| 1. |
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| 2. |
- Edvardsson, Sverker, et al.
(författare)
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A program for accurate solutions of two-electron atoms
- 2004
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 165:3, s. 260-270
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Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensible computer program capable of treating non-relativistic ground and excited states for a twoelectron atom having infinite nuclear mass. An iterative approach based on the implicitly restarted Arnoldi method (IRAM) is employed. The Hamiltonian matrix is never explicitly computed. Instead the action of the Hamiltonian operator on discrete pair functions is implemented. The finite difference method is applied and subsequent extrapolations gives the continuous grid result. The program is written in C and is highly optimized. All computations are made in double precision. Despite this relatively low degree of floating point precision (48 digits are not uncommon), the accuracy in the results can reach about 10 significant figures. Both serial and parallel versions are provided. The parallel program is particularly suitable for shared memory machines such as the Sun Starcat series. The serial version is simple to compile and should run on any platform.
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| 3. |
- Edvardsson, Sverker, et al.
(författare)
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A search for H/ACA snoRNAs in yeast using MFE secondary structure prediction
- 2003
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Ingår i: Bioinformatics. - : Oxford University Press (OUP). - 1367-4803 .- 1367-4811. ; 19:7, s. 865-873
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Tidskriftsartikel (refereegranskat)abstract
- We develop an algorithm to screen the yeast genome for novel H/ACA snoRNAs. To achieve this, we introduce some new methods for facilitating the search for noncoding RNAs in genomic sequences which are based on properties of predicted minimum free-energy (MFE) secondary structures. The algorithm has been implemented and can be generalized to enable screening of other eukaryote genomes. We find that use of primary sequence alone is insufficient for identifying novel H/ACA snoRNAs. Only the use of secondary structure filters reduces the number of candidates to a manageable size. From genomic context, we identify three strong H/ACA snoRNA candidates. These together with a further 47 candidates obtained by our analysis are being experimentally screened.
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| 4. |
- Edvardsson, Sverker, et al.
(författare)
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Accurate spin axes and solar system dynamics: climatic variations for the Earth and Mars
- 2002
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 384:2, s. 689-701
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Tidskriftsartikel (refereegranskat)abstract
- Celestial mechanical simulations from a purely classical point of view of the solar system, including our Moon and the Mars moons {Phobos and Deimos {are carried out for 2 millions of years before present. Within the classical approximation, the results are derived at a very high level of accuracy. Effects from general relativity for a number of variables are investigated and found to be small. For climatic studies of about 1 Myr, general relativity can safely be ignored. Three different and independent integration schemes are used in order to exclude numerical anomalies. The converged results from all methods are found to be in complete agreement. For verification, a number of properties such as spin axis precession, nutation, and orbit inclination for Earth and Mars have been calculated. Times and positions of equinoxes and solstices are continously monitored. As also observed earlier, the obliquity of the Earth is stabilized by the Moon. On the other hand, the obliquity of Mars shows dramatic variations. Climatic influences due to celestial variables for the Earth and Mars are studied. Instead of using mean insolation as in the usual applications of Milankovitch theory, the present approach focuses on the instantaneous solar radiation power (insolation) at each summer solstice. Solar radiation power is compared to the derivative of the icevolume and these quantities are found to be in excellent agreement. Orbital precessions for the inner planets are studied as well. In the case of Mercury, it is investigated in detail.
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| 5. |
- Edvardsson, Sverker, et al.
