio of the solvent in mixed solvents during synthesis. We present here a solvothermal method to synthesize a Cd-FDC based metal-organic framework with different morphologies by tuning the ratio of water in the DMF-water mixed solvent system without adding any other additives. With the increasing water volume ratio a series of crystals with different morphologies were synthesized. Among these we have isolated two single crystal structures, [Cd3(FDC)3(DMF)4(H2O)], and [DMA]2[Cd3(FDC)4]·2H2O, . Compound was synthesized from DMF with small amounts of water while was formed from 25 vol% of water in the DMF-water mixed solvent. Compound contains trimer clusters as building units, which are linked by the furan dicarboxylate ligand to form a two-dimensional structure. Compound also contains trimer clusters which are linked to each other to form a one-dimensional chain with the Cd-O-Cd linkage. This one-dimensional chain in turn is connected by the furan dicarboxylate ligand to form a three-dimensional structure. All these structures are characterized by SEM, XRD, TGA and IR. We have measured the band gap energy and measurements show that the values are decreasing from to . The lower band gap energy of may be due to the presence of infinite Cd-O-Cd linkages which split the states of the conduction band and reduces the band gap energy.
An, Hui-Ying; Ma, Chensheng; Nganga, Jameil L; Zhu, Yue; Dore, Timothy M; Phillips, David Lee
2009-03-26
The 8-bromo-7-hydroxyquinolinyl group (BHQ) is a derivative of 7-hydroxyquinoline (7-HQ) and BHQ molecules coexisting as different forms in aqueous solution. Absorption and resonance Raman spectroscopic methods were used to examine 8-bromo-7-hydroxyquinoline protected acetate (BHQ-OAc) in acetonitrile (MeCN), H(2)O/MeCN (60:40, v/v, pH 6 approximately 7), and NaOH-H(2)O/MeCN (60:40, v/v, pH 11 approximately 12) to obtain a better characterization of the forms of the ground-state species of BHQ-OAc in aqueous solutions and to examine their properties. The absorption spectra of BHQ-OAc in water show no absorption bands of the tautomeric species unlike the strong band at about 400 nm observed for the tautomeric form in 7-HQ aqueous solution. The resonance Raman spectra in conjunction with Raman spectra predicted from density functional theory (DFT) calculations reveal the observation of a double Raman band system characteristic of the neutral form (the nominal C=C ring stretching, C-N stretching, and O-H bending modes at 1564 and 1607 cm(-1)) and a single Raman band diagnostic of the enol-deprotonated anionic form (the nominal C=C ring, C-N, and C-O(-) stretching modes in the 1593 cm(-1) region). These results suggest that the neutral form of BHQ-OAc is the major species in neutral aqueous solution. There is a modest increase in the amount of the anionic form and a big decrease in the amount of the tautomeric form of the molecules for BHQ-OAc compared to 7-HQ in neutral aqueous solution. The presence of the 8-bromo group and/or competitive hydrogen bonding that hinder the formation and transfer process of a BHQ-OAc-water cyclic complex may be responsible for this large substituent effect. PMID:19296708