Search results for "atomic physics"
showing 10 items of 5530 documents
Ab initio calculations of the atomic and electronic structure of BaZrO3 (111) surfaces
2013
Abstract The paper presents and discusses the results of calculations of surface relaxations and energetics for the polar (111) surface of BaZrO 3 using a hybrid B3LYP description of exchange and correlation. On the (111) surface, both Zr- and BaO 3 -terminations were analyzed. For both Zr and BaO 3 -terminated BaZrO 3 (111) surface upper layer atoms, with the sole exception of BaO 3 -terminated surface Ba atoms, relax inwards. The Zr-terminated BaZrO 3 (111) surface second layer Ba atoms exhibit the strongest relaxation between all Zr and BaO 3 -terminated BaZrO 3 (111) surface atoms. The calculated surface relaxation energy for Zr-terminated BaZrO 3 (111) surface is almost fifteen times l…
Comparative analysis of the electronic structures of mono- and bi-atomic chains of IV, III–V and II–VI group elements calculated using the DFT LCAO a…
2015
Using the first principle non-relativistic linear combination of atomic orbitals (LCAO) and relativistic linearized augmented cylindrical wave (LACW) methods, the band structure of the covalent and partially ionic ANB8−N single atom width chain is calculated. Both the LCAO and LACW methods show that the chains of C, Si, Ge, Sn, and Pb are metallic. However, there is a great difference between the relativistic and non-relativistic band structures. The π bands crossing the Fermi level are orbitally doubly degenerate in the non-relativistic model. The relativistic LACW calculations demonstrate that the spin and orbital motion of electrons are coupled, thereby splitting the π bands. The spin–or…
First principles calculations of SrZrO3 bulk and ZrO2-terminated (001) surface F centers
2016
Abstract Using a supercell model and B3PW hybrid exchange-correlation functional in the framework of the density functional theory (DFT), as it is implemented in the CRYSTAL computer code, we performed ab initio calculations for the F -center located in the SrZrO 3 bulk and on the ZrO 2 -terminated (001) surface. According to the results of performed relaxation of atoms around the defect, two nearest Zr and four Sr atoms are repulsed, but all oxygen atoms are attracted towards both, the bulk and (001) surface F -center. The displacement magnitudes of atoms surrounding the bulk F -center are smaller than around the (001) surface F -center. The B3PW calculated SrZrO 3 bulk optical band gap (5…
A model for the γN → ππN reaction
1995
We have studied the γN→ππN reaction using a model which includes N, Δ(1232), N*(1440) and N*(1520) intermediate baryonic states and the ρ-meson as intermediate ππ resonance. The model reproduces fairly well experimental cross sections below E γ = 800 MeV and invariant-mass distributions even at higher energies. One of the interesting findings of the study is that the γ N →N*(1520) → Δπ process is very important and interferes strongly with the dominant Δ-Kroll-Ruderman term to produce the experimental peak of the cross section.
Unitary coupled channel analysis of theΛ(1520)resonance
2006
We study the � (1520) resonance in a coupled-channel approach involving the π� (1385) ,K� (1530), ¯ KN, and π� channels. Implementing unitarity in coupled channels, we make an analysis of the relative importance of the different mechanisms that contribute to the dynamical structure of this resonance. From experimental information on some partial wave amplitudes and constraints imposed by unitarity, we get a comprehensive description of the amplitudes and hence the couplings to the different channels. We test these amplitudes in different reactions like K − p → �π π, γp → K + K − p, γp → K + π 0 π 0 � ,a ndπ − p → K 0 K − p and find a fair
Λ(1520)andΣ(1385)in the nuclear medium
2006
Recent studies of the {lambda}(1520) resonance within chiral unitary theory with coupled channels find the resonance as a dynamically generated state from the interaction of the decuplet of baryons and the octet of mesons, essentially a quasibound state of {pi}{sigma}{sup *}(1385) in this case, although the coupling of the {lambda}(1520) to the KN and {pi}{sigma} makes this picture only approximate. The {pi}{sigma}{sup *}(1385) decay channel of the {lambda}(1520) is forbidden in free space for the nominal mass of the {sigma}{sup *}(1385), but the coupling of the {pi} to ph components in the nuclear medium opens new decay channels of the {lambda}(1520) in the nucleus and produces a much larg…
Improved comparison of bar P and P charge-to-mass ratios
1995
The measured ratio of charge-to-mass ratios for the antiproton and proton is 1.000 000 001 5 ± 0.000 000 001 1. This 1 part in 109 comparison (1 ppb) is possible because a single or p is now directly observed while trapped in an open access Penning trap. The comparison is the most accurate mass spectrometry of particles with opposite charge and is the most sensitive test of CPT invariance for a baryon system. It is 40 times more accurate than our earlier comparison with many trapped antiprotons and protons, and is more than 45 000 times more accurate than earlier comparisons made with other techniques.
VECTOR-BARYON DYNAMICS IN γN → K0Σ REACTIONS
2014
A coupled channel model for the interaction of vector mesons with baryons is employed in the study of the γp → K0Σ+ reaction around the K*Λ and K*Σ thresholds, where the recent CBELSA/TAPS cross section shows a sudden drop and the differential cross section experiences a transition from a forward-peaked distribution to a flat one. A delicate interference between amplitudes having K*Λ and K*Σ intermediate states is found. The sharp downfall is dictated by the presence of a N* resonance produced by our model, a feature that we have employed to infer its properties. Predictions for the complementary γn → K0Σ0 reaction are also given.
The accuracy of molecular dipole moments in standard electronic structure calculations
2000
Abstract A systematic investigation has been carried out of the accuracy of calculated molecular equilibrium dipole moments of 11 polar closed-shell molecules, using the HF, MP2, CCSD and CCSD(T) models and correlation-consistent basis sets. Augmented basis sets are important for improving the basis-set convergence, but the quality of the results depends more on the correlation treatment than on the cardinal number of the basis set. Augmented triple-zeta basis sets are sufficient for most calculations. The mean absolute error of the HF calculations is 0.16 D, which is reduced at the MP2 and CCSD levels to 0.048 and 0.025 D, respectively. The CCSD(T) errors are small – typically
The electronic spectrum of pyrrole
1999
The electronic spectrum of pyrrole has been investigated by performing calculations using a hierarchy of coupled-cluster models consisting of CCS, CC2, CCSD, and CC3. Basis-set effects have been investigated by carrying out calculations using correlation-consistent basis sets augmented with functions especially designed for the description of Rydberg states. Oscillator strengths, excited state dipole moments, and second moments of the electronic charge distributions have been used to characterize the electronic transitions and final states. Structures and vibrational frequencies have been calculated for a few selected states, and the importance of distinguishing between vertical and adiabat…