(författare)
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An atomic program for energy levels of equivalent electrons: lanthanides and actinides
- 2001
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Ingår i: Computer Physics Communications. - 0010-4655 .- 1879-2944. ; 133:2/3, s. 396-406
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Tidskriftsartikel (refereegranskat)abstract
- A program written in C is presented to carry out brute force calculations in order to derive energy levels for an equivalent electronic configuration. Relativistic effects are partly neglected except for the spin-orbit interaction. Since the main relativistic effects are indirect, i.e. causing a contraction of the core which in turn causes the outer shells to expand, they are included to a high degree through the use of appropriate Slater integrals. The program is especially useful for primarily unfilled f-shells of the rare-earth or actinide ions. Modifications of the program to include spin−spin, spin−other orbit, Breit interaction etc. is straight forward. The program is also general in the sense that there is no need to find out or generate any Racah coefficients of fractional parentage. The complete energy matrix is diagonalized with all operators interacting simultaneously thus allowing mixing of all quantum numbers. This result in all energy eigenvalues and eigenvectors that in turn for example are partly responsible for the polarized dipole, quadrupole, … transitions within the unfilled shell. Free ion configuration interaction is accounted for through the use of standard CI operators. The Stark splitting can be studied via the standard crystal field Hamiltonian. Magnetic field influence on the energy levels may also be studied.
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| 6. |
- Edvardsson, Sverker
(författare)
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Future iceages for the next 100,000 years
- 2002
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Ingår i: The handling of timescales in assessing post-closure safety of deep geological repositories. - Paris : Nuclear Energy Agency, OECD. - 9264099115 ; , s. 212-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Edvardsson, Sverker, et al.
(författare)
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The energy matrix using determinantal product states applied to Ho:YAG
- 2000
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Ingår i: Journal of Alloys and Compounds. - 0925-8388 .- 1873-4669. ; 303-304, s. 280-284
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Tidskriftsartikel (refereegranskat)abstract
- A program written in C is applied for calculations of energy levels and wavefunctions of the lanthanides or actinides. Standard non-relativistic phenomenological operators are used. Simple determinantal product states are used to form the basis set. The complete energy matrix is diagonalized with all operators interacting simultaneously thus allowing mixing of all quantum numbers. The crystal field splitting can also be studied via the standard crystal field hamiltonian as well as the magnetic field influence on the energy levels. The program is here applied to the technologically interesting trivalent ion holmium which is used to form extremely strong magnets as well as the medical eye-safe laser Ho:YAG. Both experimentally fitted and calculated self-consistent crystal field parameters are used to study the energy structure. Crystal ionic polarizabilities with electron correlation included are partly calculated. Zeeman split levels are also studied.
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| 8. |
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| 9. |
- Wessely, Ola, et al.
(författare)
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Initial and final state effects in the x-ray absorption process of La1-xSrxMnO3
- 2003
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Ingår i: Physical Review B : Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:23, s. 235109-1
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Tidskriftsartikel (refereegranskat)abstract
- We have probed the electronic structure of La1-xSrxMnO3 using x-ray absorption spectroscopy, and compared our results to theory. It is shown that the O projected spectrum reveals a signal that is consistent only with hybridized and delocalized Mn d-states whereas the Mn projected spectrum reveals a signal that can only be reproduced by atomic like theory allowing for multiplet formation between the core hole and the valence electrons of the final state. Our results indicate that the ground state electronic structure has delocalized Mn d-states. This is discussed to be caused by a dynamical screening of the core hole created in the absorption process.
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| 10. |
- Wessley, O, et al.
(författare)
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Final state effects in the X-ray absorption spectra of La0.7Sr0.3MnO3
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 272-276:3, s. 1780-1781
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Tidskriftsartikel (refereegranskat)abstract
- We present a comparison of theoretical calculations of the electronic structure of La0.7Sr0.3MnO3 with measurements of the unoccupied local density of states for Mn obtained from X-ray absorption spectroscopy (XAS). We compare two different theoretical calculations of the Mn XAS spectra, one based on the local spin density approximation (LSDA) and the other one based on an atomic Hartree–Fock calculation for the Mn ions. In the atomic calculation the solid state effects are introduced through a cubic crystal field where the crystal field strength is obtained from the LSDA calculation. It is found that the atomic calculations agree better with experimental data.
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| 11. |
- Åberg, Daniel, et al.
