| 1. |
- Aidas, Kestutis, et al.
(författare)
-
The Dalton quantum chemistry program system
- 2014
-
Ingår i: WIREs Computational Molecular Science. - : Wiley. - 1759-0876 .- 1759-0884. ; 4:3, s. 269-284
-
Tidskriftsartikel (refereegranskat)abstract
- Dalton is a powerful general-purpose program system for the study of molecular electronic structure at the Hartree-Fock, Kohn-Sham, multiconfigurational self-consistent-field, MOller-Plesset, configuration-interaction, and coupled-cluster levels of theory. Apart from the total energy, a wide variety of molecular properties may be calculated using these electronic-structure models. Molecular gradients and Hessians are available for geometry optimizations, molecular dynamics, and vibrational studies, whereas magnetic resonance and optical activity can be studied in a gauge-origin-invariant manner. Frequency-dependent molecular properties can be calculated using linear, quadratic, and cubic response theory. A large number of singlet and triplet perturbation operators are available for the study of one-, two-, and three-photon processes. Environmental effects may be included using various dielectric-medium and quantum-mechanics/molecular-mechanics models. Large molecules may be studied using linear-scaling and massively parallel algorithms. Dalton is distributed at no cost from for a number of UNIX platforms.
|
|
| 2. |
- GUO, JH, et al.
(författare)
-
RESONANT AND NONRESONANT X-RAY-SCATTERING FROM C-70
- 1995
-
Ingår i: CHEMICAL PHYSICS LETTERS. - : ELSEVIER SCIENCE BV. - 0009-2614. ; 235:1-2, s. 152-159
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Resonant and non-resonant X-ray scattering spectra of the C-70 molecule are presented and analyzed by ab initio Hartree-Fock calculations using a newly developed formalism for symmetry selective inelastic X-ray scattering. Compared to C-60, a weak excitat
|
|
| 3. |
- Jonsson, D., et al.
(författare)
-
Magnetic hyperpolarizabilities in a cubic response formulation
- 1996
-
Ingår i: Theoretical Chemistry accounts. - 1432-881X .- 1432-2234. ; 93:4, s. 235-241
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the applicability of a recently derived cubic response function formalism for performing fully analytical calculations of hypermagnetizabilities, their anisotropy and their dispersion. The calculations involve the noble gas atoms, He, Ne, and Ar, and the corresponding isoelectronic halogen anions and alkali cations.
|
|
| 4. |
- Jonsson, D., et al.
(författare)
-
The hypermagnetizability of molecular oxygen
- 1997
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 106:20, s. 8552-8563
-
Tidskriftsartikel (refereegranskat)abstract
- The hypermagnetizability and the hypermagnetizability anisotropy of the oxygen molecule are computed using cubic response theory applied to multi-configurational self-consistent field wave functions. The effects of basis set, electron correlation, frequency dispersion, zero point vibrational averaging and pure vibrational contributions are discussed. The result for the anisotropy (Δη = + 2.65 a.u. at λ = 632.8 nm), even taking into account possible limitations in the treatment of electron correlation and in the incompleteness of the basis set, maintains a different sign and is more than two orders of magnitude smaller than the experimental values published in the literature. Possible reasons for this large discrepancy are discussed. © 1997 American Institute of Physics.
|
|
| 5. |
- Kaznacheyev, K., et al.
(författare)
-
Innershell absorption Spectroscopy of amino acids
- 2002
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 106:13, s. 3153-3168
-
Tidskriftsartikel (refereegranskat)abstract
- We present comprehensive measurements of the C (carbon) K edge near-edge X-ray absorption (NEXAFS) spectra of all 20 amino acids commonly occurring in nature. Qualitative trends among the spectra of amino acids with similar chemical character are identified and spectral features are compared with extensive ab initio calculations. The contributions of individual units and substitutional groups have been determined to explore their fingerprinting character using the building block concept. Several such units are found. Two that give particularly clear features in the C Is NEXAFS spectra are the carboxyl group (which can be clearly identified by a pronounced structure due to the C 1s-->pi*c-o transition with maximum at 288.65(5) eV) and modified phenol rings in aromatic amino acids (which give sharp C 1s-->pi*c=o structures). The latter transitions are located around 285 cV, and their shape is specific for each aromatic amino acid. Other building blocks, such as the CNHn group and the CH, CC, CO, CN pair bonds, are also identified, although their characteristic features are less pronounced in the C K edge spectra than the carboxylic and aromatic structures. This study provides the basis for rigorous assignment of the NEXAFS spectra of the amino acids, and will be helpful in developing X-ray absorption spectroscopy for quantitative analysis of proteins.
|
|
| 6. |
- KNUTS, S, et al.
(författare)
-
SPIN-ORBIT-COUPLING IN THE INTERSYSTEM CROSSING OF THE RING-OPENED OXIRANE BIRADICAL
- 1995
-
Ingår i: INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY. - 0020-7608. ; 55:1, s. 23-34
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The intersystem crossing (Isc) between the lowest triplet and singlet states occurring in the reaction of atomic oxygen with ethylene was studied. The importance of spin-orbit coupling (sec) in oxirane biradicals (CR'R ''-CRR*-O) is stressed through calcu
|
|
| 7. |
- Loboda, O., et al.
