Search results for "Atomic orbital"
showing 10 items of 233 documents
Comparative Theoretical Analysis of BN Nanotubes Doped with Al, P, Ga, As, In, and Sb
2013
SUMMARY AND CONCLUDING REMARKS We have performed large-scale first-principles calculations ofthe electronic structure of (5,5) boron nitride nanotubescontaining the following substitutional impurity atoms: Al, P,Ga, As, In, and Sb. Calculations have been performed using thetwo methods: (i) linear combination of atomic orbitals(LCAO) with the atomic-centered Gaussian-type functions asa basis set and (ii) linearized augmented cylindrical wave(LACW) accompanied with the local density functional andmuffin-tin approximations for the electronic potential. In arelatively good qualitative agreement, both methods predict lowformation energies and, thus, relative stability of point defectsthat are assoc…
Ab initio calculations of structural, electronic and vibrational properties of BaTiO3 and SrTiO3 perovskite crystals with oxygen vacancies
2020
The first-principles (ab initio) computations of the structural, electronic, and phonon properties have been performed for cubic and low-temperature tetragonal phases of BaTiO3 and SrTiO3 perovskite crystals, both stoichiometric and non-stoichiometric (with neutral oxygen vacancies). Calculations were performed with the CRYSTAL17 computer code within the linear combination of atomic orbitals approximation, using the B1WC advanced hybrid exchange-correlation functional of the density-functional-theory (DFT) and the periodic supercell approach. Various possible spin states of the defective systems were considered by means of unrestricted (open shell) DFT calculations. It was demonstrated that…
Communication: multireference equation of motion coupled cluster: a transform and diagonalize approach to electronic structure.
2014
The novel multireference equation-of-motion coupled-cluster (MREOM-CC) approaches provide versatile and accurate access to a large number of electronic states. The methods proceed by a sequence of many-body similarity transformations and a subsequent diagonalization of the transformed Hamiltonian over a compact subspace. The transformed Hamiltonian is a connected entity and preserves spin- and spatial symmetry properties of the original Hamiltonian, but is no longer Hermitean. The final diagonalization spaces are defined in terms of a complete active space (CAS) and limited excitations (1h, 1p, 2h, …) out of the CAS. The methods are invariant to rotations of orbitals within their respective…
Multi-scale multireference configuration interaction calculations for large systems using localized orbitals: Partition in zones
2012
A new multireference configuration interaction method using localised orbitals is proposed, in which a molecular system is divided into regions of unequal importance. The advantage of dealing with local orbitals, i.e., the possibility to neglect long range interaction is enhanced. Indeed, while in the zone of the molecule where the important phenomena occur, the interaction cut off may be as small as necessary to get relevant results, in the most part of the system it can be taken rather large, so that results of good quality may be obtained at a lower cost. The method is tested on several systems. In one of them, the definition of the various regions is not based on topological considerati…
Calculation of electronic g-tensors using coupled cluster theory.
2009
A scheme for the calculation of the electronic g-tensor at the coupled cluster (CC) level is presented. The reported implementation employs an effective one-electron spin-orbit operator, allows the inclusion of arbitrary excitations in the cluster operator, and offers various options concerning the treatment of orbital relaxation and choice of reference determinants. In addition, the use of gauge-including atomic orbitals (GIAOs) is possible to overcome the gauge origin problem. Benchmark calculations for the NH ((3)Sigma(-)) radical reveal the importance of electron correlation effects for the accurate prediction of the g-shift as well as the slow basis set convergence of such calculations…
Electron Spin Resonance study of charge trapping in α-ZnMoO4 single crystal scintillator
2015
The origin and properties of electron and hole traps simultaneously appearing in a-ZnMoO4 scintillator after X-ray irradiation at low temperatures (T < 35 K) were studied by Electron Spin Resonance (ESR). ESR spectrum of the electron type trap shows pronounced superhyperfine structure due to the interaction of electron spin with nuclear magnetic moments of 95,97Mo and 67Zn lattice nuclei. Considering the nearly tetragonal symmetry of the center this allows us to identify the electron trap as an electron self-trapped at the (Mo(1)O4) 2 complex. Nearly 60% reduction of the spin–orbit coupling at the Mo(1) ion is caused by the overlap of the Mo and ligand oxygen orbitals indicating an essentia…
Ab initio calculations of pure and Co+2-doped MgF2 crystals
2020
This research was partly supported by the Kazakhstan Science Project № AP05134367«Synthesis of nanocrystals in track templates of SiO2/Si for sensory, nano- and optoelectronic applications», as well as by Latvian Research Council project lzp-2018/1-0214. Calculations were performed on Super Cluster (LASC) in the Institute of Solid State Physics (ISSP) of the University of Latvia. Authors are indebted to S. Piskunov for stimulating discussions.
External pressure and composition effects on the atomic and electronic structure of SnWO4
2015
The atomic and electronic structure of tin tungstates, α-SnWO4, α-Sn1.03W0.99O4 and β-SnWO4 ,w as studied by the W L3-edge X-ray absorption spectroscopy and first-principles linear combination of atomic orbital (LCAO) calculations based on the hybrid exchange-correlation density functional (DFT)/ Hartree–Fock (HF) scheme. It was found that the crystal structure of both α-phases is built up of strongly distorted WO6 octahedra, whereas that of β-SnWO4 is composed of nearly regular WO4 tetrahedra. In addition, there are distorted SnO6 octahedra in both α- and β-phases. The metal–oxygen octahedra distortion is explained by the second-order Jahn–Teller effect. The influence of pressure on the st…
Pseudo-Jahn–Teller Origin of the Metastable States in Sodium Nitroprusside
2003
Abstract A new model for the photochromic effect in sodium nitroprusside Na 2 [Fe(CN) 5 (NO)]·2H 2 O based on the concept of the pseudo-Jahn–Teller effect is proposed. The model takes into account the electron transfer from the Fe 2+ ion to the π ∗ orbitals of the NO-ligand as well as the vibronic mixing of three electronic states of the Fe–NO fragment through the non-symmetric and full symmetric modes. The problem is solved within the adiabatic approximation. Under certain conditions, the lower sheet of the adiabatic potential is shown to possess three minima with the increasing energies that correspond to the N-bound, sideways bound, and O-bound NO group. The barriers between the minima a…
Cu–Cu interactions in the transparent p-type conductors: CuAlO2 and SrCu2O2
2003
Abstract Electronic structures of the p-type Transparent Conducting Oxides (TCO): CuAlO2 and SrCu2O2 are calculated using the Tight Binding Linearized Muffin Tin Orbital within the Atomic Sphere Approximation method (TB-LMTO-ASA). The band structures indicate two gaps for CuAlO2 (an indirect one with ΔE≈0.45 eV and a direct one with ΔE≈1.25 eV) and one direct gap for SrCu2O2 (with ΔE≈2 eV). In both oxides the Cu states are dominant at the top of the valence band, close to the Fermi level and the existence of weak Cu–Cu bonding interactions is revealed through the Integrated Crystal Orbital Hamiltonian Population (ICOHP). The presence of such interactions suggests that for the hole doped oxi…