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| 2. |
- Piancastelli, MN, et al.
(författare)
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Bond-distance-dependent decay probability of the N 1s -> pi* core-excited state in N-2
- 2000
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Ingår i: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. - : IOP PUBLISHING LTD. - 0953-4075. ; 33:9, s. 1819-1826
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Tidskriftsartikel (refereegranskat)abstract
- We report the observation of the unusually weak decay of the N 1s --> pi* core-excited N-2 molecule to the (B) over tilde (2)Sigma(u)(+) final state of N-2(+), which is only detectable in an experiment with high sensitivity. The resonant Auger spectra exh
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| 3. |
- Salek, P, et al.
(författare)
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Dynamical suppression of atomic peaks in resonant dissociative photoemission
- 2001
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Ingår i: CHEMICAL PHYSICS LETTERS. - : ELSEVIER SCIENCE BV. - 0009-2614. ; 343:3-4, s. 332-338 Language: English
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Tidskriftsartikel (refereegranskat)abstract
- Resonant excitation to the F1s-sigma* dissociative state in hydrogen fluoride gives a photoelectron spectrum where the spectator part contains strong atomic lines but a participator part where such lines are lacking. We demonstrate that this contrasting b
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| 4. |
- Sałek, P., et al.
(författare)
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Resonant X-ray Raman scattering involving avoided crossings in the final-state potential-energy curves
- 2000
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Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 1050-2947. ; 62:6, s. 62501-62506
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Tidskriftsartikel (refereegranskat)abstract
- The effect of avoided crossings on the spectral profiles of resonant X-ray Raman scattering was investigated. The theory was also applied to nitrogen molecule in the core-excited level to analyze the electron decay process. The dependence of internuclear distance on electron transition amplitude was considered important with respect to the breakdown process of the transition. The correlation between the nuclear and electronic degrees of freedom was also reported.
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| 5. |
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| 6. |
- Thogersen, L., et al.
(författare)
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The trust-region self-consistent field method : Towards a black-box optimization in Hartree-Fock and Kohn-Sham theories
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:1, s. 16-27
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Tidskriftsartikel (refereegranskat)abstract
- The trust-region self-consistent field (TRSCF) method is presented for optimizing the total energy E-SCF of Hartree-Fock theory and Kohn-Sham density-functional theory. In the TRSCF method, both the Fock/Kohn-Sham matrix diagonalization step to obtain a new density matrix and the step to determine the optimal density matrix in the subspace of the density matrices of the preceding diagonalization steps have been improved. The improvements follow from the recognition that local models to E-SCF may be introduced by carrying out a Taylor expansion of the energy about the current density matrix. At the point of expansion, the local models have the same gradient as E-SCF but only an approximate Hessian. The local models are therefore valid only in a restricted region-the trust region-and steps can only be taken with confidence within this region. By restricting the steps of the TRSCF model to be inside the trust region, a monotonic and significant reduction of the total energy is ensured in each iteration of the TRSCF method. Examples are given where the TRSCF method converges monotonically and smoothly, but where the standard DIIS method diverges.
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| 7. |
- Watson, M. A., et al.
(författare)
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Linear-scaling formation of Kohn-Sham Hamiltonian : Application to the calculation of excitation energies and polarizabilities of large molecular systems
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:7, s. 2915-2931
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Tidskriftsartikel (refereegranskat)abstract
- We present calculations of excitation energies and polarizabilities in large molecular systems at the local-density and generalized-gradient approximation levels of density-functional theory (DFT). Our results are obtained using a linear-scaling DFT implementation in the program system DALTON for the formation of the Kohn-Sham Hamiltonian. For the Coulomb contribution, we introduce a modification of the fast multipole method to calculations over Gaussian charge distributions. It affords a simpler implementation than the original continuous fast multipole method by partitioning the electrostatic Coulomb interactions into classical and nonclassical terms which are explicitly evaluated by linear-scaling multipole techniques and a modified two-electron integral code, respectively. As an illustration of the code, we have studied the singlet and triplet excitation energies as well as the static and dynamic polarizabilities of polyethylenes, polyenes, polyynes, and graphite sheets with an emphasis on the trends observed with system size.
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| 8. |
- Watson, M. A., et al.
(författare)
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The calculation of indirect nuclear spin-spin coupling constants in large molecules
- 2004
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 10:18, s. 4627-4639
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Tidskriftsartikel (refereegranskat)abstract
- We present calculations of indirect nuclear spin-spin coupling constants in large molecular systems, performed using density functional theory. Such calculations, which have become possible because of the use of linear-scaling techniques in the evaluation of the Coulomb and exchange-correlation contributions to the electronic energy, allow us to study indirect spin-spin couplings in molecules of biological interest, without having to construct artificial model systems. In addition to presenting a statistical analysis of the large number of short-range coupling constants in large molecular systems, we analyse the asymptotic dependence of the indirect nuclear spin-spin coupling constants on the internuclear separation. In particular, we demonstrate that, in a sufficiently large one-electron basis set, the indirect spin-spin coupling constants become proportional to the inverse cube of the internuclear separation, even though the diamagnetic and paramagnetic spin-orbit contributions to the spin-spin coupling constants separately decay as the inverse square of this separation. By contrast, the triplet Fermi contact and spin-dipole contributions to the indirect spin-spin coupling constants decay exponentially and as the inverse cube of the internuclear separation, respectively. Thus, whereas short-range indirect spin-spin coupling constants are usually dominated by the Fermi contact contribution, long-range coupling constants are always dominated by the negative diamagnetic spin-orbit contribution and by the positive paramagnetic spin-orbit contribution, with small spin-dipole and negligible Fermi contact contributions.
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