(författare)
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Direct calculation of correlated absorption amplitudes for Nd:LiYF4
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:19
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Tidskriftsartikel (refereegranskat)abstract
- The correlation contribution to the transition amplitudes are investigated in the case of Nd:LiYF4. By using many-body perturbation theory, we derive expressions for an effective dipole operator. The operators considered are Omega(es)((1)dagger)DOmega(cf)((1)), Omega(cf)((1)dagger)DOmega(es)((1)), Omega(es-cf)((2)dagger)D, and DOmega(es-cf)((2)). In contrast to third-order spin-orbit and crystal-field modified amplitudes, inclusion of correlation modifies the standard second-order amplitudes significantly. A model cluster is optimized to experimental energy levels. This approach is then used to compute consistent odd and even crystal-field parameters needed for theoretical absorption spectra. As expected, it is observed that transitions occurring at small wavelengths are quite heavily influenced by correlation. The overall agreement between experimental and theoretical spectra below 600 nm (above 17000 cm(-1)) is greatly improved when correlation is taken into account.
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| 12. |
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| 13. |
- Åberg, Daniel, et al.
(författare)
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The crystal dependent open-shell polarizability of f-elements : higher order contributions
- 2000
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Ingår i: Journal of Alloys and Compounds. - 0925-8388 .- 1873-4669. ; 303-304:24 May, s. 345-348
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Tidskriftsartikel (refereegranskat)abstract
- It has earlier been shown that the use of a self consistent multipole electrostatic model to derive the crystal field parameters (CFP) actually gives the correct curve shape when the CFP are plotted against the various rare-earth ions (S. Edvardsson, M. Klintenberg, The use of CI calculated polarizabilities to study rare-earth CFP dependencies in the laser host RE:YLF. Mater. Sci. Forum, 1999;315-317:407). It is also known that the electrostatic contribution is important for the lower order parameters. In this connection; our primary interest is to revisit this model and investigate theoretically some aspects of the dipole polarizability (alpha(D)). A few approximations were done in the earlier calculations: the treatment of unfilled shells, the neglect that also higher order terms of the type A(10)r(t)C(0)(t) contribute with t odd (not only the A(10)r(1)C(0)(1) term), correlation effects and second order contributions in perturbation theory. The solutions of the inhomogeneous Schrodinger equation are solved by a powerful numerical method. The problem is reformulated and results instead in a simple linear equation system (symmetric tridiagonal matrix) which is stable and fast to solve. The various theoretical results will be used in future applications.
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| 14. |
- Åberg, Daniel, 1974-
(författare)
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Transition Properties of f-electrons in Rare-earth Optical Materials
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main purpose of this thesis is to theoretically study energy levels and intra-electronic transition intensities for various f-electron systems. The f-f electronic dipole transitions are parity-forbidden for a free ion but become non-zero when the ion is subject to a crystal-field. This is commonly described within the framework of Judd-Ofelt theory which accounts for the mixing of odd parity into the wave-functions. Some refinements and quantitative studies have been made by applying many-body perturbation theory, or the perturbed functions approach, to obtain effective dipole operators due to correlation, spin-orbit and higher order crystal-field effects not included in Judd-Ofelt theory. A software for the computation of f-electron multiplets and Stark levels was implemented and published as well. The single- and pair-functions used for the evaluation of intensity parameters were obtained by solving various inhomogeneous Schrödinger equations. The wave-functions and energies obtained by diagonalizing an effective Hamiltonian have been used together with the oscillator strength methods to simulate absorption spectrum. Consistent crystal-field parameters applied in some of the papers were obtained by fitting crystal polarizabilities to reflect the experimental Stark levels. The same crystal model was then used to generate odd crystal field parameters needed for the f-f transition intensities. The total effect of these refinements are spectral features that usually agree well with experimental findings. Some of these methods have also been applied and seen to be quite useful for the understanding of optical fiber amplifiers frequently used in today's optical networks. Finally, a finite-difference approach was applied for the Helium iso-electronic sequence. The exact wave-function was expanded in a sum of partial waves, and accurate ground- and excited state energies were obtained by using the iterative Arnoldi approach.
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