Search results for "Interaction"
showing 10 items of 5710 documents
Analytic energy gradients in closed-shell coupled-cluster theory with spin-orbit coupling
2008
Gradients in closed-shell coupled-cluster (CC) theory with spin-orbit coupling included in the post Hartree-Fock treatment have been implemented at the CC singles and doubles (CCSD) level and at the CCSD level augmented by a perturbative treatment of triple excitations [CCSD(T)]. The additional computational effort required in analytic energy-gradient calculations is roughly the same as that for ground-state energy calculations in the case of CCSD, and it is about twice in the case of CCSD(T) calculations. The structures, harmonic frequencies, and dipole moments of some heavy-element compounds have been calculated using the present analytic energy-gradient techniques including spin-orbit co…
Dynamics of a two-state system through a real level crossing
2015
The dynamics of a two-state system whose energies undergo a real crossing at some instant of time is studied. At this instant, both the coupling and the detuning vanish simultaneously, which leads to an exact degeneracy of the eigenenergies of the system. It is found that the dynamics of the system is primarily determined by the manner in which the degeneracy occurs. This interesting behavior is reminiscent of a symmetry breaking process, since the totally symmetric situation occurring at the crossing is significantly altered by infinitesimal quantities, which remove the degeneracy, with very important dynamical implications from there on. A very simple analytical formula is derived, which …
Glass physics: still not transparent
1999
Glass is a commonplace word. One immediately thinks of windows or bottles and of properties like brittleness or transparency. However, for a glass blower another feature is more important: glass does not melt abruptly, as a crystal does, but gradually over a range of temperatures. This means that he or she can alter the temperature at which glass solidifies or becomes a liquid by changing the rate at which it is cooled or heated. This is in stark contrast to the behaviour observed when the crystalline form of a material is heated: it will always melt at the same temperature.
Mechanically Based Nonlocal Euler-Bernoulli Beam Model
2014
AbstractThis paper presents a nonlocal Euler-Bernoulli beam model. It is assumed that the equilibrium of a beam segment is attained because of the classical local stress resultants, along with long-range volume forces and moments exchanged by the beam segment with all the nonadjacent beam segments. Elastic long-range volume forces/moments are considered, built as linearly depending on the product of the volumes of the interacting beam segments and on generalized measures of their relative motion, based on the pure deformation modes of the beam. Attenuation functions governing the space decay of the nonlocal effects are introduced. The motion equations are derived in an integro-differential …
Exchange Interactions I: Mechanisms
1996
A most important phenomenon in molecular magnetism is the exchange interaction between magnetic centers. Its relevance as well as the terms and concepts required to its rationalization were stated long ago by physicists working in the quantum-mechanical theory of magnetism (Heisenberg, Dirac, van Vleck, Anderson, Zener, and many others). Depending on the extent of delocalization of the magnetic moments and on the metallic/non-metallic properties of the solid four kinds of exchange coupling were usually distinguished in the physical literature namely direct exchange, superexchange, indirect exchange and itinerant exchange [1]. The relations of these types of couplings are depicted in Figure …
PNO-CI and CEPA studies of electron correlation effects
1974
Ab initio calculations of the potential curves of low laying electronic states of OH are performed on the basis of a variational configuration interaction wavefunction (PNO-CI) and the coupled electron pair approximation (CEPA). The latter approach yields a ground state potential curve which deviates from the RKR curve by less than 200 cm−1 in the region from 0.7 to 1.6 A. Calculated ground state constants are as follows (experimental values in parentheses): r e = 0.972 (0.971) A, B e = 18.85 (18.87) cm−1, α e = 0.727 (0.714) cm−1, ω e = 3742 (3739) cm−1, ω e χ e = 85.3 (86.4) cm−1, μ0 = 1.686 (1.66) D, D e = 4.35 (4.63) eV,IP = 12.78 (13.36?) eV, El.Aff. = 1.51 (1.83) eV, v 00(2Π↔2Σ+) = 32…
Unmixing of binary alloys by a vacancy mechanism of diffusion: a computer simulation
1991
The initial stages of phase separation are studied for a model binary alloy (AB) with pairwise interactions e AA , e AB , e BB between nearest neighbors, assuming that there is no direct interchange of neighboring atoms possible, but only an indirect one mediated by vacancies (V) occurring in the system at a concentrationc v and which are strictly conserved, as are the concentrationsc A andc B of the two species.A-atoms may jump to vacant sites with jump rateГ A , B-atoms with jump rateГ B (in the absence of interactions). Particular attention is paid to the question to what extent nonuniform distribution of vacancies affects the unmixing kinetics. Our study focuses on the special caseГ A =…
Calculation of atomic spectra and transition amplitudes for superheavy element Db (Z=105)
2018
Atomic spectra and other properties of superheavy element dubnium (Db, $Z=105$) are calculated using recently developed method combining configuration interaction with perturbation theory [the CIPT method, V. A. Dzuba, J. C. Berengut, C. Harabati, and V. V. Flambaum, Phys. Rev. A 95, 012503 (2017)]. These include energy levels for low-lying states of Db and Db II, electric dipole transition amplitudes between the ground state and low-lying states of opposite parity, isotope shift for these transitions, and the ionization potential of Db. Similar calculations for Ta, which is a lighter analog of Db, are performed to control the accuracy of the calculations.
A precise measurement of the real part of the elastic scattering amplitude at the Sp̄pS
1993
Abstract A precise measurement of pp elastic scattering in the Coulomb-strong interaction interference region was performed at the CERN SppS Collider at a centre-of-mass energy of 541 GeV. The ratio of the real to the imaginary part of the forward elastic scattering amplitude was found to be ρ = 0.135 ± 0.015. The slope of the exponential fall off of the strong interaction part was also measured to be b = 15.5 ± 0.1 GeV −2 .
The coherent weak charge of matter
2017
We study the long-range force arising between two aggregates of ordinary matter due to a neutrino-pair exchange, in the limit of zero neutrino mass. Even if matter is neutral of electric charge, it is charged for this weak force. The interaction is described in terms of a coherent charge, which we call the weak flavor charge of aggregated matter. For each one of the interacting aggregates, this charge depends on the neutrino flavor as $Q_W^{\nu_e} = 2Z-N$, $Q_W^{\nu_\mu} = Q_W^{\nu_\tau} = -N$, where $Z$ is the number of protons and $N$ the number of neutrons. $Q_W^{\nu_e}$ depends explicitly on $Z$ because of the charged current contribution to $\nu_e e$ elastic scattering, while the $N$ t…