0000000000266389
AUTHOR
H. Shi
showing 10 related works from this author
First-principles calculations on surface hydroxyl impurities in BaF2
2012
Abstract OH − impurities located near the (1 1 1) BaF 2 surface have been studied by using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW. Twenty surface OH − configurations were studied, and the hydroxyls located on the first surface layer are the energetically most favorable configurations. For the (1 1 1) BaF 2 surface atomic layers, the surface hydroxyls lead to a remarkable XY -translation and a dilating effect in the Z -direction, overcoming the surface shrinking effect in the perfect slab. Bond population analysis shows that the surface effect strengthens the covalency of surface OH − impurities. The studies on band structures and density of states (…
First principles studies of the self trapped hole and the fluorine adsorption on the SrF2(111) surface
2013
Abstract By using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW, the ground states of self trapped hole and adsorbed fluorine atom on the strontium fluoride (1 1 1) surface are investigated. The self trapped hole at an interstitial anion site is denoted by H-center. In both the H-center and fluorine adsorption cases, the strong relaxations due to the surface effects are observed. In the H-center case, the unpaired electron distributes almost equally over two H-center atoms. This equivalent distribution of the unpaired electron is totally different from that of the bulk H-center [J. Phys. Chem. A 114 (2010) 8444]. The other case with an adsorbed fluorine at…
First-principles simulations on the aggregation of F centers in BaF2: R centers
2011
Abstract F center (an electron trapped in the fluorine vacancy) and R center (a defect composed of three F centers) in BaF 2 crystal, have been studied by using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW. Our calculations show that the F -center transfer barrier is equal to 1.83 eV. During the F -center transfer, the trapped electron is more delocalized than that in the static F -center case, and the gap between defect leveland CB in the α-spin state decreases obviously. The association energy calculations on R centers indicate stable aggregations of isolated F centers. During F -center aggregation, a considerable covalency between two neighbor fluorine…
Ab initio calculations of the hydroxyl impurities in BaF2
2011
Abstract OH − impurities in BaF 2 crystal have been studied by using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW. Three different configurations of OH − impurities were investigated and the (1 1 1)-oriented OH − configuration is the most stable one. Our calculations show that OH − as an atomic group has a steady geometrical structure instead of electronic properties in different materials. The studies on band structures and density of states (DOS) of the OH − -impurity systems indicate that there are two defect levels induced by OH − impurities. The two superposed occupied OH − -bands located 1.95 eV above the valance bands (VB) at Γ point mainly consist…
First-principles simulations of H centers in CaF2
2014
Abstract H center, a hole trapped at an interstitial anion site, placed in the bulk and the (1 1 1) surface of calcium fluoride CaF2, has been studied by using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW. The H center orients the (1 1 1) direction for the bulk case and the (1 0 0) direction for the surface case, and the hole is mainly localized on the interstitial fluorine. The surface H center leads to a remarkable XY-translation of the surface atoms. Spin and hyperfine coupling calculations show a considerable interaction between the unpaired spin and the spin of neighboring nuclei, and the surface effect strengthens the spin polarization and hyperfine…
First-principles calculations of surfaceHcenters inBaF2
2010
H center, a hole trapped at an interstitial anion site, placed on the 111 surface of Barium fluoride BaF2 has been studied by using density functional theory DFT with hybrid exchange potentials, namely, DFT-B3PW. Two different configurations of surface H center are investigated carefully. Both surface H-center systems have strong relaxations because of the surface effect. In the configuration that the interstitial fluorine atom is within the surface, named case 1 in this paper, the unpaired electron is almost equally distributed onto the two atoms of the H center, which is quite different from the bulk H-center case. The other configuration with one of the F atoms of the H center located ab…
Ab initio calculations for the F-center transfer and R centers in SrF2
2013
We have simulated the F-center transfer and R center in SrF2 crystal by using density functional theory (DFT) with a hybrid B3PW description of exchange and correlation. Our calculations show that the F-center diffusion barrier is equal to 1.84 eV. During the F-center transfer, the trapped electron is more delocalized than that in the regular F-center case, and the gap between defect level and conduction bands (CB) in the a-spin state decreases. The formation energy calculations of R center show the trend of F centers to aggregate in SrF2. During the F-center aggregation, a considerable covalency forms between two neighboring fluorine vacancies with trapped electrons. Three incompletely pai…
GSC 07396-00759 = V4046 Sgr C[D]: A Wide-separation Companion to the Close T Tauri Binary System V4046 Sgr AB
2011
We explore the possibility that GSC 07396-00759 (spectral type M1e) is a widely separated (~2.82', or projected separation ~12,350 AU) companion to the "old" (age ~12 Myr) classical T Tauri binary system V4046 Sgr AB, as suggested by the proximity and similar space motions of the two systems. If the two systems are equidistant and coeval, then GSC 07396--00759, like V4046 Sgr AB, must be a spectroscopic binary with nearly equal-mass components, and V4046 Sgr must be at least ~8 Myr old. Analysis of a serendipitous Chandra X-ray gratings spectrum and light curve as well as XMM-Newton light curves and CCD spectra of GSC 07396-00759 obtained during long exposures targeting V4046 Sgr AB reveals…
Ab Initio Calculations of Hydroxyl Impurities in CaF2
2012
OH– in CaF2 crystal and the (111) surface have been studied by using density functional theory (DFT) with hybrid exchange potentials, namely, DFT-B3PW. Three bulk and 20 surface OH– configurations ...
Ab Initio Calculations of the Transfer and Aggregation of F Centers in CaF2
2012
The F center and R center in CaF2 crystals have been studied by using density functional theory (DFT) with a hybrid B3PW description of exchange and correlation. Our calculations show that the F-center diffusion barrier is equal to 1.67 eV. During the F-center transfer, the trapped electron is more delocalized than that in the regular F-center case, and the gap between defect level and CB in the α-spin state decreases. The surface F-center investigation shows the trend of F centers to locate near the surface. The association energy calculations of R centers indicate stable aggregations of isolated F centers. During the F-center aggregation, a considerable covalency forms between two neighbo…