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Recently, we have proposed the adaptive local basis set for electronic structure calculations based on Kohn–Sham density functional theory in a pseudopotential framework. The adaptive local basis set is efficient and systematically improvable for total energy calculations. In this paper, we present the calculation of atomic forces, which can be used for a range of applications such as geometry optimization and molecular dynamics simulation. We demonstrate that, under mild assumptions, the computation of atomic forces can scale nearly linearly with the number of atoms in the system using the adaptive local basis set. We quantify the accuracy of the Hellmann–Feynman forces for a range of physical systems, benchmarked against converged planewave calculations, and find that the adaptive local basis set is efficient for both force and energy calculations, requiring at most a few tens of basis functions per atom to attain accuracies required in practice. Since the adaptive local basis set has implicit dependence on atomic positions, Pulay forces are in general nonzero. However, we find that the Pulay force is numerically small and systematically decreasing with increasing basis completeness, so that the Hellmann–Feynman force is sufficient for basis sizes of a few tens of basis functions per atom. We verify the accuracy of the computed forces in static calculations of quasi-1D and 3D disordered Si systems, vibration calculation of a quasi-1D Si system, and molecular dynamics calculations of H 2 and liquid Al–Si alloy systems, where we show systematic convergence to benchmark planewave results and results from the literature. [ABSTRACT FROM AUTHOR]

The title compounds are prepared by solid state reaction of stoichiometric mixtures of the elements (823-1323 K, 12-96 h). [ABSTRACT FROM AUTHOR]

Abstract: We report on the scintillation properties of undoped PbI2, and PbI2 doped with La, Cu, Ag, and Te. X-ray luminescence spectra were recorded at 7K and the time responses for 80ps pulses of X-rays were recorded from 14K to 150K. Samples were irregularly shaped crystal pieces that ranged from 300 to 1000μm in size. We found that at 14K the undoped samples had a fast emission at 520nm (0.18eV below the band edge) and a total light output of about 40,000photons/MeV. 10% of this light appears in the first ns, which is 5 times greater than LSO and 1.5 times greater than LaBr3:Ce. 50% of the light appears in the first 100ns. The luminosity decreased dramatically as the temperature was increased above 40K, consistent with a non-radiative path that has an activation energy of 3.8meV. Doping with the donor La3+ only slightly changed these scintillation properties. Doping with the donor La3+ and the deep acceptors Cu+, Ag+, and Te2– produced primarily slow donor–acceptor emissions at peak wavelengths of 605, 653, and 800nm, respectively. The luminosity of the samples doped with La3+ and Cu+ depended strongly on the La3+ concentration, demonstrating its role as an electron donor. First-principles band structure calculations showed (1) that the donor level depth of an isolated iodine vacancy is about 0.8eV, too deep to explain the 520nm emission wavelength, and (2) that a donor–acceptor pair consisting of a spatially associated iodine vacancy donor and a lead vacancy acceptor has shallower donor and acceptor depths that are consistent with the 520nm emission wavelength. [Copyright &y& Elsevier]