(författare)
-
Ab initio calculations of zero-field splitting parameters in linear polyacenes
- 2003
-
Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 286:1, s. 127-137
-
Tidskriftsartikel (refereegranskat)abstract
- The results of ab initio calculations of zero-field splitting (ZFS) parameters are presented for the linear polyacenes from benzene to pentacene. We show how the electron spin-spin (SS) parameters can be efficiently obtained from restricted high-spin open-shell wave functions (ROHF), and present calculations of these, comparing with the results of a recent multi-configurational self-consistent field approach. The SS parameters are obtained from electron SS coupling strengths evaluated as expectation values over the wave functions and from state-to-state spin-orbit (SO) interactions. The results for the two lowest triplet states of naphthalene demonstrate that excellent values can be obtained even using moderate basis sets in the wave function, indicating that this technique can be used to obtain reliable ZFS parameters of aromatic compounds. Electron correlation is, however, not negligible; by accounting for full pi-electron correlation the ZFS parameters are in considerably better agreement with experiment than the ROHF results. The ROHF method still reproduced the qualitative trend in the polyacene series in which the ZFS parameters are reduced with increasing size of the pi-conjugation. We confirm that the SS coupling contributions completely determine the D and E parameters for the lowest triplet state of the linear polyacenes and that the SO coupling contributions are small. Geometry optimization of the lowest triplet state was found to be fairly significant for the calculated D and E values; these were reduced by about 30% and 40%, respectively, when the geometry was changed from the ground-state singlet to the triplet-excited state optimized geometry, with the latter values being in better agreement with experiment. The present calculations predict that the second triplet state of naphthalene is very unusual, as it has a negative zero-field splitting, implying an altered ordering of the spin sublevels compared to what is common in aromatic systems.
|
|
| 8. |
- Loboda, O., et al.
(författare)
-
Ab initio study of nonhomogeneous broadening of the zero-field splitting of triplet guest molecules in diluted glasses
- 2003
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:6, s. 3120-3129
-
Tidskriftsartikel (refereegranskat)abstract
- Nonhomogeneous broadening of phosphorescence lines and microwave signals in optical detection of magnetic resonance (ODMR) has been calculated using multiconfigurational self-consistent field wave functions and the polarized continuum model. The solvent effects on the zero-field splitting (ZFS) parameters in the low-lying triplet states of aza-aromatic molecules are found to be linearly dependent on the solvent-induced shifts in the phosphorescence frequency in agreement with experimental data. The main contribution to the ZFS originates in the dipolar interaction of the two electron spins, the spin-spin coupling. The spin-orbit coupling (SOC) contribution to the ZFS parameter is much larger for the (3)npi(*) state of pyrazine compared to the (3)pipi(*) states of quinoline. The second-order SOC contribution to the splitting of the (3)npi(*) state in the pyrazine molecule does not show any appreciable dependence on the dielectric constant of the solvent. This raises doubts about earlier theories for explaining the inhomogeneous broadening in triplet-state spectra based exclusively on the SOC-induced mixing of the singlet and triplet states. We complete the interpretation of the ODMR spectrum of pyrazine by calculating the hyperfine coupling (HFC) tensors in the lowest triplet state using the UB3LYP hybrid functional. An appreciable solvent-induced rotation of the anisotropic HFC tensor axes has been obtained for the (3)npi(*) state of pyrazine, in particular for C-13 and N-14 nuclei. This produces additional nonhomogeneous broadening not only in electron-nuclear double resonance spectra, but also in electron paramagnetic resonance signals because the anisotropic HFC perturbation results in an intensity redistribution among the magnetic transitions between the spin sublevels. A small in-plane rotation of the ZFS tensor axes upon solvation has been predicted for quinoline. Rotation of the magnetic axes induced by the interaction with isotropic solvents can provide a new mechanism for spin-lattice relaxation in the triplet state.
|
|
| 9. |
- Luo, Y., et al.
(författare)
-
Some recent developments of high-order response theory
- 1998
-
Ingår i: International Journal of Quantum Chemistry. - 0020-7608 .- 1097-461X. ; 70:1, s. 219-239
-
Tidskriftsartikel (refereegranskat)abstract
- We review some recent developments of high-order response theory and illustrate the utility of this theory for a selection of nonlinear properties. © 1998 John Willey & Sons, Inc.
|
|
| 10. |
- Minaev, B., et al.
(författare)
-
Fine and hyperfine structure in three low-lying (3)Sigma(+) states of molecular hydrogen
- 2003
-
Ingår i: Molecular Physics. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 101:15, s. 2335-2346
-
Tidskriftsartikel (refereegranskat)abstract
- The fine structure constant (electron spin-spin coupling) and the hyperfine structure parameters (electron-nuclear spin coupling, including spin-rotation and electron-nuclear quadrupole coupling) in the low-lying triplet states b (3)Sigma(u)(+), a (3)Sigma(g)(+) and e (3)Sigma(u)(+) of molecular hydrogen and deuterium are calculated using a recently developed technique with full configu-ration interaction and multiconfiguration self-consistent field wave functions. The second-order spin-orbit coupling contribution to the (3)Sigma(+) states splitting is negligible, and the calculations therefore provide a good estimate of the zero-field splitting based only on the electron spin-spin coupling values. For the bound state a (3)Sigma(g)(+) negligible zero-field splitting is found, in qualitative agreement with the e-a spectrum. The zero-field splitting parameter is considerable for the repulsive b (3)Sigma(u)(+) state (similar or equal to1 cm(-1) ) and of intermediate size for the bound e (3)Sigma(u)(+) state. The isotropic hyperfine coupling constant is very large not only for the valence b (3)Sigma(u)(+) state (1580 MHz) but also for the Rydberg a and e triplet states (similar or equal to1400 MHz). The quadrupole coupling constants for the deuterium isotopes are negligible (0.04-0.07 MHz) for all studied triplet states. The electric dipole activity of the spin sublevels in the triplet-singlet transitions to the ground state is estimated by means of the quadratic response technique.
|
|
