The method for localizing orbitals on a set of predefined molecular fragments is introduced. Regional localized molecular orbitals (RLMO) are obtained through block diagonalization of the one-electron density matrix and further refinement of the resulting eigenvectors. The algorithm is fast and reliable, as is illustrated by a few examples. Potential applications range from conceptual insight into a chemical bonding to reduced scaling computational techniques. RLMOs are particularly well suited for fragmentation computational methods and for exploiting the locality of electronic correlation in post-HF methods.
The magnetoresistance, irreversibility fields, and critical current density were studied for a commercial 2G tape at the two relative orientations of magnetic field and superconductor plane. The critical temperatures of this tape of T c50 % = 91.5 K and T c0 = 90 K and the width of superconducting transition of T = 1.5 K were obtained. The widths of the transition from the normal to the superconducting state do not increase at the applied magnetic field up to 90 kOe and do not depend on the orientation of the magnetic field with respect to the tape plane. The irreversibility field values were obtained and successfully fitted as a function of temperature using the formula:The irreversibility fields show an anisotropy, and at the liquid nitrogen temperature, they reach H irr = 430 kOe and H irr = 106 kOe for the parallel and perpendicular directions, respectively. The anisotropy ratio amounts to γ = 4 at 77 K and is small in comparison with other high-temperature superconducting materials. The critical current density of this tape was found to be of the order of 10 6 A cm −2 at 77 K in the self-magnetic field.
The c-axis orientation YBa2Cu3O δ thin film was prepared directly on MgO substrate by the pulse laser deposition. The thickness of the film is 170 nm. The superconducting critical temperature is T c50% = 87.5 K and the width of superconducting transition is ∆T = 1.8 K. The temperature dependences of magnetoresistance were measured up to 90 kOe. The widths of the transition to the superconducting state versus applied magnetic field were derived and they were fitted using the formula: ∆T = CH m + ∆T0. The irreversibility fields as a function of temperature were obtained and fitted by the de Almeida and Thouless-like equation: Hirr = Hirr0(1−T /Tc0) n . The irreversibility field at the liquid nitrogen temperature was calculated and it is Hirr = 43.8 kOe when the applied magnetic field is parallel to the c-axis.
The paper reports on the temperature dependencies of the electrical resistivity and the a.c. magnetic susceptibility of the Tl 0.8 Bi 0.3 Sr 1.8 Ba 0.2 Ca 2 Cu 3 O x bulk superconductor measured in the area of the transition from the metallic to the superconducting state. From the resistivity data, the onset temperature T c,onset = 121.6 K, the critical temperature T c50% = 118.8 K, the zero resistance critical temperature obtained using E = 10 −6 V/cm criterion T c0 = 117.9 K, and the width of superconducting transition T = 1.6 K were derived. The thermal fluctuations were examined using the formulae for the conductance: σ = Kε −λ , and for the magnetic susceptibility:λ is the critical exponent, and K and C are constants. The critical exponents in the transition region from the normal to the superconducting state were determined and analyzed. The three-dimensional fluctuations were found to occur in the vicinity of the zero-resistance critical temperature.
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